The usefulness of a laser Doppler in the measurement of the blood pressures

Objective: The purpose of this study was to evaluate the clinical value and reproducibility of laser Doppler (LD) versus photoplethysmography (PPG) in the measurement of the systolic toe blood pressure. Methods: Toe blood pressure was measured in 60 patients in different stages of peripheral vascular disease with simultaneous digital sampling of PPG and two LD signals, each with a different filter setting (3 second [LD3] and 0.03 second [LD0.03]), and cuff pressure. These measurements were repeated after 1 week. The signals were analyzed with previous results ignored. The agreement of the PPG and LD pressures and reproducibility after 1 week were assessed by calculating the intraclass correlation coefficient (ICG). The agreement variation across the range of pressure values was visually explored by means of difference plots. Results: In 19 legs with a very low pressure only LD could adequately measure the pressure, whereas PPG did not. The ICCs between PPG and LD3 and LD0.03 were 0.95 or more. The ICCs of the 1-week reproducibility of the PPG, LD3, and LD0.03 pressures were 0.92, 0.88, and 0.86, respectively. The variation was equally distributed across the range of pressures in all three methods. Conclusion: LD is a reliable alternative to PPG to measure toe blood pressures. Furthermore, LD is able to measure low pressures, which is relevant in the assessment of the presence of critical ischemia.