Thermal Loading Modalities and Cutaneous Active Vasodilation
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Date
2020-09-24
Authors
Francisco, Michael
Journal Title
Journal ISSN
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Publisher
University of Oregon
Abstract
In humans, the primary response to increasing internal temperature is increased cutaneous blood flow along with sweating. These reflexes facilitate heat dissipation to the environment by expanding the thermal gradient between the core and the periphery of the body. The known mechanisms and transducers of cutaneous active vasodilation (CAVD) have been largely characterized by supine passive whole-body heating models and applied to our understanding of exercise heat loading. The goal of this dissertation was to assess the mechanisms of CAVD in response to varying thermal loading modalities and postures. First we sought to determine if posture could alter the nitric oxide component of CAVD. Second, we sought to confirm the cholinergic co-transmitter theory of active vasodilation during whole-body passive heating and expand these findings to exercise heat loading. Lastly, we sought to identify unknown vasoactive substances associated with cholinergic nerve co-transmission. Twenty four subjects were assigned to participated in one of two study protocols.
Protocol 1 assessed neuronal and endothelial nitric oxide synthase (nNOS and eNOS) isozyme contributions to the nitric oxide component of CAVD during passive whole-body heat loading in the seated and supine positions. We found that eNOS is the primary mediator of NO during CAVD (Chapter IV). This finding conflicts with the findings of other studies, which have shown that the NO component of passive whole-body heat loading is mediated by nNOS.
Protocol 2 assessed the cholinergic co-transmitter theory of CAVD during exercise and passive whole-body heat loading. As discussed in Chapter V, we found that both thermal loading modalities result in CAVD through cholinergic nerve transmission, and that vascular transduction of active vasodilator nerve activity was similar between the two modalities.
The studies described herein provide evidence that CAVD is widely the same regardless of how thermal loading is accomplished. Despite exercise and passive whole-body heat loading having largely different hemodynamic and thermodynamic profiles, the afferent signals they share in common and those that delineate them do not appear to impact the mechanisms and transducers of CAVD as was originally thought.
This dissertation includes published and unpublished co-authored material.
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Keywords
Cholinergic nerves, Cutaneous Active Vasodilation, Microcirculation, Neurotransmitters, Skin Blood Flow, Thermoregulation