In vivo evaluation of human calf blood pressure by using different external compression strategies

Objective. Calf blood pressure (CBP) plays an important role in various clinical applications, such as determining the appropriate cuff pressure for compression therapy and diagnosis of lower extremity vascular diseases, which necessitates the integration of built-in measurement methods within the device. This study aimed to investigate the differences in human CBP assessments resulting from the application of various in vivo external compression strategies. Approach. An experimental procedure incorporating different compression strategies, specially the low-pressure-sustained mode, the slow-inflation (SI) mode and the slow-deflation (SD) mode, was conducted to capture the dynamic responses of the photoplethysmography (PPG) signal for CBP evaluation. Nineteen subjects, including 13 males and 6 females, participated in this experimental study. Feature points related to CBP were extracted from dynamic responses of the PPG signal and subjected to statistical analysis. A lumped parameter model of the human lower extremity was developed to assist in analyzing the biomechanical factors underlying these differences. Main results. The experimental results indicated that the dynamic behaviors of the PPG signal followed clear and consistent patterns, and the CBP value derived from the PPG signal in the SI mode was significantly higher than that obtained in the SD mode. Model simulation results showed that the differences in the evaluated values of the CBP between the SI and SD modes were caused by the different collapse processes of calf arteries and veins. Significance. This study could help understand the forced collapse process of blood vessels in the calf and inspire new ideas on CBP evaluation and personalized compression therapy.