title: Optical assessment of recovery of tissue blood supply after removal of externally applied pressure.
abstract: The authors use photoelectric plethysmography to determine the external occlusion pressure for blood vessels in human tissue in vivo. Three wavelengths are employed; 950 nm (infra-red), 640 nm (red) and 583 nm (yellow). Each probe is applied in turn to one finger of each subject. Pressure is applied, using a neonatal blood pressure cuff, to the finger via the probe. This pressure is increased linearly to 20 kPa (150 mmHg) over 15 s and then decreased linearly to zero over 15 s. The pressure at which perfusion returns is obtained for four repeat measurements at each wavelength. The mean (+/-standard deviation) occlusion pressures for all 13 subjects investigated are 7.1 (+/-1.9) kPa for infra-red, 6.3 (+/-1.7) kPa for red and 5.8 (+/-1.8) kPa for yellow. The pressure is 0.79 (+/-0.83) kPa lower for red compared with infra-red (P < 0.01), 0.54 (+/-0.60) kPa lower for yellow compared with red (P < 0.002) and 1.3 (+/-1.0) kPa lower for yellow compared with infra-red (P < 0.005). The reduced penetration of shorter optical wavelengths can be used to detect the lower occlusion pressures of the smaller blood vessels nearer the skin surface.
authors.affiliation: Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, UK.
authors.forename: A
authors.initials: A
authors.lastname: Murray
authors.forename: D
authors.initials: D
authors.lastname: Marjanovic
mesh_terms: D000328:Adult; D003250:Constriction; D005385:Fingers / Q000098:blood supply*; D006801:Humans; D008027:Light; D008875:Middle Aged; D010991:Plethysmography / Q000379:methods*; D011312:Pressure; D012039:Regional Blood Flow