Whole body heat stress attenuates baroreflex control of muscle sympathetic nerve activity during postexercise muscle ischemia

• Published in: Journal of applied physiology (1985) Vol. 106; no. 4; pp. 1125 - 1131
• Main Authors: Cui, Jian, Shibasaki, Manabu, Davis, Scott L, Low, David A, Keller, David M, Crandall, Craig G
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.04.2009; American Physiological Society
• Subjects: Adult; Baroreflex - physiology; Biological and medical sciences; Blood Pressure - drug effects; Body temperature; Body Temperature - physiology; Exercise; Exercise - physiology; Female; Fundamental and applied biological sciences. Psychology; Hand Strength; Heart Rate - physiology; Heat Stress Disorders - physiopathology; Humans; Ischemia - physiopathology; Male; Metabolism; Muscle, Skeletal - blood supply; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Muscular system; Nervous system; Nitroprusside - pharmacology; Phenylephrine - pharmacology; Regional Blood Flow; Skin - blood supply; Sweating - physiology; Sympathetic Nervous System - physiology; Vasoconstrictor Agents - pharmacology; Vasodilator Agents - pharmacology; Sympathetic nerve; Temperature; Environmental factor; Cardiovascular disease; Striated muscle; Sympathetic nervous system; Stress; Vertebrata; Heat; Mammalia; Ischemia; Autonomic nervous system; Baroreflex; muscle metaboreceptors
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00135.2008

1 Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, Texas; 2 Penn State Heart and Vascular Institute, Penn State College of Medicine, Hershey, Pennsylvania; and 3 University of Texas Southwestern Medical Center, Dallas, Texas Submitted 5 February 2008 ; accepted in final form 5 February 2009 Both whole body heat stress and stimulation of muscle metabolic receptors activate muscle sympathetic nerve activity (MSNA) through nonbaroreflex pathways. In addition to stimulating muscle metaboreceptors, exercise has the potential to increase internal temperature. Although we and others report that passive whole body heating does not alter the gain of the arterial baroreflex, it is unknown whether increased body temperature, often accompanying exercise, affects baroreflex function when muscle metaboreceptors are stimulated. This project tested the hypothesis that whole body heating alters the gain of baroreflex control of muscle sympathetic nerve activity (MSNA) and heart rate during muscle metaboreceptor stimulation engaged via postexercise muscle ischemia (PEMI). MSNA, blood pressure (BP, Finometer), and heart rate were recorded from 11 healthy volunteers. The volunteers performed isometric handgrip exercise until fatigue, followed by 2.5 min of PEMI. During PEMI, BP was acutely reduced and then raised pharmacologically using the modified Oxford technique. This protocol was repeated two to three times when volunteers were normothermic, and again during heat stress (increase core temperature 0.7°C) conditions. The slope of the relationship between MSNA and BP during PEMI was less negative (i.e., decreased baroreflex gain) during whole body heating when compared with the normothermic condition (–4.34 ± 0.40 to –3.57 ± 0.31 units·beat –1 ·mmHg –1 , respectively; P = 0.015). The gain of baroreflex control of heart rate during PEMI was also decreased during whole body heating ( P < 0.001). These findings indicate that whole body heat stress reduces baroreflex control of MSNA and heart rate during muscle metaboreceptor stimulation. sympathetic nervous system; muscle metaboreceptors Address for reprint requests and other correspondence: C. G. Crandall, Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, 7232 Greenville Ave., Dallas, TX 75231 (e-mail: CraigCrandall{at}texashealth.org )