Arterial-cardiac baroreflex function: insights from repeated squat-stand maneuvers

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 297; no. 1; pp. R116 - R123
• Main Authors: Zhang, Rong, Claassen, Jurgen A. H. R, Shibata, Shigeki, Kilic, Sinem, Martin-Cook, Kristin, Diaz-Arrastia, Ramon, Levine, Benjamin D
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.07.2009
• Subjects: Adult; Age Factors; Aged; Aging - physiology; Baroreflex; Blood Pressure; Capnography; Cardiovascular system; Cardiovascular System - innervation; Electrocardiography; Exercise; Female; Heart Rate; Homeostasis; Humans; Male; Middle Aged; Muscle Contraction; Muscle, Skeletal - innervation; Older people; Physiology; Plethysmography; Posture; Sphygmomanometers; Time Factors; Veins & arteries; Young Adult
• ISSN: 0363-6119; 1522-1490; 1522-1490
• DOI: 10.1152/ajpregu.90977.2008

1 Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas and University of Texas Southwestern Medical Center, Dallas, Texas; 2 Department of Geriatric Medicine, Radboud University Nijmegen Medical Center, The Netherlands; and 3 Department of Neurology and the Alzheimer's Disease Center, University of Texas Southwestern Medical Center, Dallas, Texas Submitted 3 December 2008 ; accepted in final form 29 April 2009 To assess baroreflex function under closed-loop conditions, a new approach was used to generate large and physiological perturbations in arterial pressure. Blood pressure (BP) and R-R interval were recorded continuously in 20 healthy young (33 ± 8 yr) and eight elderly subjects (66 ± 6 yr). Repeated squat-stand maneuvers at the frequencies of 0.05 and 0.1 Hz were performed to produce periodic oscillations in BP to provoke the baroreflex. To assess the effects of the muscle reflex and/or central command on the baroreflex, passive squat-stand maneuvers were conducted using a pulley system to assist changes in body position. Transfer function between changes in BP and R-R interval was estimated to assess the arterial-cardiac baroreflex. Relative to resting conditions, large and coherent oscillations in BP and R-R interval were produced during both active and passive squat-stand maneuvers. However, changes in BP were smaller during passive than during active maneuvers. Changes in R-R interval were reduced commensurately. Therefore, transfer function gain did not change between the two maneuvers. Compared with the young, transfer function gain was reduced and the phase became more negative in the elderly, demonstrating the well-known effects of aging on reducing baroreflex sensitivity. Collectively, these findings suggest that the changes in R-R interval elicited by BP perturbations during squat-stand maneuvers are mediated primarily by a baroreflex mechanism. Furthermore, baroreflex function can be assessed using the transfer function method during large perturbations in arterial pressure. blood pressure; heart rate; spectral analysis Address for reprint requests and other correspondence: R. Zhang, Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, 7232 Greenville Ave., Dallas, TX 75231 (e-mail: rongzhang{at}texashealth.org )