title: Baroreceptor unloading does not limit forearm sweat rate during severe passive heat stress.
abstract: This study tested the hypothesis that sweat rate during passive heat stress is limited by baroreceptor unloading associated with heat stress. Two protocols were performed in which healthy subjects underwent passive heat stress that elicited an increase in intestinal temperature of ∼1.8°C. Upon attaining this level of hyperthermia, in protocol 1 (n = 10, 3 females) a bolus (19 ml/kg) of warm (∼38°C) isotonic saline was rapidly (5-10 min) infused intravenously to elevate central venous pressure (CVP), while in protocol 2 (n = 11, 5 females) phenylephrine was infused intravenously (60-120 μg/min) to return mean arterial pressure (MAP) to normothermic levels. In protocol 1, heat stress reduced CVP from 3.9 ± 1.9 mmHg (normothermia) to -0.6 ± 1.4 mmHg (P < 0.001), while saline infusion returned CVP to normothermic levels (5.1 ± 1.7 mmHg; P > 0.999). Sweat rate was elevated by heat stress (1.21 ± 0.44 mg·cm(-2)·min(-1)) but remained unchanged during rapid saline infusion (1.26 ± 0.47 mg·cm(-2)·min(-1), P = 0.5), whereas cutaneous vascular conductance increased from 77 ± 10 to 101 ± 20% of local heating max (P = 0.029). In protocol 2, MAP was reduced with heat stress from 85 ± 7 mmHg to 76 ± 8 mmHg (P = 0.048). Although phenylephrine infusion returned MAP to normothermic levels (88 ± 7 mmHg; P > 0.999), sweat rate remained unchanged during phenylephrine infusion (1.39 ± 0.22 vs. 1.41 ± 0.24 mg·cm(-2)·min(-1); P > 0.999). These data indicate that both cardiopulmonary and arterial baroreceptor unloading do not limit increases in sweat rate during passive heat stress.
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas; Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York;
authors.forename: Zachary J
authors.initials: ZJ
authors.lastname: Schlader
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas;
authors.forename: Daniel
authors.initials: D
authors.lastname: Gagnon
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas; Department of Public Health and Clinical Medicine, Umeå University, Umeå Sweden; and.
authors.forename: Rebekah A I
authors.initials: RA
authors.lastname: Lucas
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas; Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado.
authors.forename: James
authors.initials: J
authors.lastname: Pearson
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas; CraigCrandall@texashealth.org.
authors.forename: Craig G
authors.initials: CG
authors.lastname: Crandall
mesh_terms: D000328:Adult; D062186:Arterial Pressure / Q000187:drug effects / Q000502:physiology; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology; D002496:Central Venous Pressure / Q000187:drug effects / Q000502:physiology; D005260:Female; D005334:Fever / Q000503:physiopathology; D005542:Forearm / Q000502:physiology*; D018869:Heat-Shock Response / Q000187:drug effects / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology; D011311:Pressoreceptors / Q000187:drug effects / Q000502:physiology*; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D012867:Skin / Q000187:drug effects / Q000503:physiopathology; D013312:Stress, Physiological / Q000187:drug effects / Q000502:physiology*; D013542:Sweat / Q000187:drug effects / Q000502:physiology*; D013546:Sweating / Q000187:drug effects / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology
chemical_list: D010656:Phenylephrine
keywords: arterial baroreceptors; cardiopulmonary baroreceptors; central venous pressure; hyperthermia; skin blood flow; sweat rate