Sleep diagnostic equipment - Philips Respironics

Sleep diagnostic
equipment

An introduction for the sleep technologist

Table of contents

Introduction 3

Evaluating airflow using a nasal pressure transducer 4

Nasal airflow pressure transducer 4

Airflow sensing devices 5

Identification of apneas, hypopneas and RERA events 6

Obstructive apnea/hypopneas event 6

Respiratory effort-related arousals 6

PTAF2 7

Interfacing the PTAF2 with a polysomnograph 8

Interfacing the PTAF2 with a positive pressure device 10

Understanding the PTAF2 flow tracing 10

Frequently asked questions (FAQ) and bibliography 13

Pulse transit time as a measurement parameter 14

Pulse transit time (PTT) as a measurement parameter 14

Method of measurement 15

Micro-arousal recognition using pulse transit time 16

Recognition of events using pulse transit time 16

Limitation of using PTT 18

PTT and CPAP 18

Bibliography 19

An introduction to RIP 20

Applications of respiratory inductance plethysmography 22

Recording RIP effort signals 22

Waveform samples 23

Setting up the patient and fitting the belt 24

Adjustments 24

Bibliography 27

Evaluation form and post-test tear out section

2

An introduction to sleep diagnostic equipment

This self-directed monograph consists of three individual chapters that review the difference between
various nasal pressure airflow systems, pulse transit time (PTT) and respiratory inductance plethysmography
(RIP), as they relate to the diagnosis of sleep-disordered breathing.

This three-credit program includes information regarding: nasal pressure
transducers; airflow tracings and how they are recorded and evaluated
during a sleep study to determine an apnea or hypopnea; pulse transit
time in relation to arousals and microarousals; how data are interpreted
as related to sleep related arousals and RERAs; the importance and
applications of respiratory effort as a measured parameter; and, how
to set up, use, clean and score a RIP system.
We would like to extend a thank you to the following individuals:
Dr. Gandis G. Mazeika and Rick Swanson RPSGT, CRT, for allowing us
to use their paper on Respiratory Inductance Plethysmography as a
basis for the Respiratory Inductance Plethysmography monograph.
We also would like to thank them for allowing us to use tracings and
graphics from their paper.
A thank you to Dr. R.Tamisier, Dr. J. L. Pepin, and Dr. P. Levy for providing
the content and graphics from their paper on Pulse Transit Time as a
basis for the Pulse Transit Time monograph.

Obstructive Sleep Apnea (OSA)

To date, information on clinical research with respect to the relationship between
OSA and various co-morbidities is still being established.While the relationship
has been established between OSA and various disease states discussed in this
publication, research is ongoing to identify potential causative relationships
between OSA and other disease states.

3

Evaluating airflow using a
nasal pressure transducer

Polysomnography is the collection of multiple parameters of biological data used to determine the
presence of sleep disorders.The information is a direct reflection of physiological activities occurring
in various parts of the body such as brain, heart and lungs.The primary channels used to evaluate a
patient’s breathing function are airflow and respiratory effort.

Main focus of this booklet Nasal airflow pressure transducer

The main focus of this booklet is to explore the impor- The importance of the accurate identification of changes in respiratory
tance of a reliable airflow signal in the diagnosis of SDB. parameters has increased with the growing awareness of the link
This paper will explore: between Sleep Disordered Breathing (SDB) and co-morbidities such
• The sensors used to detect airflow as hypertension.The Wisconsin Sleep Cohort Study is an ongoing
• The use of a pressure transducer to record subtle study that evaluates participants every four years. In this study, it was
found that participants with an initial apnea/hypopnea index (AHI) of
changes in the airflow signal 0.1 to 4.9, have a 42% greater chance of developing hypertension than
• Understanding the PTAF2 system the control group with an AHI of zero.As the AHI increases, the odds
• Evaluating tracings that are generated with a pressure of developing hypertension also increase.1 According to Exar and
Collop, hypertension is a sequela of upper airway resistance that more
transducer than likely results from autonomic and cardiovascular changes.2 Data
• Troubleshooting signals also shows the development of OSA in postmenopausal women.
According to Bixler,“menopause is a significant risk factor for sleep
apnea, and HRT may be associated with reduced risk.”3

The airflow signal is one of the parameters used to determine if a
patient has Sleep Disordered Breathing.The airflow signal may show:

Periodic lapse of airflow – apnea

Periodic decrease in the amplitude of airflow – hypopnea

Change in the morphology or squaring off of the airflow signal signifying a partial
closure or relaxation of the airway also known as flow limitation.
4

Airflow sensing devices Alternative methods
Other ways to measure airflow or lung volumes are more accurate
Thermistor and thermocouple but have significant limitations in the clinical setting. Inductance
The thermistor and thermocouple are both thermal-based flow devices. plethysmography measures lung volumes by the compartmental changes
These devices use a change in air temperature to record changes in in the chest wall during breathing, but must be calibrated prior to the
breathing. In both devices, a sensor is placed above the upper lip and sleep study. If the patient moves during sleep – as most patients do –
usually uses three wires to sense temperature changes. the calibration becomes unreliable. If the position of the belt moves,
the signal may become unusable.The most accurate way of measuring
The wires are positioned to sense the change in temperature that airflow is with a pneumotachograph.This device is placed in a full face
occurs within a normal breathing cycle.A wire is positioned in front mask and all the air the patient breathes must go through the device
of each nare and the third wire is positioned in front of the mouth. to accurately measure the amount of airflow.This can be uncomfortable
Exhaled air, warmed by the body, heats the sensor. Inhaled air, pulled for the patient and is unrealistic to use in a clinical setting.
from the environment, cools the sensor.These temperature changes
are then converted to a signal that denotes airflow fluctuations and Pressure sensing device
is recorded as airflow on the polysomnogram. A device that is becoming the standard for monitoring airflow is the
pressure sensing device.This device uses a nasal cannula connected to
Some potential problems may arise when using the thermal-based flow a very sensitive pressure transducer and produces a signal that is quite
detectors. For example, the Pro-Tech primer on nasal pressure airflow comparable to the pneumotachograph.
measurement reports that thermistors under-detect respiratory
events by estimates of up to 70% for apneas and hypopneas that are
not well defined.4,6,7

In an unfriendly environment or when the temperature differentiation
is minimal, the thermal-based sensors may produce signals that are dif-
ficult to read.A warm room, or a room that has an oscillating fan or a
fan directed toward the patient, may result in an inaccurate or difficult-
to-read tracing. If a thermal-based sensor is used with a positive-pressure
device, the air flowing through the mask (especially at high pressures
or in the presence of a mask leak) may become so diluted that it
becomes useless or difficult to read.

A nasal cannula tracing utilizing a pressure transducer demonstrates flow limitation
by a squaring off of the waveform.This is consistent with a partial closure of the
airway and is a much easier way to identify hypopneas.

The thermal airflow signal becomes unreliable when used with a
positive pressure device such as CPAP.

