Carotid baroreflex responsiveness to head-up tilt-induced central hypovolaemia: effect of aerobic fitness

J Physiol. 2003 Sep 1;551(Pt 2):601-8. doi: 10.1113/jphysiol.2003.046029. Epub 2003 Jun 17.


This investigation examined the interaction between carotid baroreflex (CBR) responsiveness during head-up tilt (HUT)-induced central hypovolaemia and aerobic fitness. Seven average fit (AF) individuals, with a mean maximal oxygen uptake (VO2max) of 49 +/- 1 (ml O2) kg-1 min-1, and seven high fit (HF) individuals, with a VO2max of 61 +/- 1 (ml O2) kg-1 min-1, voluntarily participated in the investigation. After 10-15 min supine, each subject was exposed to nine levels of progressively increasing HUT by 10 deg increments from -20 deg to +60 deg. During the final 3 min of each stage of HUT, the CBR responsiveness was measured using a rapid pulse (500 ms) train of neck pressure (NP) and neck suction (NS) ranging from +40 to -80 Torr. The maximal gain of the carotid-HR (Gmax-HR) and carotid-MAP (Gmax-MAP) baroreflex function curves was identified as measures of CBR responsiveness. During HUT-induced decreases in thoracic admittance, an index of central blood volume (CBV), the Gmax-HR and Gmax-MAP of the AF subjects increased more than the Gmax-HR and Gmax-MAP of the HF subjects (P < 0.05). The data demonstrate that the increase in the CBR responsiveness during a tilt-induced progressive unloading of the cardiopulmonary baroreceptors was attenuated in endurance-trained subjects. These findings provide an explanation for the predisposition to orthostatic hypotension and intolerance in well-trained athletes.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Anaerobic Threshold / physiology
  • Baroreflex / physiology*
  • Blood Pressure / physiology
  • Carotid Body / physiology*
  • Exercise / physiology
  • Heart Rate / physiology
  • Humans
  • Hypovolemia / physiopathology*
  • Male
  • Physical Endurance / physiology
  • Physical Fitness / physiology*
  • Posture / physiology*