Comparison of regional variability in multi-site photoplethysmographic pulse wave characteristics

The characteristics of the photoplethysmography (PPG) pulse signal depend upon where they are made; with pulses from the various peripheral sites showing differences in amplitude and transit time, and variation of each over time. By studying the pulses obtained simultaneously from 6 peripheral sites (right and left ears, thumbs, and toes), the bilateral and segmental characteristics should allow important information about the peripheral circulation to be extracted. A multisite photoplethysmography pulse measurement and analysis system is described which includes a MATLAB-based suite of signal processing algorithms for analysis of the waveforms on a beat-to-beat basis. Multi-site pulse waveforms were collected from 20 normal subjects whilst they performed a slow paced breathing exercise at 1 breath every 10 s for 300 s. In this study the PPG pulse waveform characteristics at the 3 segmental levels (right and left ears, thumbs, and toes) were assessed using two types of analysis: (i) pulse amplitude and its variability, and (ii) pulse transit time and its variability. The mean calibrated pulse amplitudes were (in arbitrary units); ears (0.023), thumbs (0.043), and toes (0.013), with coefficients of variability; ears and thumbs 14%, and toes 20%. A significant difference in pulse transit time of 4 ms between the right and left toes was detected. The mean overall pulse transit times were; ears (0.133 s), thumbs (0.199 s), and toes (0.302 s), with coefficients of variability; ears 2.6%, thumbs 1.9%, and toes 2.1%. In the study we utilized signal processing algorithms to calculate on a beat-to-beat basis measures of pulsatility and determine a set of normative data for our multi-site pulse system.