A standard pulse oximeter measures oxygen saturation and heart rate, not respiratory rate. But the light signal it uses to measure those things also carries subtle breathing-related fluctuations, and newer devices can extract a respiratory rate from that signal with surprising accuracy. Whether your particular oximeter does this depends on its software and intended use, because the hardware alone is not enough.
What a Pulse Oximeter Actually Measures
Pulse oximeters work by shining two wavelengths of light through your fingertip (or earlobe, or forehead) and measuring how much light is absorbed by the blood flowing underneath. Oxygenated and deoxygenated hemoglobin absorb these wavelengths differently, so the device can calculate your blood oxygen level. The technique behind this is called photoplethysmography, or PPG, and it detects blood volume changes in real time.1PubMed Central. Photoplethysmography for blood volumes and oxygenation changes during intermittent vascular occlusions The classic readout on a pulse oximeter is two numbers: SpO2 (your oxygen saturation) and pulse rate. Respiratory rate is not part of the original design.
That matters because many people clip on a finger oximeter expecting it to tell them how fast they are breathing. It won’t, at least not with the standard firmware most devices ship with. A conventional pulse oximeter will only flag a breathing problem indirectly, after your oxygen levels have already dropped. As one clinical review put it, pulse oximetry alone is a lagging indicator of respiratory compromise because it detects poor breathing only after hypoxia has set in.2PubMed Central. Pulse oximetry-derived respiratory rate in general care floor patients By then, the situation may already be serious.
How Breathing Hides Inside the PPG Signal
Even though a basic oximeter ignores respiratory rate, the raw PPG waveform it records is shaped by your breathing in ways that are invisible on the display but visible to software. Every time you inhale, the negative pressure in your chest changes blood flow slightly: the volume of blood in your fingertip fluctuates, the timing between heartbeats shifts, and the amplitude of each pulse wave rises and falls. These are often described as three types of respiratory “modulation” embedded in the PPG signal.
Research comparing these modulations found that frequency modulation, the subtle speeding up and slowing down of your heart rate in sync with breathing, tends to be the most reliable marker of respiratory rate. During normal breathing, it was the only modulation type whose estimated breathing rate was not statistically different from the true rate measured by a reference device.3IOPscience / PubMed Central. Comparison of different modulations of photoplethysmography in extracting respiratory rate: from a physiological perspective During deeper breathing, other modulations also became usable, but frequency modulation consistently had the smallest estimation error. The strength of these modulations varies depending on where the sensor sits: finger and forehead sensors picked up stronger signals than other body sites.
The upshot is that the raw data for respiratory rate is already present in any pulse oximeter’s signal. Whether you get a breathing rate reading depends entirely on whether the device has software designed to pull it out.
How Accurate Are Oximeter-Derived Respiratory Rates?
The strongest validation data comes from the hospital setting. A multicenter study tested Medtronic’s Nellcor respiratory rate software against capnography, a reference method that measures CO2 in exhaled breath, across both healthy volunteers and hospitalized patients. Overall, 94% of measurements fell within 3 breaths per minute of the reference rate, with a mean bias of just 0.18 breaths per minute. In controlled lab conditions with healthy volunteers, 99% of readings landed within 3 breaths per minute; in the less-controlled hospital environment, 91% did.4PubMed Central. Multicenter Study Validating Accuracy of a Continuous Respiratory Rate Measurement Derived From Pulse Oximetry: A Comparison With Capnography The correlation with the reference was strong at 0.92. For a device that adds respiratory monitoring without any extra sensors, that is a solid performance.
An earlier study in chest clinic outpatients, where breathing rates ranged widely from about 6 to 36 breaths per minute, found that a PPG-based method matched the reference rate to within 1 breath per minute for every patient.5PubMed. Measurement of respiratory rate from the photoplethysmogram in chest clinic patients That study was smaller and used a custom algorithm, but it demonstrates the potential ceiling for accuracy when conditions are favorable.
One comparison worth noting: when pitted against an acoustic monitoring device (which listens to breathing sounds through a neck sensor), the oximeter-derived rate performed better during slowing breathing and during routine patient activities like talking and moving. The acoustic device had the edge at very high breathing rates.6PubMed Central. Acoustic respiration rate and pulse oximetry-derived respiration rate: a clinical comparison study The practical takeaway is that oximeter-derived rates hold up well in exactly the scenario clinicians worry about most: a patient whose breathing is gradually slowing and who might not trigger an alarm until oxygen levels crash.
