Myocardial infarction and stroke are two leading causes of mortality. The primary trigger for these clinical events is destabilization of atherosclerotic plaques. Plaques can be identified based on their elastic properties, derived from stress and strain in the plaque. Strain can be measured noninvasively using ultrasound [1] and the corresponding stress can be derived from the blood pressure waveform.

In 7 healthy subjects we measured the pressure waveform in the right common carotid artery using two methods. The pressure waveform obtained by applanation tonometry was scaled directly to brachial blood pressure. The carotid artery diameter waveform obtained using ultrasound echotracking was scaled to pressure based on the diastolic and mean blood pressure continuously measured in the finger artery (Finapress^®). The resulting pressure waveforms were characterized by their systolic, diastolic and pulse pressure.

The shape of the pressure waveforms obtained by the two methods correlated well (Pearson correlation: 0.87‑0.99, p<0.05). There was a significant bias in the systolic (mean±se: 15.6±2.3 mmHg) and diastolic pressure (12.6±1.7 mmHg) between the two methods (Bland-Altman, p<0.05). The pulse pressure did not have a significant bias (3.0±1.6 mmHg).

These results suggest that the pressure waveform derived from the diameter waveform and finger blood pressure systematically underestimates mean pressure but appropriately describes pressure changes over time. Consequently ultrasound data can be used for simultaneous estimation of stress and strain in the carotid artery, which makes it possible to determine the elastic properties of plaques.