Photoplethysmographic Measurements of Pulse Wave Velocity (PWV) and Blood Pressure (BP)

Overview

Theoretically, there is a correlation between the PWV and the value of the BP, mediated by the distensibility of the segment of artery where the measurements take place. The hypothesis is therefore that the measurement of the PWV through a multisite medical device for detecting the pulse wave by photoplethysmography makes it possible to deduce the value of the BP.

The aim is to test on healthy volunteers a prototype of a non-invasive, non-CE marked medical device (VOP1k ) for the continuous monitoring of pulse wave velocity (PWV) and to study the relationship between this value and the blood pressure (BP). Indeed, the monitoring of hemodynamic parameters constitutes an essential element of the basal monitoring of patients. Among these parameters, the most used and the most routine is the measurement of BP. This measurement makes it possible in particular to detect the presence or absence of arterial hypertension (HTA), which is a major cause of premature mortality, of high prevalence within the population, involving high medical costs. Contrary to what one might think, the practice of measuring BP is not completely satisfactory, each of the techniques used having characteristics likely to lead to errors of judgment. Oscillometric and auscultatory techniques give discontinuous measurements, expose to the white coat effect when they are performed by a caregiver. Arterial occlusion by external back pressure, which is the basis of these measurement techniques, causes erroneous results and discomfort during repetitive measurements. The use of commercial semi-automatic BP monitors is fraught with validation problems. The necessary confirmation of the diagnosis of hypertension, which is based on ambulatory measurements for 24 hours using these devices, is therefore questionable. The diagnosis of the importance of arterial damage at the base of hypertension could be carried by measurements of the PWV which reflects the stiffness of the arteries. However, this diagnostic means is not currently based on a technology that can be used routinely. Means of measuring BP and arterial stiffness by invasive techniques, which are themselves subject to the risk of poor signal transmission, cannot be used outside the hospital, due to the associated risks. Non-invasive continuous measurement by the volume clamp technique, although devoid of the risks of arterial catheterization, is not available outside specialized hospital departments, and also has the disadvantage of relying on the use of external counter pressure.The technique of measurement by (photoplethysmography (PPG)), i.e. the use of an optical sensor, placed in a non-invasive way on the path of a shallow artery, makes it possible to detect the passage of the pulse wave . The combined use of several sensors located at a distance from each other on the path of the same artery, thus makes it possible to determine the velocity of the pulse wave. This technique can potentially measure over short distances, which limits the sources of error, and allows continuous measurement without discomfort. Moreover, it is compatible with low-cost integration. Indeed, acquisition technologies based on microelectronics are widely developed and mature since their massive use in smartphones. The measurement of PWV makes it possible to quantify arterial stiffness, which is a direct risk factor for morbidity and mortality associated with cardiovascular pathologies. The additional interest of this measurement, in addition to the fact of its non-invasiveness, comes from the fact that there is a correlation between the PWV and the BP, and therefore that the measurement of the PWV can make it possible to obtain a measurement of the BP. It should be noted that one aspect of the aspects of blood pressure measurement consists of being able to measure the central blood pressure, that is to say that which reigns in the aorta. However, most of the measurement techniques used routinely only measure the peripheral arterial pressure, which makes it necessary to use transfer functions to know the central pressure, or to ignore the differences in central pressure/peripheral pressure behavior. The technology proposed for the measurement makes it possible to consider overcoming this problem by placing, in one of the versions, a sensor at the carotid level, which is the arterial segment that best reflects the central pressure, unlike the humeral, femoral or radial segments.

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