title: The time-variable photoplethysmographic signal; dependence of the heart synchronous signal on wavelength and sample volume.
abstract: The photoplethysmorgraphic signal (PPG) from forearm skin and the ECG were recorded simultaneously from healthy subjects. The optical signal was derived with a fibre-optic probe which consisted of 61 fibre pairs. The peak-to-peak averaged a.c.-signal was calculated. The dependency of this signal and the signal-to-noise ratio (SNR) on the light wavelength and on sample volume was studied. The light intensities used at 560 nm were 0.015 and 0.029 mWmm-2 and at 940 nm we used 0.029, 1.37 and 2.77 mWmm-2. A theoretical model for calculation of the sample volumes was also developed. The amplitude and SNR of the a.c.-signal at 560 nm is larger than at 940 nm at the same intensity (0.029 mWmm-2). At 940 nm using 1.37 and 2.77 mWmm-2 the a.c.-signal increased with the number of fibre pairs (volume) while the SNR was little affected. At 560 nm it is suggested that the major contribution to the a.c.-signal is pulsations in the ascending arterioles and at 940 nm from pulsations in the larger vessels deeper in the tissue volume under study.
authors.affiliation: Department of Biomedical Engineering, Linköping University, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Ugnell
authors.forename: P A
authors.initials: PA
authors.lastname: Oberg
mesh_terms: D000328:Adult; D001160:Arterioles / Q000502:physiology; D004562:Electrocardiography / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data; D005260:Female; D005542:Forearm; D006321:Heart / Q000502:physiology*; D006801:Humans; D008297:Male; D017156:Photoplethysmography / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D011673:Pulsatile Flow; D012016:Reference Values; D012815:Signal Processing, Computer-Assisted; D012867:Skin / Q000098:blood supply*; D012881:Skin Temperature; D013997:Time Factors