Breathing is continuous. Most clinical assessments of it are not. Spirometry and other clinical tests capture respiratory function in a single session, under instruction, at one moment in time.
Many of the respiratory characteristics that matter to patients happen outside those moments: coughing through the night, pauses in breathing, or respiratory patterns that shift over days. Wearable sensors make it possible to measure some of those characteristics where they happen.
Which Respiratory Measures Can Wearable Sensors Capture?
Wearable sensors can capture respiratory rate, breathing patterns including apnea events, estimates of respiratory volume and cough frequency. Which of these a study can collect depends on the sensor, where it is worn and the population.
Respiratory Rate
Respiratory rate is the number of breaths per minute. According to a StatPearls review on NCBI Bookshelf, the normal adult range is 12 to 20 breaths per minute. Wearable sensors can estimate respiratory rate at rest, during activity or during sleep, depending on the sensor and how it is worn.
Tidal Volume and Minute Ventilation
Tidal volume is the amount of air that moves in or out of the lungs with each respiratory cycle. Minute ventilation is respiratory rate multiplied by tidal volume. Some wearable approaches, including respiratory inductance plethysmography, can estimate these volume measures once the signal has been calibrated.
Breathing Patterns and Apnea Events
Some sensors capture the timing and pattern of breathing, including pauses. Apnea events, periods where breathing stops, are relevant in several conditions. They can occur during sleep and, in some conditions, while a person is awake, so the measurement window should follow the condition rather than assume nighttime.
Cough Frequency
Cough frequency, the number of coughs over a period, can be recorded continuously, including overnight. It captures a symptom patients experience directly and can find hard to report accurately from memory.
Why Is Respiratory Rate Hard to Measure by Observation?
Respiratory rate is hard to measure by observation because it is often estimated by eye rather than counted, and a short count may not reflect breathing across a day. The same StatPearls review states that outside intensive care settings, respiratory rate is often “estimated visually rather than counted using a standardized method, resulting in poor accuracy and reproducibility.”
Spot Checks Miss Variation
A count taken during a clinic visit reflects that moment. Breathing changes with activity, posture, sleep and symptoms, and a single observation cannot show those changes.
What Continuous Recording Adds
Wearable sensors can record breathing over hours or nights, not seconds. That gives a longer record of respiratory rate in daily life. Whether a wearable estimate performs well enough for a given population and context of use still has to be shown with evidence.
Which Sensor Approaches Are Used?
Different sensor types capture respiratory information in different ways. Each has trade-offs in comfort, performance in a given population and the measures it supports. Sensor placement matters for all of them, as covered in understanding wearable sensor types and wear location.
Respiratory Inductance Plethysmography
Respiratory inductance plethysmography (RIP) uses elastic bands worn around the rib cage and abdomen. A 2016 study in the Brazilian Journal of Physical Therapy describes how RIP “detects changes in the cross-sectional area of the rib cage and abdomen using inductive belts” and notes that portable RIP systems “incorporate belts in an elasticized vest and allow measurements to be easily obtained without a mouthpiece.” That makes RIP usable outside the clinic, in daily life and overnight.
Accelerometry
Accelerometers placed on the chest or torso can pick up the small movements of breathing. The same sensor also records physical activity and posture, which helps interpret respiratory data in context. Wrist-worn accelerometry is a separate topic, covered in actigraphy in clinical trials.
Acoustic Sensors
Microphones worn on the body can record cough sounds. Algorithms then identify and count coughs. Acoustic approaches need careful handling of privacy and background noise.
Signals From Cardiac Sensors
Respiratory rate can also be estimated from cardiac signals, because breathing causes small, regular changes in heart rate, in the electrocardiogram (ECG) signal and in optical blood volume signals.
How Does RIP Estimate Respiratory Volume?
RIP estimates respiratory volume indirectly. The bands record rib cage and abdominal movement, and a calibration step converts those movements into volume. A 2021 scoping review in Sensors explains that wearable approaches “do not directly assess the volume of air inhaled and exhaled with each breath” but assess other physical variables, such as changes in chest circumference, “that can be related to the tidal volume through a calibration model.”
Why Calibration Matters
Without calibration, RIP signals show the timing and relative size of breaths but not volume in litres. The same review states that “all methodological approaches suited for wearable solutions provide an indirect measure of the tidal volume through a calibration process.” It also describes studies examining the between-day variability of calibration parameters. For a trial, that means the calibration approach, its timing and how often it is repeated belong in the measurement plan.
How Calibration Is Done
Calibration typically compares the band signals with a reference volume measurement over a set of breaths. VivoSense has published on calibrating RIP signals to derive tidal volume measures, in a 2017 article.
From Tidal Volume to Minute Ventilation
Once tidal volume is estimated breath by breath, respiratory rate comes from the same signal. Minute ventilation follows from the two. Each derived measure carries the calibration assumptions behind it, so evidence for the calibrated measure must come from the trial’s population and conditions.
Nighttime vs Daytime Measurement
Respiratory measures often behave differently at night. Sleep reduces the variation that talking and walking add during the day, which can make some measures easier to interpret. Nighttime is also when events such as nocturnal cough and apnea events during sleep can be recorded.
