Title: RECORDINGS OF REACTIVE HYPEREMIA BY TRANSCUTANEOUS PO2 AND LASER DOPPLER TECHNIQUE
Abstract: Transcutaneous PO2 (tcPO2) at 37°C reflects tissue PO2 at the border between living and dead epidermis (50 um depth). In contrast to its conventional use at 45°C tcPO2 at 37°C is hardly affected by changes in arterial PO2 but very dependent on changes in skin blood flow. Laser Doppler velocimetry (LDV) measures the speed of moving erythrocytes in the skin to a depth of 1000 um. The aim of this work was to compare these methods for noninvasive recording of reactive hyperemia in the skin. A combined tcPO2 electrode incorporating the LDV measuring probe (PerifluxR) was constructed in Huch's laboratory, Zürich, allowing recordings from the same skin site simultaneously under identical experimental conditions. The combined sensor was placed on the volar aspect of the forearm. Exercise induced and postocclusive reactive hyperemia were recorded in healthy children and adults. Both signals detected small rhytmical variations in steady state and recorded biphasically the changes in skin blood flow during and after reactive hyperemia. The time course differed between the tcPO2 and the LDV signal, the former being delayed about 30 s for the postocclusive response. A significant correlation between the postocclusive maximal peaks measured by the two methods was found (r=0.7; p<0.01; n=20), but no correlation between corresponding recordings during steady state or exercise. Since the methods measure at different depth they convey information on blood flow changes in different vascular beds. LDV measurements include shunt blood flow in the subpapillary plexa, while tcPO2 selectively measures capillary, nutritive blood flow. The time delay between the signals is partly explained by this difference in types of flow with different time constants, and partly by the time lag for a changing oxygen gradient to reach the electrode.