Progressive muscle metaboreflex activation gradually decreases spontaneous heart rate baroreflex sensitivity during dynamic exercise

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 298; no. 2; pp. H594 - H600
• Main Authors: Sala-Mercado, Javier A, Ichinose, Masashi, Coutsos, Matthew, Li, Zhenhua, Fano, Dominic, Ichinose, Tomoko, Dawe, Elizabeth J, O'Leary, Donal S
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.02.2010
• Subjects: Animals; Autonomic Nervous System - physiology; Baroreflex - physiology; Blood pressure; Blood Pressure - physiology; Cardiac Output - physiology; Dogs; Exercise; Feedback, Physiological - physiology; Female; Heart; Heart rate; Heart Rate - physiology; Male; Models, Animal; Muscle, Skeletal - metabolism; Musculoskeletal system; Physical Conditioning, Animal - physiology; Reflex - physiology; Ventricular Function, Left - physiology
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.00908.2009

Departments of 1 Physiology and 2 Surgical Research Services and 3 Cardiovascular Research Institute, Wayne State University School of Medicine, Detroit, Michigan; 4 Human Integrative Physiology Laboratory, School of Business Administration, Meiji University, Tokyo; 5 Laboratory for Applied Human Physiology, Faculty of Human Development, Kobe University, Kobe; 6 Laboratory for Human Performance Research, Osaka International University, Osaka, Japan; and 7 Department of Cardiology, Qilu Hospital of Shandong University, Shandong, China Submitted September 24, 2009 ; accepted in final form November 25, 2009 Ischemia of active skeletal muscle elicits a pressor response termed the muscle metaboreflex. We tested the hypothesis that in normal dogs during dynamic exercise, graded muscle metaboreflex activation (MMA) would progressively attenuate spontaneous heart rate baroreflex sensitivity (SBRS). The animals were chronically instrumented to measure heart rate (HR), cardiac output (CO), mean and systolic arterial pressure (MAP and SAP), and left ventricular systolic pressures (LVSP) at rest and during mild or moderate treadmill exercise before and during progressive MMA [via graded reductions of hindlimb blood flow (HLBF)]. SBRS [slopes of the linear relationships (LRs) between HR and LVSP or SAP during spontaneous sequences of 3 consecutive beats when HR changed inversely vs. pressure] decreased during mild exercise from the resting values (–5.56 ± 0.86 vs. –2.67 ± 0.50 beats·min –1 ·mmHg –1 , P <0.05), and in addition, these LRs were shifted upward. Progressive MMA gradually and linearly increased MAP, CO, and HR; linearly decreased SBRS; and shifted LRs upward and rightward to higher HR and pressures denoting baroreflex resetting. Moderate exercise caused a substantial reduction in SBRS (–1.57 ± 0.38 beats·min –1 ·mmHg –1 , P <0.05) and both an upward and rightward resetting. Gradual MMA at this higher workload also caused significant progressive increases in MAP, CO, and HR and progressive decreases in SBRS, and the LRs were shifted to higher MAP and HR. Our results demonstrate that gradual MMA during mild and moderate dynamic exercise progressively decreases SBRS. In addition, baroreflex control of HR is progressively reset to higher blood pressure and HR in proportion to the extent of MMA. exercise reflexes; pressor response; arterial baroreflex sensitivity Address for reprint requests and other correspondence: D. S. O'Leary, Dept. of Physiology, Wayne State Univ. School of Medicine, 540 East Canfield Ave., Detroit, MI 48201 (e-mail: doleary{at}med.wayne.edu ).