THE EFFECT OF POSTURE ON POST-EXERTIONAL HYPOTENSION AND STROKE VOLUME811

Abstract

Following dynamic exercise there is a decrease in mean arterial pressure(MAP) which may be mediated by a reduction in stroke volume or total peripheral resistance. The precise mechanism responsible for hypotension may be dependent upon the recovery posture adopted. This study was therefore designed to assess the blood pressure and central haemodynamic responses to both supine and seated recovery from maximal exercise. Baseline blood pressure(Finapres, USA), stroke volume and ventricular dimensions (Sonos 100, Hewlett-Packard, Andover) were measured 30 min prior to an incremental cycle test to exhaustion in seven male subjects after a written declaration of consent. This protocol was repeated on two occasions and followed by 60 min of recovery in either the seated or supine posture. After exercise, MAP decreased during both supine (-8±4 mmHg at 20 min recovery) and seated recovery(-7±2 mmHg at 20 min recovery) (P<0.05). During supine recovery there was no evidence of any impaired ventricular filling as stroke volume was slightly elevated due to an enhanced ventricular fractional shortening (P<0.01) and ejection fraction (P<0.01). The post-exercise tachycardia effectively maintained cardiac output above baseline levels in the supine position. Despite evidence of enhanced ventricular contractility, stroke volume was reduced throughout seated recovery (-14.3±3.5 ml - at 60 min recovery, P<0.05). In conclusion, although heart rate was elevated during seated recovery, the reduction of stroke volume was such that the contribution of cardiac output to the maintenance of blood pressure was compromised.