| Research Abstract |
In order to clarify the similarity and difference between muscle and skin sympathetic nerve activity, responses to ambient temperature change were analyzed. Previous studies have revealed that good thermoregulatory function requires common activities in muscle and skin sympathetic nerve activities since the maintenance of constant core temperature against ambient temperature change requires periodicity of both sympathetic nerve activities against the ambient temperature change as a part of feedback/feedforward mechanism. The present study examined the symmetric property of the cross-correlation between muscle and skin sympathetic nerve activities, and the symmetry of time lag was regarded as the indicator of the thermoregulatory function. Eight healthy young men/women were served as the subjects. Muscle and skin sympathetic nerve activities were simultaneously recorded from the bilateral tibial nerves by double recording technique of microneurography. The ambient temperature was change
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d from 25 to 15 or 40℃ in random order. The cross-correlogram and frequency analysis by the maximum entropy method were calculated for 20 min during cold and heat exposure. In spite of the merits of thermoregulation, cardiac, respiratory, 10 sec (Mayer) and 20 sec rhythms were apparent in their spectral peaks. Good thermoregulatory subjects showed common spectral peaks between muscle and skin sympathetic nerve activities except cardiac rhythm. In cold exposure, both muscle and skin sympathetic nerve activities were enhanced, and synchronized with Mayer (10 sec) rhythm. In heat exposure, cardiac and respiratory component in both sympathetic nerve activities were enhanced, with synchronization of Mayer rhythm. Poor thermoregulatory subjects showed a large distribution in spectral band of skin sympathetic nerve activity, and the spectral peak of skin sympathetic nerve activity was dependent on their thermoregulatory function. It is suggested that spectral peak of muscle sympathetic nerve activity synchronizing to cardiac and 20 sec rhythms is dependent on the thermoregulation as well as the heat loss, which was regulated by the vasoconstrictive function of skin sympathetic nerve activity. Less
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