Features of the non-contact carotid pressure waveform: Cardiac and vascular dynamics during rebreathing

Abstract

This report amplifies and extends prior descriptions of the use of laser Doppler vibrometry (LDV) as a method for assessing cardiovascular activity, on a non-contact basis. A rebreathing task (n = 35 healthy individuals) was used to elicit multiple effects associated with changes in autonomic drive as well as blood gases including hypercapnia. The LDV pulse was obtained from two sites overlying the carotid artery, separated by 40 mm. A robust pulse signal was obtained from both sites, in accord with the well-described changes in carotid diameter over the blood pressure cycle. Emphasis was placed on extracting timing measures from the LDV pulse, which could serve as surrogate measures of pulse wave velocity (PWV) and the associated arterial stiffness. For validation purposes, a standard measure of pulse transit time (PTT) to the radial artery was obtained using a tonometric sensor. Two key measures of timing were extracted from the LDV pulse. One involved the transit time along the 40 mm distance separating the two LDV measurement sites. A second measure involved the timing of a late feature of the LDV pulse contour, which was interpreted as reflection wave latency and thus a measure of round-trip travel time. Both LDV measures agreed with the conventional PTT measure, in disclosing increased PWV during periods of active rebreathing. These results thus provide additional evidence that measures based on the non-contact LDV technique might provide surrogate measures for those obtained using conventional, more obtrusive assessment methods that require attached sensors.

Non-contact Quantification of Jugular Venous Pulse Waveforms from Skin Displacements

“…For this reason, Casaccia et al . 21 could not directly estimate the intravenous pressure from overlying skin displacements. The difficulty of finding a direct relation between pressure waveforms and displacement waveforms may be due to the lack of understanding of the mechanical properties and thickness of the soft tissues (dermis and adipose) of the skin and vessel, which vary from patient to patient 22 .…”

Signal Diversity for Laser-Doppler Vibrometers with Raw-Signal Combination

“…A possible use case is medical applications, where LDVs are used for contactless measurements, such as monitoring cardiovascular activity [5,23]. In such cases, it is not always possible to guarantee sufficient reflectivity of the skin and that the patient does not move, or the appropriate procedures involved in ensuring this require greater effort [23]. For this application, signal diversity could decrease noise contribution of laser speckle effects, or even eliminate the need for time-consuming preparation of the skin.…”

Silicon photonics-based laser Doppler vibrometer array for carotid-femoral pulse wave velocity (PWV) measurement

“…they are easily sensed by finger palpation over superficial arteries such as the carotid and femoral), they are therefore measurable using LDV, as previously demonstrated [15,16]. LDV has previously been used for the non-contact detection of the carotid pulse, both as a means of measuring blood pressure [17] and, more generally, for deriving physiological information from its shape and timing [18]. However, medical applications of industrial LDV systems for PWV measurement have been limited by the fact that they are built on discrete optics and thus are bulky and expensive.…”