5

Identification of apneas, hypopneas and RERA events By following the preceeding guidelines for scoring respiratory events,
apneas and hypopneas can be easily identified.The scoring of RERAs,
According to the Clinical Practice Review Committee,American Academy on the other hand, relies on the use of an esophageal pressure
of Sleep Medicine in Hypopnea in Sleep-Disordered Breathing in Adults, catheter or balloon.This method can be very uncomfortable for the
apneas, hypopneas and Respiratory Effort Related Arousals (RERA)5 are patient.Therefore, very few sleep labs use esophageal pressure to
defined as follows: measure RERAs. Instead, the majority of labs rely on the inference
that if arousals, snoring and subtle respiratory effort changes are
Obstructive apnea/hypopnea event resolved or reduced by nasal CPAP, then RERAs were present and
An event characterized by a transient reduction in, or complete cessation have been treated.
of, breathing. In routine clinical practice it is not considered necessary
to distinguish obstructive hypopneas from apneas because both types of Dr. Rapoport, et al. state in Nasal Pressure Airflow Measurement:An
events have similar pathophysiology.These events must fulfill criterion Introduction, Pro-Tech Primer4:
one or two plus criterion three of the following:
“Recent data shows that the nasal cannula technique contains information
1. A clear decrease (>30%) from baseline in the amplitude of a valid about respiratory airflow not found in the thermistor, and can be used
measure of breathing during sleep. Baseline is defined as the mean to detect the subtle flow/resistance changes characteristic of UARS
amplitude of stable breathing and oxygenation in the two minutes (now called RERA) with results similar to those obtained with an
preceding onset of the event (in individuals who have a stable esophageal manometer.”
breathing pattern during sleep) or the mean amplitude of the three
largest breaths in the two minutes preceding onset of the event (in The American Academy of Sleep Medicine (AASM) guidelines state
individuals without a stable breathing pattern). that with respect to scoring a RERA, use of esophageal pressure is the
preferred method of assessing change in respiratory effort, although
2. A clear amplitude reduction of a validated measure of breathing nasal pressure and inductance plethysmography can be used.8
during sleep that does not reach the above criterion but is associ-
ated with either an oxygen desaturation of >4% or an arousal.

3. The event lasts ten seconds or longer.

Respiratory effort-related arousals
An RERA is a sequence of breaths characterized by increasing respiratory
effort leading to an arousal from sleep, but which does not meet the
criteria for an apnea or hypopnea.These events must fulfill both of
the following criteria:

1. Pattern of progressively more negative esophageal pressure, esophageal pressure cannula event
terminated by a sudden change in pressure to a less negative level
and an arousal.

2. The event lasts ten seconds or longer.

This tracing is a comparison of an esophogeal pressure catheter
and a cannula with a pressure transducer.

6

PTAF2 qualitative device that requires no periodic calibration.The self-test
may be recorded to document functionality of the equipment.
The PTAF2 is a pressure transducer that utilizes an airflow sensor
cannula to monitor respiratory pressure changes and snoring during During the patient calibrations, the pressure flow signal should corre-
sleep.The transducer takes the pressure input and converts it to an spond to the instructions given to the patient by the sleep technologist.
electrical signal that can be read and recorded by the polysomnograph. When the patient is instructed to inhale, the recording should show a
negative or upward defection. If the recording does not show a negative
The PTAF2 sensor is positioned on the upper lip in the same way as or upward defection, the polarity on that channel should be changed.
an oxygen cannula.The nasal/oral prongs are positioned in areas to When the patient is asked to snore, if using the non-filtered selection
sense changes in pressure as the person inhales and exhales. on the PTAF2, the tracing should show a flattening of the waveform and
a series of fast, low-amplitude, high-frequency waveforms. If using the
filtered setting, the tracing should show only a flattening of the waveform.

Positioning of the nasal/oral prongs: Equipment self-test
(1) Properly trimmed, the openings of the nasal cannula
Non-filtered waveform
will be just inside the nares, in the airflow path.
(2) The tip of the oral cannula should be trimmed to

lie just at the place where the upper and lower
lips meet.

If the nasal/oral prongs are too long they may be trimmed to allow for
the best positioning to receive airflow. It is important not to block the
cannula sensor tips during set-up and recording.

The disposable Pro-Flow cannulas are specially designed for PTAF. Filtered waveform
They are labeled for single-patient use only.
Patient calibrations
To facilitate changes in gain (adjusting the amplitude of the signal) and
performance of a self-test, the PTAF2 system has an optional remote When the set-up is complete, the gain set button is used to automati-
control that is positioned in the control room. If the lab chooses not to cally optimize the PTAF2’s output level.When the gain set button is
obtain the remote control, the tests may be performed at the bedside. depressed, the PTAF2 monitors the patient’s breathing for several
The self-test is used to check the PTAF2’s battery level, electronic breaths and then will set the low- and high-level airflow signals. During
circuitry and the connections to the polysomnograph.The results of the study, if needed, the gain can be adjusted to ensure a good/read-
the self-test may be recorded onto the tracing before the beginning able tracing.
of the study to show the functionality of the device.To verify that the
sensor is correctly positioned and the equipment is working properly, The PTAF2 has no operator serviceable parts except a nine-volt
the sensor should be in place during the patient calibrations. battery. Inspection of the battery and cable connectors is critical in
maintaining proper operation.
To be sure the equipment is working properly, an equipment check
should be performed before the start of a sleep study.The PTAF2 is a

7

Interfacing the PTAF2 with polysomnograph When utilizing either the AC or the DC configurations, the remote is
in the control room with a single cable connecting it to the transducer
The PTAF2 pressure transducer is easily interfaced with a polysomno- that is located in the patient’s room.The patient sensors are also attached
graph and is capable of using either an AC or DC amplifier.As long as to the transducer.When using the AC configuration, the output signal
the AC amplifier filter settings are set properly, the AC and DC amplifier is plugged directly into the jackbox (headbox).There is no need for
are equally acceptable for collecting data.There is no low-frequency additional cables running back to the control room.
filter on the DC amplifier.The signal is amplified as long as the signal is
generated.As the signal decreases, the tracing shows a direct reflection
of that decreased source signal.

In order to best show flow limitation, which may last for over two
seconds, the low-frequency filter setting or time constant on the AC
amplifier, must be set to allow the full signal to be recorded.This means
that the best low-frequency filter setting would be 0.01Hz, which is a
time constant of approximately five seconds.This setting will allow the
AC signal to be comparable to a DC recording. If this low-frequency
filter setting is not available on the polysomnograph, the lowest
acceptable setting is 0.05Hz, or a time constant of three seconds.

Flow (AC) short time constant AC configuration DC configuration
Flow (AC) long time constant

Flow (DC) When interfacing the PTAF2 with the Alice 3 polysomnography system,
a DC auxiliary port is used. If using the Alice 5 system, a variation of
Comparison of a signal recorded with AC amplifiers at different the PTAF Lite has been specifically designed for this integration.The
settings and with a DC amplifier. Alice 5 head box has a dedicated input connection for the PTAF Lite,
another pressure-sensing transducer from Respironics.

When using the DC configuration, most polysomnographs must use The PTAF Lite is a small pressure-sensing transducer that interfaces
an additional cable(s) to go from the PTAF2 transducer in the patient’s with AC amplifiers only. It does not have a filter mode on the transducer.
room to the DC inputs for the polysomnograph in the control room. Filtered signals are achieved by adjusting the high frequency filter on
The PTAF2 DC configuration has an auto-zero to ensure a the polysomnograph.
stable baseline.

8

When the unfiltered output signal is selected, snoring is superimposed Snoring output (snoring only)
on the displayed waveform signal.When the filtered output signal is These settings will filter out the airflow component of the pressure
selected, a nasal pressure airflow waveform is displayed without the signal and present a clean snoring waveform.
superimposed snoring.The filtered channel has an internal 2.5Hz high
frequency filter to remove snoring from the waveform.When snoring Input Sensitivity Low filter High Sampling
with flow limitation occurs with the filtered signal, a flattening of the (time filter frequency
waveform is observed. constant)

Low level 30 uV/mm .05Hz 70Hz 140-200Hz
AC jackbox or lower or higher

(.016 seconds
or longer)

High level Varies with N/A 70Hz 140-200Hz
DC input polysomno- or higher or higher
graph

Filtered output (airflow only)
These settings will filter out the snoring component from the pressure
signal and present a cleaner airflow waveform.

The following are starting points for setting up the polysomnograph. Input Sensitivity Low filter High Sampling
They are typical settings that may be changed depending upon the (time filter frequency
type of polysomnograph used. constant)

Unfiltered output (airflow and snoring together) Low level 30 uV/mm .05Hz 5Hz 10Hz
These settings will allow any snoring component of the pressure to be AC jackbox or lower or higher or higher
superimposed onto the polysomnograph airflow waveform. (3 seconds
or longer)

Input Sensitivity Low filter High Sampling
(time filter frequency
constant) High level Varies with N/A 5Hz 10Hz
DC input polysomno- or higher or higher
graph

Low level 30 uV/mm .05Hz 70Hz 140-200Hz
AC jackbox or lower or higher
(3 seconds
or longer)

High level Varies with N/A 70Hz 140-200Hz
DC input polysomno- or higher
graph

9

Interfacing the PTAF2 with a positive pressure device Many of the following sample tracings are taken directly from Nasal Pres-
sure Airflow Measurement:An Introduction, Pro-Tech Primer4. Let us first
When using the PTAF2 to record flow tracings during titration, there look at a normal breathing waveform and a flow limitation waveform.
are four equipment configurations that may be used.These four config-
urations are listed in the Pro-Tech Primer4.We will briefly discuss two Normal breathing appears as a series of fairly equal “sinusoidal”
of these configurations in this paper; please refer to the primer for waveforms.The inspiratory phase of the breathing cycle is negative or
additional instruction and discussion of the configurations. has an upward position.

A single hose connection of a pressure line from the PTAF2 to a mask Normal breathing
port is the most commonly used configuration.This allows the device
to sense any significant pressure change, as well as flow limitation
caused by partial obstructions.This configuration may open the tracing
to some artifact but is the easiest and most commonly used.

An alternative configuration is the use of a dual hose connection that Flow limitation is the hallmark of RERAs. During the inspiratory phase
utilizes the CPAP tubing in place of a “pneumotach.” This configuration of the breathing cycle the airway becomes unstable and will not let air
can produce an airflow signal of high quality that is comparable to a flow through the airway regardless of effort.This results in a flattening
pneumotach, but does require additional material and set-up time. of the inspiratory waveform, an increase in the inspiratory phase and
a decrease in the amplitude of the waveform.The relative decrease
in amplitude determines whether a given event will be a RERA or a
hypopnea.

If we only look at the temperature flow signal we may miss important
diagnostic information.As we previously discussed, the pressure sensor
is extremely accurate and very sensitive to changes in the airflow.

The single hose mask connection Dual hose connection

It may be helpful to place a one-foot extension of CPAP tubing between the
CPAP unit and the tee.

Understanding the PTAF2 flow tracing

The signals observed during polysomnography come directly from the
body.The accuracy and sensitivity of these signals are important to en-
sure the correct diagnosis. Utilizing pressure to generate the flow
waveforms yields much more information than waveforms generated
using a simple temperature-sensitive device.

This tracing shows flow recorded with Flow limitation is signified by the
a thermistor and flow recorded with a squaring off of the flow signal.
nasal cannula and PTAF2.

10

When scoring sleep recordings, we often see instances where all indi- Flow limitation is a hallmark of RERAs. In some events, if the pressure
cations point to the fact that the person is having an apnea, but we will sensor is not used, the arousal at the end of an event may be scored as
see a significant amount of artifact.We have learned to disregard the a Periodic Limb Movement (PLM) rather than as part of the respiratory
artifact, but may mistake some of the apneas as hypopneas.The PTAF2, event depicted by the flow limitation. Remember: flow limitation is
using nasal pressure to monitor flow, is more straightforward.Apneas seen as a “squaring off” of the sinusoidal waveform usually seen during
will often be demonstrated as straight lines. the inspiratory phase.This squaring off is not seen when using the
thermal sensor.
Hypopneas are clear reductions in flow and may be seen more clearly
when using a nasal pressure sensor. Flow limitation

The flow limitation in the following example is much easier to see and
score using a nasal canula and a pressure sensor.

Obstructive apnea

No sign of flow limitation Top of signal is squared off

Thermistor Sustained flow limitations are particularly common during delta
sleep and may indicate sustained elevated upper airway resistance
without arousal.

Sustained flow limitation
Nasal pressure

Hypopnea

Thermistor

Nasal pressure This is an example of This is an example of sustained
a flow tracing using a flow limitation characterized
thermistor. by the squaring off of the flow
channel using PTAF2.

11

When using a thermal sensor, snoring may be the only indicator that Common issues
partial obstruction is present.The nasal pressure sensor indicates the
flow limitation that is present prior to the arousal and verifies that the Often while recording a sleep study, a few questions or
arousal was clearly associated with respiration. issues may arise. One issue is the loss of inspiratory or
expiratory flow, or a complete loss of the signal.This can
As seen in these examples, the nasal pressure sensor is extremely result from prongs coming out of the nares or, if the prongs
helpful when scoring airflow, especially if the event is ambiguous. are too long, they may lie against the nasal membrane. If
the patient is restless or unable to keep the nasal cannula
Flow limitation with snoring in place, it may be necessary to secure the cannula with
tape. If the prongs are too long, they may be trimmed to
make them more comfortable for the patient and to ensure
a good signal. If the patient has severe rhinorhea, the mucus
may cause a complete blockage of the lumen of the nasal
cannula.This may result in the need to change the cannula.

If the signal is poor or seems chaotic, the filter settings for
the AC amplifier may be incorrect.The highest acceptable
setting is 0.05Hz, or a three second time constant. If the
correct filter settings are not available, a DC amplifier may
need to be used.

snoring PTAF

This is an example of snoring as recorded on a separate channel
and a flow limitation waveform utilizing a PTAF.

12

Frequently asked questions Bibliography

Q. Should I use an AC or DC amplifier? 1. Peppard P,Young T, Palta M, and Skaturd J. Prospective Study of the
A. The choice is yours depending upon availability.The DC amplifier Association Between Sleep Disordered Breathing and Hypertension.
NEJM 2000; 342:1378-84.
is preferred due to slow moving respiratory signals. If the AC
amplifier is used, a very low setting is necessary, such as 0.05HZ 2. Exar EN, Collop NA. The Upper Airway Resistance Syndrome. Chest
or a three second time constant. 115:1127-1139, 1999.

Q. What about oral breathing? 3. Bixler EO,Vgontzas AN, Lin HM, Have TT, Rein J,Vela-Bueno A, Kales A.
A. The oral/nasal prongs may be used to monitor oral breathing.The Prevalence of Sleep-Disordered Breathing in Women – Effects of Gender.
Am J Respir Crit Care Med 163: 608-613, 2001.
tip of the oral cannula should be trimmed to lie where the upper
and lower lips meet.

Q. Can both end-tidal CO2 and the nasal pressure airflow system be 4. Rapoport D, Norman R, Nielson M. Nasal Pressure Airflow Measurement:
used at the same time? An Introduction, Pro-Tech Primer. 2001.

A. Since both end-tidal CO2 and the nasal pressure airflow system 5. Clinical Practice Review Committee,American Academy of Sleep
use a nasal cannula, it would be necessary to use a dual lumen Medicine — Amy L. Meoli MD, Kenneth R. Casey MD, Robert W. Clark
cannula.These are commercially available. MD, Jack A. Coleman, Jr., MD FACS, Robert W. Fayle MD, Robert J.
Troell MD and Conrad Iber MD. Hypopnea in Sleep-Disordered
Q. Does the PTAF2 need to be calibrated? Breathing in Adults. Sleep 24: 469-470, 2001.
A. The PTAF2 requires no periodic calibration, since it is designed to
6. Berg S, Haight JS,Yap V, Hoffstein V, Cole P. Comparison of Direct and
be a “qualitative” device. Indirect Measurements of Respiratory Airflow: Implications for
Hypopneas. Sleep 20: 60-64, 1997.
Q. What should I do if I cannot get a flow or snoring signal?
A. 1. Check all transducer connections to the polysomnograph. 7. Norman RG,Ahmed MM,Walsleben JA, Rapopport DM. Detection of
Respiratory Events During NPSG: Nasal Cannula/Pressure Sensor Versus
2. Verify proper polysomnograph input selections. Thermistor. Sleep 20: 1175-1184,1997.
3. Confirm the polysomnograph sensitivity, filter and sampling
8. Iber, C. et al., The AASM Manual of the Scoring of Sleep and Associated
rates. Events: Rules,Terminology and Technical Specifications.American Academy
4. Check for plugged cannula tips. of Sleep Medicine 2007.
5. Ensure that the cannula is properly positioned on the patient

and connected to the PTAF2.
6. Make sure the batteries are fresh.

Q. What can cause a loss of signal strength during a
recording?

A. 1. The cannula may be displaced.
2. There may be material obstructing the nasal prongs.
3. The sensitivity and filter settings may have been altered.
4. The battery may need replacing.

13

Pulse transit time as a measurement parameter
for respiratory effort and sleep fragmentation

Pulse transit time (PTT) as a measurement parameter Pulse transit time during sleep monitoring
PTT is capable of predicting changes in blood pressure over a short
Introduction period of time. Since the 1970s, PTT has been used in a number of
As the awareness of sleep disorders and the prevalence of sleep- different scenarios as a non-invasive surrogate marker of changes in
disordered breathing have increased, so has the need to accurately blood pressure.
monitor sleep parameters. Polysomnography is the traditional way to
collect multiple parameters of biological data used to determine the PTT refers to the time it takes a pulse wave to travel between two
presence of sleep disorders.The information collected is a direct arterial sites. In other words, PTT is the time between the heartbeat
reflection of physiological activities occurring in various parts of the and the arrival of the blood pressure wave to a peripheral site such
body such as the brain, heart and lungs. as the finger.With the onset of an obstructive apnea, central apnea or
arousal, the patient will have a change in cardiovascular system func-
To detect sleep-disordered breathing, two important aspects of a sleep tioning causing a change to the PTT signal.
study are the measurement of inspiratory effort and arousals. Currently,
the gold standard for measuring inspiratory effort is esophageal pressure In investigations of patients suspected of having sleep-disordered
measurement (Pes).Although esophageal pressure is a quantitative breathing, PTT has recently been proposed as a means of quantifying
measurement that helps detect respiratory effort related arousals respiratory effort by detecting changes in the blood pressure oscilla-
(RERAs), Pes has limitations. It is an uncomfortable, invasive procedure tions associated with pleural pressure swings.The blood pressure
in which an esophageal catheter is passed through the nose and posi- surges associated with micro-arousals can also be detected by PTT,
tioned within the lower third of the esophagus.As a consequence of thus offering the possibility of estimating sleep fragmentations which
having a catheter inserted into the airway, Pes may even contribute to may produce no discernible change in EEG values. PTT has been
sleep disruption.Additionally, this procedure involves setup, requires shown to be a sensitive tool for measuring transient changes in auto-
the skills of a specially-trained technician, and is not conducive to portable nomic tone and has been clinically shown to be equally as accurate as
studies. Due to the invasiveness of Pes, respiratory effort is often cur- esophageal pressure monitoring for measuring respiratory effort in
rently being measured by means that do not sufficiently detect RERAs. frank and subtle respiratory events.3 The number of blood pressure
(BP) rises per hour also correlates well with other indices of
The gold standard for detecting sleep fragmentation and arousals is an sleep fragmentation.4,2
electroencephalogram (EEG) recording which provides the basis for
sleep staging. However, the procedure for setting up EEGs is time con-
suming and difficult to perform outside of the sleep laboratory setting.

Study data has shown that pulse transit time (PTT) can provide a non-
invasive estimate of inspiratory effort and a measure of arousals that
can be used to document obstructive sleep apnea/hypopnea syndrome,
central sleep apnea, RERAs, and response to treatment.2 The following
is a description of PTT and how it may be used to identify and manage
sleep-disordered breathing.

14

Method of measurment When arterial blood pressure falls, vascular tone decreases, which
increases PTT value.Thus, PTT is inversely proportional to blood
Measuring PTT involves the use of an electrocardiogram (ECG) for pressure.4 In this way, PTT gives an indirect measure of blood pressure
the recognition of the R wave and oximetric photoplethysmography with every heartbeat.
(e.g., pulse oximeter) to assess the arrival of the pulse wave in the
periphery. PTT is measured as the interval between the ECG R wave Respiratory effort
and the subsequent arrival of the pulse wave at the finger or ear lobe
(usually the point on the pulse waveform that is 50 percent of the PTT can be used to analyze respiratory effort and define
height of the maximum value).This measurement requires accurate certain respiratory events such as hypopneas, RERAs, etc.
detection of the R wave and the pulse wave (e.g., high sample rate). In adults, there is an excellent correlation between the size
Pulse wave detection is dependent upon a highly reliable pulse of Pes variations and the size of inspiratory-expiratory
oximeter reading.The choice of finger probe or oximeter, therefore, PTT variations.
will determine the accuracy of the PTT measurement.4

maximum Since the heart and large blood vessels are located in the
PTT thoracic cavity, they are affected by variations in thoracic
volume and pressure. During inspiration, the volume of
the thoracic cavity increases, reducing thoracic pressure,
which in turn reduces the compression of the heart, vena
cava, and aorta and results in decreased BP and slow PTT
(PTT dips from the baseline).

50%

minimum

PTT is approximately 200 to 300 ms when using the finger probe and
must be measured to an accuracy of 2 ms.The change in PTT values
occurring within the respiratory cycle is less than 10 ms and with an
arousal, approximately 8 to 15 ms.4

An acute rise in blood pressure causes vascular tone to increase
causing the arterial wall to stiffen, the pressure wave to travel faster
and the PTT to decrease.A transient decrease in PTT is called an
autonomic arousal.At this time, there are no normative values for
these parameters but Pitson and Stradling propose that a decrease
in PTT by 15 ms represents a significant arousal.2

15

Micro-arousal recognition using pulse transit time Recongition of events using pulse transit time

A micro-arousal (MA) is systemically associated with a surge in BP Obstructive events or upper airway resistance episodes may be
causing the PTT to have a transient dip from the baseline or labeled recorded as a steady increase in PTT terminated by an MA followed
PTT.A normal arousal dip usually ranges from 8 to 15 ms in stage I-II by the normalization of the trace, as in the figure that follows. During
sleep, and from 6 to 8 ms during stage III-IV sleep, although there is no central events, PTT reduces in a similar fashion to the reduction in
clear threshold from one patient to another. Therefore, the exact esophageal pressure.4
measurement of PTT change (number of ms) is less impor-
tant than the visual indication.A PTT arousal can be confirmed PTT has been shown to be as accurate as Pes to separate central and
using corroborative signals such as EEG, ECG or BP. obstructive events and to characterize subtle respiratory events.3 It
should be noted that central hypopneas can be judged on the reduc-
Note that during REM sleep, variations in sympathetic nervous system tion in amplitude of PTT proportional to the reduction in flow.4
activity are spontaneously very high and therefore the PTT baseline is Except for Pes, PTT is the only tool validated for the recognition
highly variable.Thus, the recognition of true micro-arousals during of central hypopneas.
REM sleep is less specific than in other sleep stages.4
A pattern of changing and increasing PTT variations followed by a
micro-arousal has been shown to reflect a patient with Cheyne-
Stokes respiration.4

Illustrative obstructive event. In this example, the obstructive nature of the event is
well assessed by the paradoxical movement of thorax and abdomen and progressive
increase in PTT. Obstructive events may be recorded as a steady increase in PTT,
terminated by a micro-arousal, and then the normalization of the tracing.

16

Illustrative central event. In this example, the central nature of the event is well Illustrative PTT signal during obstructive and mixed respiratory events. Notice that
assessed by the proportional decrease in respiratory flow (nasal cannula), there is no airflow in the thermistor channel.The PTT rises in the amount of time
movements of thorax and abdomen, and change in PTT. from the R wave to the pulse so there is an increase in PTT values culminating
when the patient breathes.

In this example, the increases in delta sleep PTT are proportional to the decreases Illustrative RERA episode.The thermistor, thorax and abdomen channels clearly
in Pes and terminated by a micro-arousal (dashed circle) and the normalization show that something is occurring.The progressive increase in esophageal pressure,
of the trace. Because of this proportionality, PTT has a good specificity, sensitivity, with inspiratory flow limitation on nasal cannula, is mirrored by the progressive
and negative predictive value at differentiating obstructive from central apneas increase in delta PTT.The termination of this obstructive respiratory event is
and hypopneas. occurring with the micro-arousal which is well recognized by the transient dip in PTT.
Note also the arterial blood pressure increase at the termination of the event.

17

Limitations of using PTT PTT and CPAP

The major drawback of PTT measurement is a lack of respiratory Because positive pressure therapy will change intrathoracic pressure,
sampling.This is due to the fact that only one value is available per it is logical that PTT measurements may be altered by positive pres-
pulse wave.Therefore, measurements may fall on either side of the sure therapy. Continuous positive airway pressure (CPAP) and bi-level
peak or trough of the BP oscillations associated with respiratory ef- positive pressure used with or without a rate back up should be con-
fort. Under certain conditions, the peak may be missed because the sidered separately.There have been a few physiological recordings of
minimal value of Pes does not happen concurrently with a QRS com- PTT and CPAP or bi-level therapy pressure published to date. Respi-
plex. As a result, a given maximum PTT value may or may not corre- ratory effort was measured using esophageal pressure monitoring and
spond to the lowest point of the Pes.4 PTT while ventilation was evaluated with a pneumotachograph. In this
setting, PTT was found to be a reliable measure of respiratory effort.4
A second drawback of PTT is that a reliable assessment of PTT is not
possible in patients with cardiac arrhythmias.When patients exhibit The following graph shows that PTT works well with PAP therapy.
atrial fibrillation or extra systolic activity, misinterpretation of PTT
trace is possible. Since the PTT measurements begin with the R wave
on the ECG, false values of PTT occur when the patient suffers from
cardiac arrhythmia. Extra systole produces acute variations in PTT de-
spite the absence of a respiratory event or MA.4

Recurrent obstructive events occurring on bi-level ventilation support.

Cardiac arrhythmia presence requires Summary
particular attention as false PTT values
can be mistaken for respiratory efforts. PTT measurement is shown to be a reliable method of
determining arousals and microarousals in patients while
they are undergoing a polysomnographic evaluation.Accu-
racy of PTT assessment is dependent upon the choice of
equipment, the evaluator’s understanding of the wave-
forms and the evaluator’s interpretation of the data.

18

Bibliography
1. Marin, Jose M., Carrizo, Santiago J.,Vicente, Eugenio,Agusti Alvar

G.N. Long-Term Cardiovascular Outcomes in Men with Obstructive Sleep
Apnea-Hypopnea With or Without Treatment With Continuous Positive
Airway Pressure:An Observational Study.The Lancet 2005;365: 1046-1053.
2. Pitson, DJ., Stradling JR.Value of Beat-to-Beat Blood Pressure
Changes, Detected by Pulse Transit Time, in the Management of the Ob-
structive Sleep Apnea/Hypopnea Syndrome. Eur Resp J 1998;12: 685-
692.
3. Pepin, Jean-Louis, Delavie, Nadege, Pin, Isabelle, Deschaux, Chrystele,
Argod, Jerome, Bost, Michel, Levy, Patrick. Pulse Transit Time Improves
Detection of Sleep Respiratory Events and Microarousals in Children.
Chest 2005;127: 722-730.
4. Tamisier, R., Pepin, JL, Levy, P. Pulse Transit Time. Physiology and Sleep
Laboratory, University Hospital, Grenoble, France.

19

An introduction to respiratory
inductance plethysmography

Background Changes in lung volume are most accurately measured using spirometry
equipment, in which lung volumes (e.g.,Tidal Volume) and flow rates
In a polysomnographic study, a variety of physiologic pa- (via a flow loop) are determined by having the patient breathe through
rameters must be measured. One of the most important a closed tube.The tube simultaneously records volume and flow changes
parameters measured is breathing. Breathing, and breathing during the breath. Spirometry typically requires a sealed nasal airway
events, can be assessed by measuring nasal and/or oral air- which allows airflow to move only through the mouth. In order to
flow in tandem with chest and abdominal wall movement. obtain this measurement the patient must make a conscious effort to
create a consistent type of breathing pattern.Therefore, it is impractical
While the above criteria are fairly straightforward in defi- for use in clinical polysomnography.
nition, the actual physiological assessment of breathing can
be challenging.The essential task is to demonstrate effort, There are three primary methods of noninvasive chest and abdominal
or lack of effort, to breathe in addition to the absence of, plethysmography (measurement of change in volume) currently in use
or significant change in, airflow. within the sleep center: 1) measurement of changes in elastic belt
tension (elastometric); 2) measurement of changes in electrical
impedance (impedence); and 3) measurement of changes in electrical
inductance (respiratory inductance).

Measuring respiratory effort Elastometric plethysmography
There are a variety of methods currently used in polysomnography In elastometric plethysmography, an elastic belt is fastened around the
to evaluate respiratory effort. One of the most accurate methods of chest or abdomen which will exhibit a change in tension as the chest
measuring respiratory effort is esophageal manometry. Esophageal or abdomen expands or contracts.This change in tension is easily
pressure (Pes) is measured by having the patient swallow a pressure measured and converted to a voltage by a variety of methods.The
catheter which then resides in the esophagus throughout the sleep most common method used for identifying the change in tension is a
study. Rhythmic fluctuations in thoracic pressure in the absence of piezo-electric sensor.A piezo-electric sensor is a crystal that directly
significant nasal and oral airflow are the best “proof” of the presence generates a voltage when compressed or stretched.This method, while
of obstructive apnea. In clinical practice however, the procedure to simple and inexpensive, is subject to “trapping artifact”. It is fairly easy
obtain the esophageal pressure measurements is very uncomfortable to imagine how a portion of elastic belt may become “trapped” as a
for most patients and is therefore not used routinely. person turns from one side to another, resulting in variable tension
along the belt circumference.Thus this method can both significantly
Another surrogate measure of respiratory effort can be obtained by under and/or overestimate the actual degree of chest or abdominal
measuring changes in chest and/or abdominal volume, known as movement.Additionally, it may create a false signal when belt tension
plethysmography. Plethysmography helps to determine if the patient suddenly changes with a change in body position.
stops breathing or has alterations in his/her breathing during sleep,
and the frequency of the changes occurring throughout the study.

20

Impedance plethysmography Historical considerations
The human body is a fairly poor conductor of electricity. In other Respiratory Inductance Plethysmography was initially developed as a
words, it presents a fairly high impedance to electrical current flowing tool to noninvasively measure respiratory volumes and was used
through it.This impedance changes as the cross-section of the body primarily in pediatric and veterinary asthma research. It was adapted
expands or contracts.While a patient’s abdomen or thorax expands for human polysomnography in the 1990s, and its use has rapidly
and contracts during breathing, qualitative measurement of changes in increased as patents on the technology have expired and associated
electrical impedance during breathing will identify the patterns of costs have come down.
breathing.Two (or sometimes more) electrodes are attached to the
skin.A weak alternating electrical current is passed through these Technical considerations
electrodes, allowing the impedance to be measured.This method RIP equipment consists of the following:
yields a non-linear signal, which is useful only as a qualitative measure 1. Effort belt, consisting of an elastic material with a zigzagging
of chest or abdominal movement. Given that an electrical current
must be passed through the body, care must be taken to choose a (coiled) wire sewn into the belt.
frequency range that would not interfere with other monitoring 2. Connecting wire sets.
equipment or with implanted equipment such as pacemakers or 3. Driver module consisting of a frequency generator, signal processor
defibrillators.
and analog/digital converter.

Respiratory Inductance Plethysmography (RIP)
Respiratory Inductance Plethysmography relies on the principle that a
current applied through a loop of wire generates a magnetic field normal
for that orientation of the loop.Any change in the area enclosed by
the loop creates an opposing current within the loop directly propor-
tional to the change in the area.With a RIP system, a zigzagging coiled
wire is sewn into an elastic belt.This allows for expansion and contraction.
This belt can be worn around the chest or abdomen.An alternating
current (AC) is passed through the belt, generating a magnetic field.
The frequency of the AC is set to be more than twice the typical
respiratory rate in order to achieve adequate sampling of the respiratory
effort waveform.The act of breathing changes the cross-sectional area
of the patient’s body.This changes the shape of the magnetic field gen-
erated by the belt, inducing an opposing current that can be measured
most easily as a change in the frequency of the applied current.With
RIP, no electrical current passes through the body; a weak magnetic
field is present but does not affect the patient or any surrounding
equipment.The signal produced is linear and is a fairly accurate repre-
sentation of the change in cross-sectional area. In addition, RIP does
not rely on belt tension and is not affected by belt trapping.

21

Applications of respiratory inductance plethysmography The summing channel can also be thought of as an indicator of the
phase relationship of the chest and abdominal belts.The more “out of
RIP can be used in tandem with nasal/oral airflow to produce a flow- phase” the signals are becoming (moving toward paradox), the smaller
volume loop (see picture 1).This technique can be employed to assess the sum channel will be.When expansion and contraction of the chest
inspiratory and expiratory flow limitation as a function of body position, and abdomen are completely out of phase, the sum channel will be
sleep stage, etc. flat (see figure 2). However, due to the method by which the sum
channel is created, a completely flat sum signal is rare due to the delay
Expiration in the summing and normalization of the channels in the summing
process.The sum signal does, however, serve a very useful function by
showing a definite decrease in the signal amplitude during paradoxical
breathing events.

Inhalation Figure 1: Normal flow-volume Recording RIP effort signals
Flow-volume loop loop of patient during expiration
and inhalation. When recording Respiratory Impedence Plethysmography through an
AC channel the following settings should be used:

The chest and abdominal signals provided by the RIP belt can be Low frequency filter 0.1 Hz or lower (0.05 - 0.01 Hz)
represented independently, or they can be mathematically summed. (High pass filter) 0.1 Hz or lower (0.05 - 0.01 Hz)
Mathematical summing of the signals is particularly useful as a screen for (Time constant) 1.0 Sec or longer (3 - 5 Sec)
paradoxical breathing. Because there are differences in the amplitudes
of chest and abdominal output signals, these values are typically Using a low frequency setting of 0.05 to 0.01 Hz can allow visualization
normalized prior to summation. of possible flattening in the thorax belt which sometimes occurs along
with a flattening of the observed signal from a pressure transducer.

Figure A High frequency filter 35 Hz
(Low pass filter) 35 Hz

Figure B

Figure C

Figure D

Figure 2: Figure A shows normal breathing.
Figure B demonstrates what occurs during phase shifting, which is causing
the sum channel to show alterations in the waveform.
Figure C and D demonstrate what occurs with a patient who is having
paradoxical breathing at night, causing the sum channel to be flat.

22

An average resting respiratory rate is 12 breaths per minute.This is Another consideration is belt placement. For example, if a RIP effort
equal to approximately 0.2 Hz.A relatively low setting of the high belt is placed around the hips, there will be little to no change in the
frequency filter (low pass filter) should not influence this signal. cross-sectional areas during diaphragmatic excursions.To ensure
quality signals, RIP belts should be placed at the standard locations:
Sampling rate 10 Hz or higher near the nipple line (or mid-chest) and just above the belly button.

This figure shows Waveform samples
how the RIP belts can
parallel the output of Note the flattening of the “chest” signal that occurs simultaneously
a pressure transducer with the “snore” signal.
used to measure
flow.

Comparing RIP to piezo crystal effort belts Note the flattening of the “chest” signal that occurs simultaneously
The sensing element on a piezo effort belt is a peizo cyrstal.This is with the “snore” signal.
a silicone element that generates an electric signal when a force is
applied. It is only located on a very small section of the belt.There are (C3)-(A2)
situations, when a patient is lying on top of the piezo crystal, in which (C4)-(A1)
the effort signal can be dampened or not detected.This may produce (O1)-(A2)
erroneous readings or unexplained changes in polarity that look like (O2)-(A1)
paradoxical effect. For these reasons, RIP effort sensors have been (LOC)-(A2)
identified as superior to piezo effort crystals.1 (ROC)-(A1)
(S CHIN1)-(S CHIN2)
Poor signals (EKG1)-(EKG2)
RIP technology has been shown to be very accurate in determining the Snore
effort of breathing. However, there are conditions that can decrease P FLOW
the accuracy of a RIP device. If the belts are placed too tight, causing Ch+Ab-Sum
the actual cross-sectional change of the chest or abdomen to be Chest
restricted, it will not reflect the patient’s true breathing efforts. If the Abdomen
belts are placed too loosely, the belts will have a tendency to move SaO2-Nel
and may overlap one another.
Cardio-ballistic artifact in “pressure/flow” signal.

23

(C4)-(A1) Setting up the patient and fitting the belt
(O2)-(A1)
(LOC)-(A2) When setting up a RIP system, first check to ensure you have all the
(ROC)-(A1) components.The system components include the RIP effort sensor,
(S CHIN1)-(S CHIN2) wireset and module.Two RIP effort sensors are typically used with
P FLOW each patient, one for the thorax and one for the abdomen. RIP wiresets
Ch+Ab-Sum are used to connect the RIP effort sensors to the RIP module which
Chest is then connected to the physiological recorder. However, some
Abdomen physiological recorder systems may accept the RIP effort sensors
SaO2-Nel without the use of the RIP module.
SaO2
Placement and adjustment of the RIP system
If this was UARS, there would be a shift in the phase between the The RIP effort sensors should be placed comfortably, and securely,
“chest” and “abdomen” signals. around the abdomen and thorax.When stressed by the expansion and
contraction of respiration, the sensors generate a voltage signal which
P FLOW provides a respiratory effort tracing on a physiologic recorder.When
applying the RIP system on a patient, adjust each belt to accommodate
Ch+Ab-Sum the size of the patient, making sure the belt is not too tight or confining.
A belt that is too tight will not be able to provide an accurate reflection
Chest of the patient’s breathing patterns.

Abdomen Adjustments (figure 3)

SaO2-Nel To lengthen the belt:
Hold the male buckle, pull the inner layer of the loop down and away
“Abdomen” and “chest” inputs connected with reversed polarity. Make from the buckle, then grasp the belt past the slide lock and pull them
certain the same inputs are used for Grid 1 and Grid 2. Reference and apart until the loop is flat.
signal inputs must be connected with the same polarity.
To shorten the belt:
SaO2 Hold the slide lock and pull the inner layer of the loop toward the
(l-EOG)-(A2) male buckle, then grasping the slide lock and the male buckle, pull
(R-EOG)-(A1) them apart until the loop is flat. Snap buckles together in the front.
(C3)-(A2) Adjust the belt so that it is secure, but not overly tight.To loosen the
(C4)-(A1) belt, grasp the slide lock and lift slightly away from the patient while
(O1)-(A2) pulling towards the loop.To tighten the belt, grasp the slide lock and
(O2)-(A1) pull away from the loop while repeatedly grasping and pulling the
(EMG1)-(EMG2) outer layer of the loop toward the slide lock.
Snore
(EKG1)-(LEG1)
(LEG1)-(LEG2)
PFLow
Airflow
Chest zRIP
Abdomen zRIP

Figure 3: Adjust as above.

24

Once the system is placed correctly around the abdomen and thorax, Cleaning the system
plug the 1.5 mm end of the wireset into the belt near the buckles. Plug Belts can be washed using warm water and household detergents.The
the other end, with a 249 connector, into the designated inputs on the belts should be air dried. Care should be taken to ensure drying of
zRIP module (figure 4). Plug the output channels into inputs of your the safety plugs after cleaning. Do not clean the belts with alcohol
polygraph.You can check proper placement of the system through an or alcohol-based product. Do not place the belts into the washing
external testing system. In addition, calibration of the system should machine or other system that may damage the internal wires during
occur to ensure proper measurement of the abdominal and thorax the cleaning process.
movement and summing.
The wire set may be wiped down with soapy water, bleach or an
alcohol towelette. Do not immerse the wire set into liquids.

Identification and scoring of respiratory inductance belts
An important task in scoring and interpreting a polysomnogram is
assessing whether an apnea is present. It is also important to distinguish
what may be the cause of the apnea: central apneas vs. obstructive
apneas vs. mixed apneas.When the American Academy of Sleep
Medicine released its new scoring guidelines in 2007, it recommended
using either esophageal manometry or Respiratory Inductance
Plethysmography for the measurment of respiratory effort.1 The following
outlines the AASM guidelines for apnea, hypopnea and RERA's.

Figure 4: Plug the 249 connector into the designated inputs on the Per the 2007 guidelines, all of the following criteria must be met in
zRIP module. order to score an apnea1:
1. There is a drop in the peak thermal sensor excursion by ≥ 90%
Instrument settings sensitivity – Approximately 50µV/mm.Adjustment
of the sensitivity up or down is typically required. Response is depend- of baseline.
ent upon such variables as sensor application and patient effort. 2. The duration of the event lasts at least ten seconds.
Low frequency filter/time constant – 0.16 Hz (or 1 second or longer). 3. At least 90% of the event’s duration meets the amplitude
Shorter time constants or higher low frequency filter settings will
significantly attenuate waveforms. High frequency filter – 35 Hz. reduction criteria for apnea.

In addition, classification of apnea in an adult also needs to include the
type of respiratory effort that accompanied the changes in airflow:1
1. Score a respiratory event as an obstructive apnea if it meets

apnea criteria and is associated with continued or increased
inspiratory effort throughout the entire period of absent airflow.
2. Score a respiratory event as a central apnea if it meets apnea
criteria and is associated with the absence of inspiratory effort
throughout the entire period of absent airflow.
3. Score a respiratory event as a mixed apnea if it meets apnea
criteria and is associated with a lack of inspiratory effort in the
initial portion of the event, followed by resumption of inspiratory
effort in the second portion of the event.

25

For scoring a hypopnea when the nasal pressure device is not functioning, With respect to a respiratory effort-related arousal (RERA), use of
alternative sensors including uncalibrated or calibrated inductance esophageal pressure is the preferred method of assessing change in
plethysmography or an oronasal thermal sensor may be used.The respiratory effort, although nasal pressure and inductance plethysmog-
rules also state “classification of hypopnea as obstructive, central or raphy can be used.To score a RERA there is a sequence of breaths
mixed should not be performed without a quantitative assessment lasting at least ten seconds characterized by increasing respiratory
of ventilatory effort, which includes calibrated respiratory inductance effort or flattening of the nasal pressure waveform leading to an
plethysmography.” arousal from sleep when the sequence of breaths does not meet
criteria for an apnea or hypopnea.
To score a hypopnea, all of the following criteria are recommended
and must be met:1 Conclusion
1. The nasal pressure signal excursions (for those of the alternative
Identification of respiratory effort is critical in determining
hypopnea sensor) drop by greater than 30% of baseline. what is occurring with a patient undergoing a polysomno-
2. The duration of this drop occurs for a period lasting at least gram. Respiratory Inductance Plethysmography is an alter-
native method of identifying changes in breathing patterns.
ten seconds. Appropriate identification, and understanding of changes
3. There is a 4% or greater desaturation from the pre-event baseline. in breathing patterns, will enable the sleep technician to
4. At least 90% of the event's duration must meet the amplitude observe sleep-disordered breathing events.This should lead
to effective treatment recommendations for the patient.
reduction of criteria for a hypopnea.

An alterative option for scoring hypopnea's include:
1. Nasal pressure signal excursions (or those of the alternative

hypopnea sensor) drop by 50% or greater of the baseline.
2. The duration of the drop occurs for a period of at least ten seconds.
3. There is a 3% or greater desaturation from pre-event baseline or

that the event is associated with an arousal.
4. At least 90% of the event’s duration must meet the amplitude

reduction of criteria for a hypopnea.

26

Bibliography
1. Iber, C. et al.,The AASM Manual of the Scoring of Sleep and Associated

Events: Rules, Terminology and Technical Specifications.American
Academy of Sleep Medicine 2007.

27

Notes

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Course title: An introduction to diagnostic equipment for the sleep technologist

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Identify the benefits of RIP, PTT and PTAF

Identify various methods to determine respiratory
effort with patient undergoing PSG

Identify reasons for using RIP, PTT and PTAF

Identify the technical considerations while using RIP, PTT and PTAF

Identify how to apply and troubleshoot RIP, PTT and PTAF

Identify set up, cleaning and care of the RIP system, PTT and PTAF

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Post-test: evaluating airflow using a nasal pressure transducer

Indicate the answer using blue or black ink for each of the following questions.

1. Which of the following may affect the airflow signal when using 3. What type of amplifier can be used with a pressure sensing
a thermal-based sensor? device?

A. Having a fan directed at the patient. A. AC amplifier

B. Using a positive pressure device. B. DC amplifier

C. The room is too hot – very little temperature difference C. No amplifier is necessary
between the room air and the exhaled air. D. Both an AC and a DC amplifier

D. All of above

2. Match the description to the tracing 4. The nasal cannula with a pressure transducer may be used with
(figure number): a positive pressure device.

True___ False___

figure 1 5. Which figure is an unfiltered signal?
figure 2 A _______
B _______

figure 3 figure A
A. Change in the morphology or squaring-off
figure B
of the airflow signal – flow limitation.
Figure ____________ 6. Nasal prongs used with the PTAF 2 system may be trimmed to
optimize the signal and ensure proper placement and fit.
B. Periodic lapse of airflow signal – apnea. True___ False___
Figure ____________
7. On the DC amplifier, the low-frequency filter must be set
C. Periodic decrease in the amplitude of airflow correctly to visualize snoring.
signal – hypopnea. True___ False___
Figure ____________

Post-test: pulse transit time as a measurement parameter
for respiratory effort and sleep fragmentation

Indicate the answer using blue or black ink for each of the following questions.
1. What is PTT?

A. Time taken for a pulse wave to travel between two arterial sites
B. A measurement of transient changes in autonomic tone
C. A measurement requiring ECG and pulse wave detection
D. All of the above
2. Increased BP (increases, decreases) vascular tone and (shortens, lengthens) PTT.
3. Decreased BP (increases, decreases) vascular tone and (shortens, lengthens) PTT.
4. PTT has been shown to be as accurate as Pes to separate central and obstructive
events and to characterize subtle respiratory events.True___ False___
5. A typical PTT would be 350ms with an accuracy of +/- 2 ms.True___ False___
6. Pulse wave detection is dependent upon a highly reliable pulse oximeter reading.
True___ False___
7. Visual analysis of PTT is NOT a good tool for distinguishing central and
obstructive events.True___ False___
8. PTT is easy to measure, inexpensive, noninvasive and fully portable.True___ False___
9. The recognition of true micro-arousals during REM sleep using PTT is less specific than in
other sleep stages.True___ False___
10. In the figure below, central (plain lines), obstructive (dash lines) and mixed events coexist.
In these circumstances PTT is reliable and helpful for scoring.True___ False___

SaO2 (%)

Thermistor

Thorax

Abdomen

Nasal
Cannula

PTT

Post-test: an introduction to respiratory inductance
plethysmography

Indicate the answer using blue or black ink for each of the following questions.

1. An average resting respiratory rate is 12 breaths per minute.
True___ False___

2. The sensing element on a RIP effort belt, a zigzagging wire, runs the entire length of the belt.
True___ False___

3. Name 3 primary methods of noninvasive chest and abdominal plethysmography:
1) _________________________
2) _________________________
3) _________________________

4. The best place to place a RIP effort belt is around the hips.
True___ False___

5. Two RIP effort sensors are typically used with each patient.
True___ False___

6. Belts should be air dried versus putting them in the dryer.
True___ False___

7. Esophageal manometry is not one of the most accurate methods of measuring respiratory effort.
True___ False___

8. Spirometry equipment is used to most accurately measure changes in lung volume.
True___ False___

9. In elastrometric plethysmography, the most common method of identifying change in
tension is a piezo-electric sensor.
True___ False___

10. Inductance plethysmography was adapted for human plethysmography in the 1970s.
True___ False___

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+41 6 27 45 17 50
Europe, Middle East,Africa Respironics Australia
+49 7031 463 2254 +61 (2) 9666 4444 Respironics United Kingdom
+44 800 1300 845
Latin America Respironics Deutschland
+55 11 2125 0744 +49 8152 93 06 0 www.philips.com/respironics

North America Respironics Europe, Middle East,Africa
+1 425 487 7000 +33 1 47 52 30 00
800 285 5585 (toll free, US only)

Respironics, Pro-Tech, PTAF, Pro-Flow,Alice, and zRIP are trademarks of Respironics, Inc. and its affiliates.
All rights reserved.

©2009 Koninklijke Philips Electronics N.V.All rights are reserved.
Philips Healthcare reserves the right to make changes in specifications and/or to discontinue any product at any time without notice or
obligation and will not be liable for any consequences resulting from the use of this publication.
CAUTION: US federal law restricts these devices to sale by or on the order of a physician.
Geyer SB 05/29/09 MCI 4102466 PN 1052673