The influence of epidermal thickness on transcutaneous oxygen pressure measurements in normal persons.

Transcutaneous oxygen pressure measurements (TcPO2) were performed in ten healthy men (age 30.6 years, range 28-35) in six regions: anterolaterally 10 cm below and above the knee on both legs, 5 cm laterally to umbilicus and on the inside of the left humerus, which was subsequently biopsied for measurements of epidermal thickness from the basal lamina to the uppermost layer of stratum granulosum. Transcutaneous oxygen pressure was on average 70 mmHg (range 42-88 mmHg), and that of epidermal thickness 70 microns (range 43-120 microns). Epidermis was thinnest on the inside of the humerus (mean +/- SD) 61.3 mu +/- 11.0 and about 25% thicker (NS) in the regions above and below the knees. The relationship between TcPO2 (y) and epidermal thickness (x) could be described by the regression equation y = alpha i - 0.26x where the intercept alpha i differed between subjects, the mean value being 88 mmHg (range 77-103). The common regression coefficient of -0.26 was significantly different from zero (p less than 0.01, r2 = 0.49). Although the oxygen gradient across the total epidermis can not be estimated from skin biopsies, correction for the thickness of the living part of the skin may prove beneficial when TcPO2 measurements are used as an indicator of wound healing. The results suggests that the change of oxygen tension across the living part of epidermis is 0.26 mmHg/micron at various skin locations in different subjects.