TY - JOUR
T1 - Blood pressure regulation during cardiac autonomic blockade
T2 - Effect of fitness
AU - Smith, M. L.
AU - Hudson, D. L.
AU - Graitzer, H. M.
AU - Raven, P. B.
PY - 1988
Y1 - 1988
N2 - The purpose of this study was to determine the role of the autonomic nervous system's control of the heart in fitness-related differences in blood pressure regulation. The cardiovascular responses to progressive lower-body negative pressure (LBNP) were studied during unblocked (control) and full blockade (experimental) conditions in 10 endurance-trained (T) and 10 untrained (UT) men, aged 20-31 yr. The experimental conditions included β1-adrenergic blockade (metoprolol tartrate), parasympathetic blockade (atropine sulfate), or complete blockade (metoprolol and atropine). Heart rate, blood pressure, forearm blood flow, and cardiac output were measured at rest and -16 and -40 Torr LBNP. Forearm vascular resistance, peripheral vascular resistance, and stroke volume were calculated from these measurements at each stage of LBNP. Blood pressure was maintained, primarily by augmented vasoconstriction, equally in T and UT subjects during complete and atropine blockade. The fall in systolic and mean pressure from 0 to -40 Torr was greater (P < 0.05) in the T subjects during the unblocked and metoprolol blockade conditions. This reduced blood pressure control during unblocked condition was attributable to attenuated vasoconstrictor and chronotropic responses in the T subjects. We hypothesize that an autonomic imbalance (elevated base-line parasympathetic activity) in highly trained subjects restricts reflex cardiac responses, which accompanied by an attenuated vasoconstrictor response, results in attenuated blood pressure control during a steady-state hypotensive stress.
AB - The purpose of this study was to determine the role of the autonomic nervous system's control of the heart in fitness-related differences in blood pressure regulation. The cardiovascular responses to progressive lower-body negative pressure (LBNP) were studied during unblocked (control) and full blockade (experimental) conditions in 10 endurance-trained (T) and 10 untrained (UT) men, aged 20-31 yr. The experimental conditions included β1-adrenergic blockade (metoprolol tartrate), parasympathetic blockade (atropine sulfate), or complete blockade (metoprolol and atropine). Heart rate, blood pressure, forearm blood flow, and cardiac output were measured at rest and -16 and -40 Torr LBNP. Forearm vascular resistance, peripheral vascular resistance, and stroke volume were calculated from these measurements at each stage of LBNP. Blood pressure was maintained, primarily by augmented vasoconstriction, equally in T and UT subjects during complete and atropine blockade. The fall in systolic and mean pressure from 0 to -40 Torr was greater (P < 0.05) in the T subjects during the unblocked and metoprolol blockade conditions. This reduced blood pressure control during unblocked condition was attributable to attenuated vasoconstrictor and chronotropic responses in the T subjects. We hypothesize that an autonomic imbalance (elevated base-line parasympathetic activity) in highly trained subjects restricts reflex cardiac responses, which accompanied by an attenuated vasoconstrictor response, results in attenuated blood pressure control during a steady-state hypotensive stress.
UR - http://www.scopus.com/inward/record.url?scp=0023696391&partnerID=8YFLogxK
U2 - 10.1152/jappl.1988.65.4.1789
DO - 10.1152/jappl.1988.65.4.1789
M3 - Article
C2 - 2846497
AN - SCOPUS:0023696391
SN - 8750-7587
VL - 65
SP - 1789
EP - 1795
JO - Journal of Applied Physiology
JF - Journal of Applied Physiology
IS - 4
ER -