title: Thermoregulatory reflexes and cutaneous active vasodilation during heat stress in hypertensive humans.
abstract: During dynamic exercise in the heat, increases in skin blood flow are attenuated in hypertensive subjects when compared with normotensive subjects. We studied responses to passive heat stress (water-perfused suits) in eight hypertensive and eight normotensive subjects. Forearm blood flow was measured by venous-occlusion plethysmography, mean arterial pressure (MAP) was measured by Finapres, and forearm vascular conductance (FVC) was calculated. Bretylium tosylate (BT) iontophoresis was used to block active vasoconstriction in a small area of skin. Skin blood flow was indexed by laser-Doppler flowmetry at BT-treated and untreated sites, and cutaneous vascular conductance was calculated. In normothermia, FVC was lower in hypertensive than in normotensive subjects (P < 0.01). During heat stress, FVC rose to similar levels in both groups (P > 0.80); concurrent cutaneous vascular conductance increases were unaffected by BT treatment (P > 0.60). MAP was greater in hypertensive than in normotensive subjects during normothermia (P < 0.05, hypertensive vs. normotensive subjects). During hyperthermia, MAP fell in hypertensive subjects but showed no statistically significant change in normotensive subjects (P < 0.05, hypertensive vs. normotensive subjects). The internal temperature at which vasodilation began did not differ between groups (P > 0.80). FVC is reduced during normothermia in unmedicated hypertensive subjects; however, they respond to passive heat stress in a fashion no different from normotensive subjects.
authors.affiliation: Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284, USA. kelloggd@uthscsa.edu
authors.forename: D L
authors.initials: DL
authors.lastname: Kellogg
authors.forename: S R
authors.initials: SR
authors.lastname: Morris
authors.forename: S B
authors.initials: SB
authors.lastname: Rodriguez
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.forename: M
authors.initials: M
authors.lastname: Grossmann
authors.forename: G
authors.initials: G
authors.lastname: Stagni
authors.forename: A M
authors.initials: AM
authors.lastname: Shepherd
mesh_terms: D001833:Body Temperature Regulation / Q000502:physiology*; D001950:Bretylium Tosylate / Q000494:pharmacology; D015444:Exercise / Q000502:physiology; D005260:Female; D018882:Heat Stress Disorders / Q000503:physiopathology*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D017078:Laser-Doppler Flowmetry; D008297:Male; D008875:Middle Aged; D012018:Reflex / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D012867:Skin / Q000098:blood supply* / Q000503:physiopathology*; D013565:Sympatholytics / Q000494:pharmacology; D014661:Vasoconstriction / Q000502:physiology; D014664:Vasodilation / Q000502:physiology*
chemical_list: D013565:Sympatholytics; D001950:Bretylium Tosylate