Derived Non-contact Continuous Recording of Blood Pressure Pulse Waveform by Means of Vibrocardiography

Abstract

Blood Pressure (BP) is considered a significant indicator of cardiac risk. By providing information about the hemodynamic load on the heart, BP detected in a central site may have added value with respect to the more familiar peripheral arterial pressure (i.e. measured on the brachial artery). Laser Doppler Vibrometry (LDV) has been demonstrated to be a reliable non-contact technique to measure the cardiovascular signals and parameters. LDV has a high sensitivity of acquisition and it is able to measure the skin vibrations related to cardiac activity when the laser beam is pointed in correspondence of the carotid artery. The obtainable vibrational signal (i.e. a velocity signal), VibroCardioGram (VCG), can provide relevant physiological parameters, including Heart Rate (HR) as well as more advanced features encoded in the contour of the pulse waveform. In this work, the authors aim to discuss the possibility of deriving the blood pressure signal from the vibrations of the carotid artery detected by LDV. 6 healthy participants were tested; the VCG was calibrated by means of diastolic and mean arterial pressure values measured by means of an oscillometric cuff. An exponential model was applied to the VCG signal of each participant in order to derive the pressure waveform from the displacement of the investigated vessel. Results show an average difference of around 20% between systolic pressure measured at brachial level (i.e. peripheral pressure value) and systolic pressure derived from VCG signal measured over the carotid artery (i.e. central pressure). This is consistent with the literature describing the physiological increase of Systolic Blood Pressure (SBP) and Pressure Pulse (PP) at increased distances from the heart (because of the presence of reflected waves). Moreover, the average measured displacements of the carotid artery are physiologically reliable (i.e. hundreds of micrometers). LDV seems to have the potential of correctly detecting the pressure waveform without contact. However, a comparison with a reference method is required to validate the proposed measurement technique.