Variability of photoplethysmography peripheral pulse measurements at the ears, thumbs and toes

Pulses radiating to the periphery after each heart beat can be detected by photoplethysmography (PPG). A multi-site PPG measurement and analysis system is described for beat-to-beat analysis of the pulse waveforms. Waveforms were collected from the right and left ear lobes, thumb pads, and toe pads of 20 normal subjects whilst they performed paced breathing. The median coefficients of variation for pulse amplitude were; ears and thumbs 11%, and toes 14%. Significant differences in pulse transit time of 4 ms (to foot of pulse), and 14 ms (to peak of pulse) between the right and left toes were detected (right lagging left, p<0.01). The median pulse transit times (to foot) were; ears (0.133s), thumbs (0.199s), and toes (0.301 s), with coefficients of variation; 2.8%, 2.2%, and 1.6%, respectively. The median pulse transit times (to peak) were; ears (0.397s), thumbs (0.435s), and toes (0.515s), with coefficients of variation; 1.4%, 2.0%, and 1.5%, respectively. The authors have utilised signal processing algorithms to calculate beat-to-beat measures of pulsatility, and determined normative data for multi-site PPG pulse assessments