The oscillometric waveform: why you should read the curve before trusting the blood pressure number

In electrocardiography, in pulse oximetry (SpO2) and in capnography (ETCO2), veterinarians have learned to read the wave before trusting the number: a clean tracing validates the heart rate, a regular plethysmographic curve validates the saturation, and a well-formed capnographic ramp validates the ETCO2. Blood pressure measurement should be no different. Oscillometry does not measure pressure directly: it derives it from the curve of amplitudes of the oscillations that the arterial pulse imprints on the cuff. The quality of that curve, in practice, determines how reliable the displayed systolic (SAP), diastolic (DAP) and mean (MAP) pressures actually are.

How oscillometry actually measures pressure

In the oscillometric method, the device inflates the cuff above systolic pressure and deflates it in a controlled way, recording at each step the small pressure oscillations that the arterial pulse produces inside the cuff. The amplitude of these oscillations is not constant: it rises, reaches a maximum and then falls as cuff pressure decreases. The set of these amplitudes, point by point, forms an envelope, which is the oscillometric waveform.

From that envelope the algorithm estimates the three pressures. The peak amplitude of the envelope corresponds to mean arterial pressure (MAP), while systolic and diastolic pressures are estimated at points of the envelope defined by characteristic amplitude ratios that are specific to each algorithm. In other words, the number on the screen is a reading of the curve, not a direct measurement of the artery. Without the curve, the operator sees only the end result of a calculation whose input cannot be inspected.

Why the shape of the curve matters for accuracy

If pressure is derived from the envelope, then the shape of that envelope governs accuracy. Because the number is born from amplitude ratios applied to the curve, any distortion of the envelope, from motion artifact, muscle tremor or irregular beats, shifts the calculated pressures. In veterinary practice this has a direct echo: agreement between non-invasive methods varies with technique and cuff position (Garofalo et al., 2012) and, even in apparently healthy dogs, there are large intra-individual differences between successive readings, with situational hypertension common in the consultation (Marynissen et al., 2023). The quality of each reading, therefore, matters as much as the displayed value.

The clinical consequence is direct: motion artifact, muscle tremor or the irregular beats of an arrhythmia distort the envelope and, with it, the calculated pressures, without necessarily triggering any alert on the device. A number displayed with a plausible appearance may in fact conceal a poor curve. This is why seeing the curve is what lets the operator distinguish a reliable reading from a measurement that should be discarded and repeated.

The limit of conventional oscillometry

Conventional oscillometry hands the user only the result: a number for SAP, DAP and MAP, and nothing of the signal that produced it. Internally the device built and analyzed the envelope, but the operator has no access to it. In practice this means there is no way to audit the quality of the reading: the veterinarian cannot verify whether the oscillations were regular, whether there was motion artifact, whether an arrhythmia distorted the envelope or whether the amplitude peak was well defined.

It is like trusting a heart rate without seeing the ECG tracing, or an SpO2 without looking at the plethysmographic curve. The number may be right, but it may also be wrong for a reason that stayed invisible. In cautious medicine, especially when the reading can lead to a diagnosis of hypertension and the start of therapy, relying on a value that cannot be checked is a weakness of the method, not of the patient.

What high-definition oscillometry adds

High-definition oscillometry (HDO) captures and displays the oscillometric waveform at high resolution, giving the operator exactly what conventional oscillometry lacks: the ability to assess the signal behind the number. With the curve in view, the veterinarian can recognize a clean, well-defined envelope, identify motion artifact and notice the irregularity typical of an arrhythmia, then decide on solid grounds whether to accept or repeat the reading, instead of trusting the display blindly.

In veterinary studies, HDO devices have performed well on agreement. In anesthetized dogs, compared with invasive pressure, HDO met most of the ACVIM consensus accuracy criteria for MAP and DAP, while Doppler overestimated and failed those criteria (Seliskar et al., 2012). Oscillometric methods, HDO included, also have the advantage of providing SAP, DAP and MAP, whereas Doppler generally provides reliably only systolic pressure (Knies et al., 2024; Garofalo et al., 2012). It is no coincidence that veterinary HDO has been adopted as a clinical reference method in comparisons, including to show that human wrist monitors do not replace it (Martinelli et al., 2022; Marriott, 2026).

A cautious caveat is in order: no non-invasive method perfectly reproduces intra-arterial pressure, and performance depends on a validated device and correct protocol. The gain from HDO is not to make the measurement infallible, but to make its quality verifiable.

Why this weighs so heavily in veterinary practice

Blood pressure measurement in dogs and cats is particularly vulnerable to precisely the factors that distort the curve: small patients, movement, tremor, arrhythmias and the stress of the clinical setting, the so-called white-coat effect. In apparently healthy elderly dogs, different methods can agree well on a population average and still show large intra-individual differences between readings, with situational hypertension common in the clinic (Marynissen et al., 2023). In other words, a single reading, without quality control, says little.

This is why the 2018 ACVIM consensus ties reliability to the method, not just to the number: use a validated device, a cuff width of 30 to 40 percent of the limb circumference, a calm environment, an acclimated animal, and a protocol of 5 to 7 measurements, discarding the first and aiming for a low coefficient of variation among the rest. The same consensus classifies hypertension only from SAP of 160 mmHg upward, with stratification of target-organ-damage risk above that (Acierno et al., 2018). Being able to see and assess the curve directly helps meet that rigor, because it lets you identify and discard the poor readings that would inflate the coefficient of variation and contaminate the average.

None of this replaces clinical judgment. The decision to diagnose hypertension, investigate causes and start therapy belongs to the veterinarian, who integrates the pressure with the history, the physical exam and the rest of the workup. The curve is a tool for data quality, not a diagnosis.

Conclusión: seeing the curve is the check the number alone cannot give

Just as the veterinarian does not trust a heart rate without the tracing or a saturation without the plethysmogram, it makes sense not to trust a blood pressure without being able to look at the curve it was derived from. Being able to see the oscillometric waveform is a quality check that the isolated number simply does not offer: it is what separates an auditable reading from a blind value.

This is where high definition becomes practice. The BPScan and the BPScan S use high-definition oscillometry and show the oscillometric waveform in real time, so the veterinarian can judge the quality of each reading before deciding, instead of accepting a number without context. Integrated with the INpulse One platform and the history in INcloud, these pressure data gain follow-up over time, always under the interpretation of the attending veterinarian.