Sympathetic modulation of blood flow and O2 uptake in rhythmically contracting human forearm muscles

M. J. Joyner, L. A. Nauss, M. A. Warner, D. O. Warner

Research output: Contribution to journalArticle

109 Scopus citations

Abstract

This study tested the effects of sympathetically mediated changes in blood flow to active muscles on muscle O2 uptake (V̇O2) in humans. Four minutes of graded (15-80% of maximum voluntary contraction, MVC) rhythmic handgrip exercise were performed. Forearm blood flow (FBF) (plethysmography) and deep vein O2 saturation were measured each minute. Forearm O2 uptake was calculated using the Fick principle. In protocol 1, exercise was performed while supine and again while upright to augment sympathetic outflow to the active muscles. Standing reduced FBF at rest from 3.6 to 2.2 ml · 100 ml-1 · min-1 (P < 0.05). During light exercise (15-40% MVC) FBF was unaffected by body position. Standing reduced FBF (P < 0.05) from 36.0 to 25.2 ml · 100 ml-1 · min-1 and forearm V̇O2 from 38.2 to 28.1 ml · kg-1 · min- 1 during the final work load. In protocol 2, exercise was performed while supine before and after local anesthetic block of the sympathetic nerves to the forearm. Sympathetic block increased FBF at rest from 3.1 to 8.9 ml · 100 ml-1 · min-1 (P < 0.05), and FBF was higher during all work loads. At 70-80% of MVC sympathetic block increased FBF from 35.4 to 50.7 ml · 100 ml-1 · min-1 (P < 0.05); and forearm V̇O2 from 45.5 to 54.2 ml · kg- 1 · min-1 (P < 0.05). These results suggest that in humans sympathetic nerves modulate blood flow to active muscles during light and heavy rhythmic exercise and that this restraint of flow can limit O2 uptake in muscles performing heavy rhythmic exercise.

Original languageEnglish (US)
Pages (from-to)H1078-H1083
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume263
Issue number4 32-4
DOIs
StatePublished - 1992

Keywords

  • blood pressure
  • exercise
  • muscle blood flow
  • muscle oxygen uptake

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

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