How Does It Compare to ECG-Based Breathing Estimates?
Electrocardiograms also carry respiratory modulations, because chest expansion during breathing shifts the position of the heart and subtly changes the electrical signal. A systematic comparison of algorithms found that, in general, ECG-based respiratory rate estimates performed somewhat better than PPG-based ones.7Physiological Measurement. An assessment of algorithms to estimate respiratory rate from the electrocardiogram and photoplethysmogram But the gap narrowed considerably when researchers used fusion techniques, combining multiple modulation types to improve accuracy. A separate study using ambulatory hospital patients found a mean error of 1.8 breaths per minute using fused ECG modulations and, critically, found no statistically significant difference between ECG-based, PPG-based, and combined ECG/PPG approaches.8PubMed. Derivation of respiration rate from ambulatory ECG and PPG using Ensemble Empirical Mode Decomposition: Comparison and fusion That finding suggests PPG is a valid alternative to ECG for respiratory rate in wearable sensor contexts, which is meaningful because wearing a finger or wrist sensor is far less burdensome than wearing chest electrodes.
Consumer Smartwatches and Wrist-Based Oximeters
Many modern smartwatches include PPG sensors on the wrist, and some now offer respiratory rate estimates, particularly during sleep. A validation study of a consumer smartwatch against polysomnography (the gold-standard sleep study) found a root mean squared error of about 1.6 breaths per minute for continuous overnight measurements, with a small bias of under half a breath per minute. For people with normal to moderate obstructive sleep apnea, accuracy exceeded 90%. The catch: in people with severe sleep apnea, accuracy dropped to around 76-79%.9PubMed Central. Validating a Consumer Smartwatch for Nocturnal Respiratory Rate Measurements in Sleep Monitoring
A separate prototype smartwatch designed for continuous PPG-based monitoring reported agreement within 1 breath per minute of a chest strap reference device for respiratory rate, and within 3-4 beats per minute for heart rate.10PubMed Central. Kick LL: A Smartwatch for Monitoring Respiration and Heart Rate using Photoplethysmography These results came from an experimental device, not a mass-market product, but the trend is clear: wrist-worn PPG sensors are getting close to medical-grade accuracy for breathing rate, at least under quiet conditions.
The practical limitation with wrist-based devices is motion. During the day, arm movements generate noise in the PPG signal that makes respiratory rate extraction unreliable. That is why most smartwatch respiratory rate features are restricted to sleep or rest periods. If you are sitting perfectly still, a wrist sensor can estimate your breathing rate. If you are walking around, it probably cannot.
Why Motion and Poor Circulation Cause Problems
The biggest enemy of PPG-based respiratory rate is artifact. Any movement of the sensor relative to the skin, whether from fidgeting, shivering, or just shifting in bed, injects noise into the light signal that can swamp the subtle respiratory modulations. Low perfusion states, where blood flow to the extremities is reduced due to cold, low blood pressure, or peripheral vascular disease, also degrade signal quality. A study on newer-generation pulse oximeters confirmed that faulty readings increased with more motion interference and with lower perfusion.11PubMed. The effects of motion artifact and low perfusion on the performance of a new generation of pulse oximeters in volunteers undergoing hypoxemia
Algorithms have gotten better at handling these issues. One approach combines selective windowing with noise-filtering techniques to maintain accuracy even when the signal quality drops.12PubMed Central. Photoplethysmography-Based Respiratory Rate Estimation Algorithm for Health Monitoring Applications Another uses harmonic analysis and sequential fusion across time windows to suppress errors.13Biomedical Signal Processing and Control. Respiratory rate estimation from photoplethysmogram baseline wandering by harmonic analysis and sequential fusion These methods help, but they do not eliminate the problem. A finger oximeter on a patient who is shivering after surgery, or on someone whose fingers are ice cold, will struggle to produce a trustworthy respiratory rate regardless of the software behind it.
Skin Tone and Signal Quality
Pulse oximetry has faced scrutiny over accuracy differences across skin tones, and those concerns extend to respiratory rate estimates since both depend on the same light signal. A recent study using a vascular finger phantom with tunable optical properties found statistically significant differences between skin tones, with signal degradation increasing as skin pigmentation increased.14PubMed Central. Evaluation of skin pigmentation effect on photoplethysmography signals using a vascular finger phantom with tunable optical and mechanical properties This does not mean the device stops working entirely in darker-skinned individuals, but it does mean the signal-to-noise ratio is worse, which could translate to less reliable respiratory rate readings on top of the well-documented SpO2 inaccuracies. If you are using a consumer device and have darker skin, keep in mind that the respiratory rate number may be less precise than it would be for someone with lighter skin using the same device.
