Post Junctional Sudomotor and Cutaneous Vascular Responses in Noninjured Skin Following Heat Acclimation in Burn Survivors

Abstract

Thermal tolerance is improved in burn survivors following 7 days of exercise heat acclimation. It is unknown whether post-junctional sudomotor and/or cutaneous vascular adaptations in non-injured skin contribute to this improvement. Thirty-three burn survivors were stratified into moderately (17-40% BSA grafted, n = 19) and highly (>40% BSA grafted, n = 14) skin grafted groups. Nine non-burned subjects served as controls. All subjects underwent a 7 day heat acclimation protocol, which improved thermal tolerance in all groups. Before and after this heat acclimation protocol, post-junctional cutaneous vascular responses were assessed by administering increasing doses of sodium nitroprusside (SNP) and methacholine (MCh) using intradermal microdialysis in non-injured skin. MCh infusion was also used to assess post-junctional responses in sudomotor function in non-injured skin. Cutaneous vascular responses to SNP and MCh were not different between pre and post heat acclimation in either group of burn survivors (both P > 0.05). The maximal sweating rate to MCh increased post acclimation in the control group (0.41±0.20 to 0.54±0.21 mg.min−1.cm−1; P = 0.016) but was unchanged in both groups of burn survivors (both P > 0.05). The number of sweat glands activated during the highest dose of MCh was elevated in the >40% BSA grafted group (49±16 to 56±18 glands.cm2; P = 0.005) but was unchanged in control subjects and the <40% BSA grafted group (both P > 0.05). Given that post-junctional administration of MCh and SNP did not alter sweating or skin blood flow from non-injured skin of burn survivors, improved thermal tolerance in these individuals following heat acclimation is more likely a result of either an increased sweating efficiency and/or an increased neural drive for sweating.

Improved neural control of body temperature following heat acclimation in humans

“…2009a,b; Lorenzo & Minson, 2010; Pearson et al . 2017) and primates (Sato et al . 1990), only two studies have provided indirect evidence of central thermoregulatory adaptations following heat acclimation.…”

“…Nonetheless, these initial findings served as the basis for future studies attempting to more directly delineate peripheral vs. central thermoregulatory adaptations following heat acclimation. Although direct evidence for peripheral modifications of the thermoeffector organs have been demonstrated in humans (Inoue et al 1999;Buono et al 2009a,b;Lorenzo & Minson, 2010;Pearson et al 2017) and primates (Sato et al 1990), only two studies have provided indirect evidence of central thermoregulatory adaptations following heat acclimation. These studies reported a greater sweat gland expulsion frequency, a proposed marker of central sudomotor activity, following heat acclimation (Ogawa & Sugenoya, 1993) and seasonal acclimatization (Taniguchi et al 2011).…”

“…2009a,b; Lorenzo & Minson, 2010; Pearson et al . 2017) and cutaneous microvasculature (Lorenzo & Minson, 2010) in humans, as well as morphological changes to the eccrine sweat glands in primates (Sato et al . 1990).…”

“…Nadel et al (1974) first suggested that central thermoregulatory adaptations mediate the greater sweat rate observed following heat acclimation, based on the observation that heat acclimation lowered the onset threshold of the response without affecting the thermosensitivity. Nonetheless, subsequent studies provided more direct evidence that heat acclimation results in peripheral modifications of the thermoeffector organs, such as improved post-junctional cholinergic sensitivity of the sweat glands (Inoue et al 1999;Buono et al 2009a,b;Lorenzo & Minson, 2010;Pearson et al 2017) and cutaneous microvasculature (Lorenzo & Minson, 2010) in humans, as well as morphological changes to the eccrine sweat glands in primates (Sato et al 1990). By contrast, potential adaptations in the neural control of body temperature have long been hypothesized (Armstrong & Stoppani, 2002), yet no direct evidence exists to support this possibility in humans.…”

β‐Adrenergic blockade does not impair the skin blood flow sensitivity to local heating in burned and nonburned skin under neutral and hot environments in children

“…While others have furthered the understanding of temperature regulation in burned adults during passive heating [12,13,18,26,54,57,58] and exercise heat stress [21,22,43,53,54], none have studied heat exchange at rest in burned children and only a few (work from our laboratory, [33,34]) have investigated exercise heat stress in burned children. To our knowledge, this is the first study characterizing skin blood flow responses to local heating in burned and non-burned children.…”