Abstract
We examined whether skin sympathetic nerve activity (SSNA) was involved in reduced cutaneous vasodilation in hypovolemic hyperthermia. Seventeen young men were divided into normovolemia (N, n=8) and 9% hypovolemia with diuretics (L; n=9). After 5-min baseline measurement, they were warmed for 45min with a perfused suit until esophageal temperature rose by 0.4°C, while SSNA (microneurography; the peroneal nerve), skin blood flow (SkBF; laser-Doppler flowmetry; the dorsal foot), and mean arterial pressure (MAP) were recorded. Although a rising rate of cutaneous vascular conductance (CVC=SkBF/MAP) during warming was 50% lower in L than N (P<0.05), increasing rates of burst frequency and amplitude of SSNA, rectified and filtered with low pass edge of 1.6Hz, were similar between N and L. Next, to assess the relationship between SSNA firing rhythm and cardiac cycle, an incidence of original SSNA spikes was counted every 0.1s bin for 3s after every R wave of ECG. In an averaged histogram of spike incidence every 1min, the peaks appeared at the same interval as those of R and the peak interval of spike (IS) was highly correlated with that of R (IR) in N (n=399, r=0.92) and L (n=443, r=0.78) for 50 min (both, P<0.001). The standard deviation of [IR-IS] (SDR-S)in L was 36% higher than N (P<0.05). Moreover, SDR-S was inversely correlated with integrated change in CVC (r=-0.64, P<0.01). Thus, increased SDR-S may be linked with reduced cutaneous vasodilation in hypovolemic hypovolemia. [J Physiol Sci. 2008;58 Suppl:S111]
