title: Rapid blunting of sympathetic vasoconstriction in the human forearm at the onset of exercise.
abstract: The purpose of this study was to test the hypothesis that sympathetic vasoconstriction is rapidly blunted at the onset of forearm exercise. Nine healthy subjects performed 5 min of moderate dynamic forearm handgrip exercise during -60 mmHg lower body negative pressure (LBNP) vs. without (control). Beat-by-beat forearm blood flow (Doppler ultrasound), arterial blood pressure (finger photoplethysmograph), and heart rate were collected. LBNP elevated resting heart rate by approximately 45%. Mean arterial blood pressure was not significantly changed (P = 0.196), but diastolic blood pressure was elevated by approximately 10% and pulse pressure was reduced by approximately 20%. At rest, there was a 30% reduction in forearm vascular conductance (FVC) during LBNP (P = 0.004). The initial rapid increase in FVC with exercise onset reached a plateau between 10 and 20 s of 126.6 +/- 4.1 ml. min(-1). 100 mmHg(-1) in control vs. only 101.6 +/- 4.1 ml. min(-1). 100 mmHg(-1) in LBNP (main effect of condition, P = 0.003). This difference was quickly abolished during the second, slower phase of adaptation in forearm vascular tone to steady state. These data are consistent with a rapid onset of functional sympatholysis, in which local substances released with the onset of muscle contractions impair sympathetic neural vasoconstrictor effectiveness.
authors.affiliation: School of Physical and Health Education and Department of Physiology, Queen's University, Kingston, Ontario K7L 3N6, UK. mt29@post.queensu.ca
authors.forename: M E
authors.initials: ME
authors.lastname: Tschakovsky
authors.forename: R L
authors.initials: RL
authors.lastname: Hughson
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001916:Brachial Artery / Q000033:anatomy & histology / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D005542:Forearm / Q000098:blood supply*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D012039:Regional Blood Flow / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology*