The capnometer, oximeter, and incentive inspirometer provide complementary information. A capnometer measures end-tidal CO2. An oximeter monitors oxygen saturation from a digit or earlobe. Finally, an incentive inspirometer calculates the volume of air inhaled in a single breath.
Note that a thermistor can detect the 2°–5° F temperature shift from inhalation to exhalation when positioned in a nostril's airstream in a 70°–75° F room (Gilbert, 2019).
BCIA Blueprint Coverage
This unit addresses III. HRV Instrumentation: C. Respirometer and D. Accessory SEMG.
This unit covers the Respirometer, Surface Electromyograph, Capnometer, Oximeter, Incentive Inspirometer, Normal Values, and Drug Effects.
Please click on the podcast icon below to hear a full-length lecture.
Figure caption. One-minute recording of respiration in which the subject breathes more thoracically (indicated by the larger amplitude of the black thoracic tracing and the ratio of the abdominal/thoracic standard deviations: 3.34/4.40 = 0.76).
Respirometers Can Identify Dysfunctional Breathing
A respirometer can help identify and retrain dysfunctional breathing behaviors like apnea, clavicular breathing, gasping, reverse breathing, sighing, and thoracic breathing (Peper et al., 2016).
Respirometers Can Help Measure HR Max - HR Min and Resonance Frequency
In heart rate variability (HRV) biofeedback, a respirometer enables us to measure HRV and determine a client's resonance frequency. Since a respirometer monitors the respiratory waveform, the software can calculate when each breathing cycle starts and stops. This allows us to measure the HRV time-domain metric HR Max – HR Min, the mean difference between the highest and lowest heart rates during each respiratory cycle.
A respirometer is also indispensable in determining a client's resonance frequency, which is the rate that best stimulates their cardiovascular system (Shaffer & Meehan, 2020).
How Respirometers Work
Current is run through a respirometer, resistance changes as the band stretches, and the output voltage is proportional to length changes. The amplified voltage is displayed in relative units of stretch (RUS) from 0-100 (Peper et al., 2016; Shaffer & Combatalade, 2013).
We can only compare two waveforms when their respirometers share a similar range (e.g., 3 units of signal change per 5 mm of stretch) and are displayed using the same lower and upper values on the vertical axis. Peper et al. (2016) provide a detailed description of sensor calibration.
Clinicians should be cautious when comparing measurements across sessions using the same abdominal and thoracic sensors. Since peak values depend on the exact placement of the band,
the constrictiveness and thickness of the clothing under the band, and band tension, reliability can be very low (Shaffer & Combatalade, 2013).
A Mind Media respirometer is shown below.
Below is a
BioGraph ® Infiniti display of abdominal movement.
Note the slow rhythmic breathing pattern.
Sensor Placement
Since constrictive clothing can impede abdominal and chest expansion, clinicians should instruct clients to avoid wearing a "...tight belt, slimming underwear, constrictive pants, or a very tight bra" (MacHose & Peper, 1991; Peper et al., 2016).
Artifact
Avoid thick clothing (e.g., sweaters) because it can compromise accuracy and promote upward or downward slippage. Tape or pin the respirometer to your client's clothing to prevent slippage artifacts (Gilbert, 2019).
Since belly contours vary greatly, place the abdominal respirometer above the navel within a horizontal zone that expands during inhalation (Gilbert, 2019).
To ensure adequate sensor responsiveness, ask your client to exhale completely and then slightly tighten the sensor
band during the post-expiratory pause. Avoid tightness extremes. A respirometer that is too tight can curtail spontaneous breathing, while one that is too loose can overlook small abdominal or chest excursions (Gilbert, 2019).
You want to see a sinusoidal signal pattern with sufficient amplitude to detect the peaks and valleys.
Limitations of Respirometer Displays
Review the raw respirometer waveforms for responsiveness to abdominal and thoracic excursion, dysfunctional breathing behaviors, and smoothness. Numeric displays of abdominal movement and respiration rate may look correct, while end-tidal CO2 and HRV are reduced by excessive effort (Shaffer, Bergman, & Dougherty, 1998).
Tracking Test
By performing a tracking test, you can determine whether a respirometer display mirrors your client's abdominal movement. Instruct your client to inhale and then exhale, and check whether the abdominal waveform mirrors stomach movement.
If you question the accuracy of respiration rate measurements, visually count the number of abdominal or chest excursions over one minute.
Below is a
BioGraph ® Infiniti display of an abdominal respiratory band tracking test.
Normal Values
Typical resting adult respiration rates are between 12-14 bpm (Khazan, 2019). Following a stressor, clinicians may measure elevations above baseline and the time required to recover to baseline values (Khazan, 2013, p. 46).
Evaluate the raw signal for ECG artifact, which may be superimposed on the SEMG signal. You can minimize the risk of this artifact by using a narrower bandpass and closer electrode spacing.
The BioGraph ® Infiniti screen below provides respiratory
and SEMG biofeedback to teach rhythmic breathing while maintaining
relaxed accessory muscles.
Note the overuse of accessory muscles during clavicular breathing.
Oximetry
A pulse oximeter utilizes a photoplethysmograph (PPG) sensor to measure blood
oxygen saturation from a finger or earlobe. Oximeters compare the ratio of red and blue wavelengths in the blood to measure hemoglobin oxygen transport. During HV or overbreathing, oxygen saturation (PaO2) may approach 100%. PaO2 values over 98% signal that less O2 and nitric oxide are available for body tissues (Gilbert, 2019). A Mind Media oximetry sensor is shown below.
Oximetry can reassure clients anxious about suffocating that they are receiving sufficient oxygen. Oximetry can also detect abnormally low saturation (≤ 85%) due to compromised circulation or emphysema (Gilbert, 2019).
Racial Bias
Physicians use oximetry to identify patients who need supplemental oxygen. Since this technology was developed using a racially non-diverse population, it should not be surprising that occult hypoxemia (undetected blood oxygen levels below 88%) was three times more likely in Black than White patients in two large cohorts.
Caption: Accuracy of Pulse Oximetry in Measuring Arterial Oxygen Saturation, According to Race. Shown is a comparison of paired measurements of pulse oximetry readings of oxygen saturation and time-matched directly measured arterial oxygen saturation among hospitalized patients who were stratified according to race. The shaded area indicates an arterial oxygen saturation of less than 88%. In the box plot, the horizontal line within each box represents the median. The top and bottom of each box represent the upper and lower limits of the interquartile range. The whiskers represent 1.5 times the interquartile range. Data points indicate outliers outside this range.
Artifact
Finger vasoconstriction due to cold exposure or sympathetic activation can prevent accurate measurement. Review the unit on Cardiovascular Instrumentation for possible solutions. Excessive variability in the time between heartbeats can also compromise oximeter measurements due to irregular pulse pressure (Gilbert, 2019).
Normal Values
Oxygen saturation between 95-98% is normal at sea level for healthy individuals. Saturations of 95-98% are better than 100% because “it means there’s a bit more oxygen in the bloodstream and a bit less in the tissues, which is the only place where it can do any good” (Gilbert, 2012, p. 138).
Consider this analogy: A truck is delivering groceries to a grocery store, and people in the store are waiting to buy those groceries. But the truck doors are only partly open, allowing only a few groceries to be unloaded and placed on the shelves. There are plenty of groceries in the truck, but not enough groceries in the store. That’s what happens with extra-high O2 saturation. The oxygen cannot perform its function in the bloodstream; it has to be released to the issues (Gilbert, 2012, p. 138).
When SpO2 exceeds 98%, the additional oxygen is primarily dissolved in the plasma. This can produce oxidative stress, vasoconstriction, and tissue injury, especially in critically ill patients. While 100% SpO2 is not harmful in brief or healthy contexts (e.g., post-exercise recovery), in many clinical settings, 99% is preferred to avoid excessive oxygen exposure. The ideal range is 95-98%.
100% oxygen saturation is not better than 98% saturation because the additional oxygen is dissolved into the plasma, where it can harm vulnerable patients.
For most adults receiving supplemental oxygen, the preferred target oxygen saturation (SpO2) is 94–98%, according to major clinical guidelines (O'Driscoll et al., 2017).
A lower target of 88-92% is recommended in chronic obstructive pulmonary disease (COPD) to avoid suppressing the hypoxic respiratory drive or worsening acidosis. (Echevarria et al., 2021).
Levels below 90% may indicate dysfunctional breathing or life-threatening medical conditions like emphysema (Gilbert, 2012).
Capnometer
A capnometer monitors end-tidal CO2, the percentage of CO2 in exhaled air at the end of exhalation.
A reading of 36 mmHg corresponds to about 5% CO2 in exhaled air. Resting end-tidal CO2 values between 35-45 mmHg are normal, 30-35 mmHg indicate mild-to-moderate overbreathing, 25-30 mmHg show moderate-to-severe overbreathing, and below 25 mmHg signal severe overbreathing (Khazan, 2013, pp. 46, 80).
Since John's PO2 is 96%, he plans to increase it to 99% since
he believes higher values are better. What did John forget?
When SpO2 exceeds 98%, the additional oxygen is primarily dissolved in the plasma. This can produce oxidative stress, vasoconstriction, and tissue injury, especially in critically ill patients. While 100% SpO2 is not harmful in brief or healthy contexts (e.g., post-exercise recovery), in many clinical settings, 99% is preferred to avoid excessive oxygen exposure. The ideal
range is 95-98%.
Glossary
capnometric biofeedback: the display of end-tidal CO2 back to the monitored individual.
end-tidal CO2: the percentage of CO2 in exhaled air at the end of exhalation.
HR Max-HR Min: a heart rate variability time-domain metric that calculates the average difference between the highest and lowest heart rates during each respiratory cycle.
incentive inspirometer: a calibrated cylinder with a piston that moves upward as the patient
inhales and indicates the volume of air inhaled in a single breath (the incentive).
photoplethysmographic (PPG) sensor: a photoelectric transducer that transmits and detects infrared
light that passes through or is reflected off tissue to measure brief changes in blood volume and detect the
pulse wave.
pulse oximeter: a device that measures dissolved oxygen in the bloodstream
using a photoplethysmograph sensor placed against a finger or earlobe.
resonance frequency: the frequency at which a system, like the cardiovascular
system, can be activated or stimulated.
respirometer: a sensor that changes resistance to a
current as it expands and contracts during the respiratory cycle.
slippage artifact: the upward or downward movement of a respirometer, often due to thick underlying clothing.
surface EMG (SEMG): muscle action potentials, detected by surface electrodes
placed over skeletal muscles, back to the monitored individual.
thermistor: a temperature-sensitive resistor.
torr: a unit of atmospheric pressure, named after Torricelli, which equals 1 millimeter of mercury
(mm Hg) and is used to measure end-tidal CO2.
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Visit the BioSource Software Website
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For Biofeedback, BioSource Software offers Human Physiology to satisfy BCIA's Human Anatomy & Physiology requirement. For Neurofeedback, BioSource provides Physiological Psychology to satisfy BCIA's Physiological Psychology requirement.
BCIA has accredited each course, and they combine affordable pricing ($150) with industry-leading content.
Essential Skills
1. Explain the respiration signal, healthy breathing, and biofeedback to a client.
2. Explain sensor attachment to a client and obtain permission to monitor her.
3. Explain how to select a placement site and demonstrate how to attach a respiration sensor to the chest and
abdomen. Show how to monitor the accessory muscles to measure breathing effort.
4. Perform a tracking test asking your client to take a slow deep breath.
5. Identify breath-holding, gasping, and movement artifacts in the respiration signal and how to remove them from
the raw data.
6. Explain how to identify clavicular breathing, excessive breathing effort, reverse breathing, and thoracic
breathing.
7. Explain how posture and clothing can affect breathing.
8. Demonstrate how to find your client's resonance frequency and explain why this is important.
9. Demonstrate how to instruct a client to utilize a breathing pacer and the feedback display.
10. Discuss strategies for slowing your client's breathing toward 5-7 breaths per minute.
11. Demonstrate a respiratory biofeedback training session, including record keeping, goal setting, site
selection, baseline measurement, display and threshold setting, coaching, and debriefing at the end of the
session.
12. Demonstrate how to select and assign a practice assignment based on training session results.
13. Evaluate and summarize client progress during a training session.
Assignment
Now that you have completed this module, describe the method you use to
monitor client breathing and the types of measurements you record. If
you use a strain gauge to measure breathing, where do you place the
strain gauge and why? What precautions do you take when attaching the
strain gauge to female clients?
References
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Fried, R. (1987). The hyperventilation syndrome: Research and clinical
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Gilbert, C. (2019).
A guide to monitoring respiration. Biofeedback, 47(1), 6-11. https://doi.org/10.5298/1081-5937-47.1.02
Khazan, I. Z. (2013).
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Peper, E., Groshans, G. H., Johnston, J., Harvey, R., & Shaffer, F. (2016). Calibrating respiratory strain gauges: What the numbers mean for monitoring respiration. Biofeedback, 44(2), 101-05. https://doi.org/10.5298/1081-5937-44.2.06
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https://doi.org/10.3389/fpubh.2017.00258
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