Toe Blood Pressure Measurements in Patients Suspected of Leg Ischaemia: A New Laser Doppler Device Compared with Photoplethysmography

Abstract

Objectives. To study the usefulness of a new laser Doppler (LD) device as compared with photoplethysmography (PPG) to measure toe systolic blood pressures (TBP) in patients suspected of arterial insufficiency of the legs.Design. Prospective comparative clinical study.Materials and Methods. Seventy patients (121 legs) referred to our vascular laboratory for TBP measurements were investigated using a standard PPG and a new LD instrument, incorporating a cuff inflator and probe heater.Results. Mean toe pressures with the PPG, unheated LD, and heated LD (37 °C) were 68.1, 67.2, and 75.5 mmHg, respectively. TBP with heated LD was systematically higher than with PPG (7.7 mmHg; p<0.001). Intra-class correlations between PPG vs. unheated LD and PPG vs. heated LD were good: 0.91 and 0.93, respectively. However, a considerable variation existed between PPG and LD (95% confidence interval: 45 mmHg), which were unrelated to the value of the TBP. Kappa values of agreement between PPG and unheated and heated LD to detect critical ischaemia (TBP below 30 mmHg) were good (κ=0.77 and 0.63, respectively).Conclusions. The new LD device appears a good alternative to standard PPG measurements to assess TBP, despite a rather wide variation.