DIURNAL-VARIATIONS IN TOTAL FOREARM AND SKIN MICROCIRCULATORY BLOOD-FLOW IN MAN

The aim of the present study was to determine diurnal variations in to tal forearm and skin microcirculatory blood flow in healthy man. At si x time points between 08.00 and 18.00 hours was measured: blood pressu re, forearm blood flow (FBF; strain gauge plethysmography), skin therm oregulatory blood flow (LDF; laser-Doppler fluxmetry), and skin nutrit ive blood flow (CBV: Capillary Blood Cell Velocity; intravital capilla ry microscopy) in 15 healthy, fasting, and resting men. FBF increased gradually from 2.8 in the morning to 4.3 ml 100 ml min-1 in the aftern oon (p < 0.001). In contrast, LDF decreased, predominantly in the morn ing, from 18.3 at 09.00 hours to 13.1 at 12.00 hours and to 12.1 perfu sion units at 17.30 hours (p < 0.001). However, performing the same pr otocol starting in the afternoon resulted in a similar initial decreas e in LDF, suggesting an acclimatization phenomenon. Although not satis tically significant, the decrease in CBV showed a similar pattern as c ompared to LDF. Blood pressure did not change. In conclusion, forearm blood flow increased during the day, probably due to diurnal variation in muscle flow. The initial decrease we observed in skin thermoregula tory blood flow is probably not related to diurnal variation but due t o long-term acclimatization to the experimental conditions. These data suggest different regulatory mechanisms for the different vascular be ds studied. Measurements of forearm blood flow should preferably be pe rformed at the same time of day, and skin microcirculatory haemodynami c measurements should be performed after a standard period of acclimat ization.