Daytime measurement adds context about how breathing relates to activity, and in some conditions breathing irregularities and apnea events occur while awake. The right window depends on the concept of interest and the condition.
What Should Trial Teams Know About Cough Monitoring?
Cough monitoring counts coughs over hours or days, typically from body-worn acoustic recordings. It provides a cough-frequency count that patient reports alone do not.
Cough Counts and Patient Reports Measure Different Things
A 2022 review in the Journal of Thoracic Disease notes that subjective patient-reported outcomes (PROs) correlate moderately with cough counting. That is one reason a study may consider cough counts alongside PROs rather than as a replacement for them.
Practical Limits
The same review states that “the application of cough counters has been limited in clinical practice by the high cost and reliance on aural validation.” Aural validation means a person listens to recordings to confirm what an algorithm counted.
Planning Questions
A cough monitoring plan needs to define the recording duration, whether daytime and nighttime cough are reported separately, how recordings that capture speech are protected, and how the algorithm performs in the trial’s population.
Artifact, Movement and Context of Use
Movement Artifact
Movement can distort respiratory signals, particularly during activity. Algorithms need rules to identify and handle periods when the signal is unreliable.
Fit and Placement
Band tension, sensor position and garment fit affect signal quality. Consistent placement across wear days matters.
Population Differences
Breathing patterns in a respiratory or neurological condition can differ substantially from those in healthy adults. Validation should always be evaluated within the intended context of use. A wearable sensor validated for healthy adults may not perform similarly in patients with neurological disorders, respiratory disease, or mobility limitations. That principle runs through how to select wearable sensors for a clinical trial.
Participant Burden
Chest bands and garments can be less comfortable than a wrist device. Wear schedules need to reflect what participants can sustain, especially over long studies or overnight. Wear time and valid days in wearable clinical trials set how much wear a study needs and how to count usable days.
Published Example: Cystic Fibrosis
In a global cystic fibrosis study described in an April 2025 case study, VivoSense deployed sensor-based digital health technologies to monitor physical activity, sleep and cough across 200 devices at 18 sites worldwide. The study reported “99% data availability” and “94% wear compliance.” Those figures describe the study as a whole, not cough-counting performance. Read the cystic fibrosis case study.
How Do You Plan a Respiratory Digital Measure?
Planning a respiratory digital measure follows five stages, in order, starting from the clinical concept rather than the sensor.
- Identify a Meaningful Clinical Concept: decide which aspect of breathing or cough matters to patients in this condition.
- Select Appropriate Technologies: choose sensors suited to the measure, the wear window and the population.
- Develop Digital Biomarkers: define how respiratory rate, volume estimates, events or cough counts will be derived, including calibration and how artifact is handled.
- Establish Validation Evidence: plan analytical and clinical evidence for the population and context of use. The framework is set out in validation evidence for digital measures.
- Build Digital Endpoints: set out the analysis and the measure’s role in the trial.
Common Mistakes
Choosing a Sensor Before Defining the Measure
A device suited to respiratory rate may not suit cough counting or volume estimates, and the reverse.
Assuming Healthy-Adult Performance Applies to Patients
Respiratory and neurological conditions can change breathing patterns that algorithms rely on.
Treating Uncalibrated Signals as Volume
RIP signals without calibration show breathing patterns, not liters. Volume measures need a defined calibration approach.
Underestimating Wear Burden Overnight
Uncomfortable sensors at night can lead to removal and missing data.
Ignoring Movement Artifact
Without clear artifact rules, daytime respiratory data can be hard to interpret.
Digital Measures With VivoSense
VivoSense is a wearable sensor contract research organization (CRO) that works alongside the sponsor’s trial team and CRO on the digital measurement workstream. It helps choose the right device based on the disease state and the population of the patients, chooses what measures to capture, ships devices and trains sites, monitors real-time wear compliance, and cleans and analyzes the data into formatted regulatory-ready data packages for the study team.
VivoSense was founded in 2010.
Frequently Asked Questions
What is a normal respiratory rate for adults?
A normal resting adult respiratory rate is 12 to 20 breaths per minute.
Can wearable sensors measure respiratory rate?
Yes. Respiratory rate can be estimated from sensors such as chest bands, torso-worn accelerometers, and cardiac sensors, depending on the setting and population.
What is respiratory inductance plethysmography?
A method that uses elastic bands around the rib cage and abdomen to record breathing from changes as the body expands and contracts. The bands can be built into wearable garments.
Can RIP measure tidal volume?
RIP can estimate tidal volume once its signals are calibrated against a reference volume measurement. Minute ventilation can then be derived from tidal volume and respiratory rate.
How is cough frequency measured in clinical trials?
Usually with body-worn acoustic sensors that record cough sounds, combined with algorithms that identify and count coughs over time, often with human review of recordings.
Why measure breathing at night?
Some respiratory events, such as nocturnal cough and apnea events during sleep, occur at night, and sleep reduces some sources of signal variation. Apnea events can also occur while awake in some conditions.
What affects the quality of wearable respiratory data?
Movement artifact, sensor fit and placement, calibration for volume measures, differences between patient populations, and how consistently participants wear the device.
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