Autonomic and vascular responses to reduced limb perfusion

• Published in: Journal of applied physiology (1985) Vol. 95; no. 4; pp. 1493 - 1498
• Main Authors: Daley, Joseph C., III, Khan, Mazhar H, Hogeman, Cynthia S, Sinoway, Lawrence I
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01-10-2003; American Physiological Society
• Subjects: Adult; Biological and medical sciences; Blood Flow Velocity; Blood Pressure; Brachial Artery - physiopathology; Female; Forearm - blood supply; Forearm - innervation; Fundamental and applied biological sciences. Psychology; Heart Rate; Humans; Hydrogen-Ion Concentration; Ischemia - blood; Ischemia - physiopathology; Lactic Acid - blood; Male; Muscular system; Nervous system; Reference Values; Regional Blood Flow; Sympathetic Nervous System - physiopathology; Nervous system diseases; Cardiovascular disease; Striated muscle; Sympathetic nervous system; Blood flow; Vascular disease; Vertebrata; Mammalia; muscle blood flow; Ischemia; Autonomic nervous system; Perfusion; Hemodynamics
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00344.2002

Divisions of 1 Pulmonary, Allergy, and Critical Care and 2 Cardiology, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, Hershey 17033; and 3 Lebanon Veterans Affairs Medical Center, Lebanon, Pennsylvania 17042
Submitted 17 April 2002
; accepted in final form 23 June 2003
The purpose of this study was to examine hemodynamic responses to graded muscle reflex engagement in human subjects. We studied seven healthy human volunteers [24 ± 2 (SE) yr old; 4 men, 3 women] performing rhythmic handgrip exercise [40% maximal voluntary contraction (MVC)] during ambient and positive pressure exercise (+10 to +50 mmHg in 10-mmHg increments every minute). Muscle sympathetic nerve activity (MSNA), mean arterial blood pressure (MAP), and mean blood velocity were recorded. Plasma lactate, hydrogen ion concentration, and oxyhemoglobin saturation were measured from venous blood. Ischemic exercise resulted in a greater rise in both MSNA and MAP vs. nonischemic exercise. These heightened autonomic responses were noted at +40 and +50 mmHg. Each level of positive pressure was associated with an immediate fall in flow velocity and forearm perfusion pressure. However, during each minute, perfusion pressure increased progressively. For positive pressure of +10 to +40 mmHg, this was associated with restoration of flow velocity. However, at +50 mmHg, flow was not restored. This inability to restore flow was seen at a time when the muscle reflex was clearly engaged (increased MSNA). We believe that these findings are consistent with the hypothesis that before the muscle reflex is clearly engaged, flow to muscle is enhanced by a process that raises perfusion pressure. Once the muscle reflex is clearly engaged and MSNA is augmented, flow to muscle is no longer restored by a similar rise in perfusion pressure, suggesting that active vasoconstriction within muscle is occurring at +50 mmHg.
muscle blood flow; sympathetic nervous system; ischemia
Address for reprint requests and other correspondence: L. I. Sinoway, Div. of Cardiology, MC H047, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, P.O. Box 850, Hershey, PA 17033 (E-mail: lsinoway{at}psu.edu ).