title: Noncontact simultaneous dual wavelength photoplethysmography: a further step toward noncontact pulse oximetry.
abstract: We present a camera-based device capable of capturing two photoplethysmographic (PPG) signals at two different wavelengths simultaneously, in a remote noncontact manner. The system comprises a complementary metal-oxide semiconductor camera and dual wavelength array of light emitting diodes (760 and 880 nm). By alternately illuminating a region of tissue with each wavelength of light, and detecting the backscattered photons with the camera at a rate of 16 frames/wavelength s, two multiplexed PPG wave forms are simultaneously captured. This process is the basis of pulse oximetry, and we describe how, with the inclusion of a calibration procedure, this system could be used as a noncontact pulse oximeter to measure arterial oxygen saturation (S(p)O(2)) remotely. Results from an experiment on ten subjects, exhibiting normal S(p)O(2) readings, that demonstrate the instrument's ability to capture signals from a range of subjects under realistic lighting and environmental conditions are presented. We compare the signals captured by the noncontact system to a conventional PPG signal captured concurrently from a finger, and show by means of a J. Bland and D. Altman [Lancet 327, 307 (1986); Statistician 32, 307 (1983)] test, the noncontact device to be comparable to a contact device as a monitor of heart rate. We highlight some considerations that should be made when using camera-based "integrative" sampling methods and demonstrate through simulation, the suitability of the captured PPG signals for application of existing pulse oximetry calibration procedures.
authors.affiliation: Department of Electronic Engineering, National University of Ireland, Maynooth, Maynooth Co, Kildare, Ireland.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Humphreys
authors.forename: Tomas
authors.initials: T
authors.lastname: Ward
authors.forename: Charles
authors.initials: C
authors.lastname: Markham
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010092:Oximetry / Q000295:instrumentation / Q000379:methods; D017156:Photoplethysmography / Q000295:instrumentation / Q000379:methods