Plethysmograph-Based Self-Assessment Device for Carotid-Femoral Pulse Wave Velocity Measurement: A Pilot Usability Study.

Arterial stiffness, a proxy of vascular aging is an important marker of cardiovascular events and mortality, independent of traditional risk factors. The aortic or carotid-femoral pulse wave velocity (cf-PWV) is the gold standard for determining arterial stiffness. Measuring arterial stiffness can help identify people who are at risk early on. State-of-the-art devices, majorly employing applanation tonometry at the carotid site, demand extensive skill, are costly, and are not intended for out-of-clinic use. However, a device that is suitable for homecare and primary health settings would facilitate primordial care. To address this gap, we have developed a novel easy-to-use, fully automated, and affordable photoplethysmography-based device for measuring cf-PWV. An in-vivo study on 25 subjects was conducted to investigate the device's usability by comparing self and expert-performed measurements, and by quantifying the user experience (score out of 5). A strong correlation (r = 0.88) and a statistically insignificant bias indicated the measurement reproducibility in self-versus expert-performed measurements. An average usability score of 3.98 ± 0.83 given by the participants showed the convenience and ease of use of the device. The results demonstrate the feasibility and reliability of using the device by inexperienced operators, even when newly introduced. Future clinical studies are in progress to assess the device's accuracy in comparison to gold-standard reference equipment.Clinical Relevance-This pilot study revealed the device's potential to offer a user-friendly solution for home care and other non-hospital settings.

Operator Variabilities in Carotid Pulse Wave Velocity Measured by an Image-free Ultrasound Device.

Local pulse wave velocity (PWV) has gained much attention in the last decade due to its ability to provide localized stiffness information from a target vessel and cater to several applications beyond regional PWV. Transit time-based methods are the most straightforward, but their reliability is highly dependent on the blood pulse sensing modality. Conventional ultrasound systems directly measure the blood pulse (as diameter or flow velocity); however, they offer limited frame rates resulting in poor resolution signals. Advanced systems supporting high frame rates are expensive, complex, and not amenable to field and resource-constraint settings. We have developed a high frame image-free ultrasound system to address this gap for automated and online measurement of local PWV. In an earlier in-vitro study, we have demonstrated its accuracy. In this work, we aim to investigate its in-vivo reliability. A study on 15 young, healthy subjects was conducted to assess the intra-and inter-operator repeatability of the developed system. The yielded local PWVs from the left carotid artery were within the range of 2.5 to 5.8 m/s. The device provided highly repeatable intra- and inter-operator measurements with ICC of 0.94 and 0.88, respectively. The bias for the intra- and inter-operator trials was statistically negligible (p > 0.005). The study demonstrated the potential of the high frame rate device to perform reliable measurements in-vivo. Clinical Relevance- This work aims to provide and validate an easy-to-use affordable and fully-automated high frame rate ultrasound technology for the measurement of online local PWV that is currently lacking.

Comparison of Approximated and Actual Bramwell-Hill Equation Implementation for Local Pulse Wave Velocity: Ex-vivo Study.

Bramwell-Hill (BH) equation is widely adopted for the evaluation of local pulse wave velocity (PWV), primarily for its theoretical association with the vessel's distensibility. Its implementation, however, requires arterial pressure and diameter waveforms simultaneously from a single site. Owing to the challenges associated with such a noninvasive recording, an approximated BH equation is adopted without requiring the entire pressure waveform but only the diastolic and systolic values. The approximated BH method yields a single value of local PWV as opposed to the actual method that provides instantaneous PWV within a cardiac cycle. This study aims to provide the currently lacking insights into how the approximate versus actual BH implementations compare. The study also addresses the pivotal question of which instantaneous value within the cardiac cycle corresponds to the approximated BH. An ex-vivo study was conducted for this purpose, emulating different flow conditions (changing mean and pulse pressures) to vary the local PWV within the range of 4.4 to 8.9 m/s. The results revealed the expected (pressure-dependent) incremental nature of local PWV due to hyper-elastic behavior of the artery, with systolic BH-PWV > diastolic BH-PWV by 13.6%. The approximate BH-PWV was similar to actual BH-PWV obtained from mean pressure level. It further underestimated the systolic, and overestimated the diastolic PWVs by 8.5% and 6.6%, respectively. Clinical Relevance - When estimated BH-PWV estimates are compared to normal values for patient classification or utilized as a reference standard in validation studies these findings become extremely important.