Hydrostatic Pressure Compensator for Evaluation of Carotid Stiffness using A-Mode Ultrasound: Design, Characterization, and In-Vivo Validation

Abstract

Arterial stiffness measured from central arteries is widely recognized as a prognostic marker for cardiovascular risk stratification. Measurements in sitting posture make stiffness assessment potentially more rapid and feasible for large-scale population-level field screening. However, the blood pressure (BP) required for stiffness evaluation must be compensated for any hydrostatic pressure offset while performing measurements in a sitting posture. In this work, we developed and validated a hydrostatic pressure compensation unit integrated with our A-mode ultrasound device for carotid artery stiffness. The system was characterized, and its design parameters were carefully considered for concurrence with a physiologically interesting range. The smallest change it could reliably measure was 2 mm, which corresponded to 0.3 mmHg of blood pressure. The device was validated on 20 human subjects (11 males and 9 females). The results demonstrated that the average carotid systolic and diastolic pressures compensated with the hydrostatic pressure were 29% and 22% lesser than those without compensation. The ANOVA showed a statistically significant difference ($\mathrm{p} < 0.0001$) between the $\beta$ obtained from compensated ($5.21\ \pm\ 0.43$) and uncompensated ($5.73\ \pm\ 0.22$) pressures. Whereas Ep, AC did not show a statistically significant difference as they rely on the pulse pressure, which was not affected by the hydrostatic pressure correction. Conclusively, hydrostatic pressure affects the stiffness markers that rely on the absolute pressure values.