Abstract
To assess the effect of mean skin temperature (Tsk) on active cutaneous vasodilator system, we measured skin sympathetic nerve activity (SSNA) from the peroneal nerve by microneurography during mild heat stress in 6 subjects. Skin blood flow (SkBF; laser-Doppler flowmetry) was investigated at the bretylium treated and untreated sites on the dorsal foot while monitoring sweat rate (hygrometer) at the pilocarpine treated site and mean arterial pressure (MAP; Finapres) from the middle digit. Subjects kept semi-recumbent position and wore a thermal suit perfused with warm water at 34°C, raised to 36, 38, and 40°C every 30 min. All data were collected for the last 10 min of each stage. Tsk increased from 34.8 ± 0.2°C at 34°C to 35.7 ± 0.2°C at 40°C (P<0.05) by 0.2 - 0.3°C every stage, without a change in esophageal or foot skin temperature during the first 3 stages. Cutaneous vascular conductance (CVC; SkBF/MAP) at bretylium treated site increased by 48 ± 22% at 38°C and 70 ± 23% at 40°C compared to 34°C (P<0.05). The number of sweat expulsions during 10 min increased from 30 ± 1 at 34°C to 41 ± 4 at 38°C (P<0.05) and 49 ± 6 at 40°C (P<0.05). Burst rate of SSNA increased from 11 ± 2 bursts/min at 34°C to 17 ± 3 bursts/min at 40°C (P<0.05). The amplitude of SSNA burst increased at 38 and 40°C (P<0.05) while reducing duration (P<0.05). Thus, the change in the burst pattern of SSNA at 38 and 40°C suggested the involvement of active vasodilator and/or sudomotor activity which were modulated by the rise in Tsk. [Jpn J Physiol 54 Suppl:S240 (2004)]