Home Monitoring for Chronic Lung Disease
One of the more promising applications is home monitoring for people with chronic obstructive pulmonary disease (COPD). Respiratory rate often rises before an exacerbation becomes clinically obvious, so catching that increase early could help people seek treatment before things spiral. A feasibility study gave COPD patients a PPG-based home monitor and compared it with a reference device. The PPG monitor showed a bias of about 3 breaths per minute, with wide limits of agreement ranging from roughly −11 to +17 breaths per minute.15PubMed Central. Home monitoring of breathing rate in people with chronic obstructive pulmonary disease: observational study of feasibility, acceptability, and change after exacerbation Those numbers are notably worse than what was seen in the controlled hospital studies, reflecting the messiness of real-world home use: variable sensor placement, patient movement, and inconsistent recording conditions.
That gap between lab performance and home performance is a recurring theme. The technology works well under controlled conditions, and the accuracy degrades when you move to the noisy reality of daily life. For someone monitoring a chronic condition at home, a PPG-based respiratory rate is useful for spotting trends over time, like a gradual upward drift in overnight breathing rate across several nights. It is far less useful for making decisions based on a single reading taken while sitting on the couch.
Sleep Apnea Screening
Pulse oximeter signals have also been explored as a low-cost screening tool for obstructive sleep apnea. Rather than estimating breaths per minute, these approaches analyze the PPG waveform for patterns associated with repeated airway collapse, such as cyclical desaturations and heart rate surges. One study found a strong correlation between PPG-derived and polysomnography-derived apnea-hypopnea indices, with an area under the curve above 0.90 for detecting both mild and moderate-to-severe apnea. For moderate-to-severe cases, the method had a sensitivity of 70% and specificity of 91%.16PubMed Central. Diagnosis of obstructive sleep apnea using pulse oximeter derived photoplethysmographic signals This is a screening tool, not a diagnostic replacement for a full sleep study, but it is cheap, accessible, and can flag people who need further investigation.
Why Most Finger Oximeters Still Do Not Show Respiratory Rate
Given that the raw data is there and the algorithms work reasonably well, you might wonder why most inexpensive finger oximeters still only display SpO2 and pulse. The answer is partly regulatory and partly commercial. Displaying a respiratory rate from a pulse oximeter requires the device manufacturer to validate the algorithm against reference methods and, in many markets, obtain regulatory clearance specifically for that measurement. The cheap fingertip oximeters sold for $20-$40 online are typically cleared only for SpO2 and pulse rate. They record PPG data, but they do not run the respiratory rate software.
Medical-grade bedside monitors from companies like Medtronic and Masimo increasingly offer oximeter-derived respiratory rate as an add-on feature, and some are specifically marketed for continuous monitoring on hospital wards where patients are at risk of respiratory depression from opioids. The idea of combining SpO2 and respiratory rate in a single sensor has been recognized as a way to catch problems earlier, before oxygen levels drop, by detecting slowing or irregular breathing as it starts.2PubMed Central. Pulse oximetry-derived respiratory rate in general care floor patients
Beyond PPG: Contactless and Radar-Based Approaches
Oximeter-derived respiratory rate is one piece of a broader shift toward passive, unobtrusive breathing monitoring. Researchers have explored contactless alternatives that do not require any sensor touching the body at all, including radar-based systems that detect chest wall movement from a distance and camera-based systems that analyze subtle changes in skin color or body position.17PubMed Central. Contact and Remote Breathing Rate Monitoring Techniques: A Review These are still largely in the research phase for home use, though some are being integrated into smart home devices and bedside monitors for hospital use. The advantage of PPG-based approaches is that the sensor is already on the patient for oximetry anyway; there is no extra hardware cost, just software. That convenience factor is a strong tailwind for continued adoption.
For the consumer, the landscape looks like this: if you own a recent Apple Watch, Fitbit, or Garmin, you may already see a respiratory rate estimate in your sleep data, derived from the same PPG sensor that tracks your heart rate. If you own a basic fingertip pulse oximeter, you almost certainly do not get respiratory rate. And if you are in a hospital, whether your bedside monitor reports a PPG-derived respiratory rate depends on what system the hospital uses and whether they have enabled that feature. The technology exists and works reasonably well in quiet, controlled conditions, but it has not yet become a universal default the way SpO2 monitoring did decades ago.