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 multi-site 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 one breath every l0s for 300s. In this study the PPG pulse waveform characteristics at the three segmental levels (right and left ears, thumbs, and toes) were assessed using two types of analysis; pulse amplitude and its variability, and 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 (right lagging left, P<0.01). 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 l.9%, and toes 2.1%. In this study we have utilised 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.
Allen J, Murray A. Comparison of regional variability in multi-site photoplethysmographic peripheral pulse wave characteristics. Advances in Medical Signal and Information Processing, Conference Publication No. 476, IEE 2000, 26-31.
Dr. John Allen, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-1370.
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