Abstract

Objective: To investigate the regulation of blood pressure in response to an orthostatic challenge in athletes running a marathon.

Methods: Ten experienced male runners (mean ± SD age 29 ± 4 years) were tested on the day prior to the 2004 London Marathon, and again immediately post-race (race time 210 ± 36 min). In addition, 6 of the subjects were re-tested 24 hours post-race. During each examination, systolic arterial blood pressure (SBP), heart rate (HR) were measured, and stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR) were estimated via arterial transmural pressure waveforms during 3 min in a supine position and then during 3 min of upright, unsupported standing. Data were averaged over 20 s epochs, and the final 20 s of each posture were compared pre- and post-race via repeated measures 2-way ANOVA.

Results: Pre-race SBP in standing increased only moderately when compared to supine values (2 ± 9 mmHg, P>0.05). This was accompanied by an increase in HR (13 ± 7 beats.min-1, P<0.05), and as well as a decrease in SV (16 ± 9 ml, P<0.05). However there was little change in CO (-0.13 ± 0.97 l.min-1, P>0.05) or TPR (0.047 ± 0.280 MU, P>0.05). Post-race SBP significantly decreased from supine to standing (-15 ± 20 mmHg, P<0.05). The change in SBP was accompanied an increase in HR (19 „b 6 beats.min-1, P<0.05), a reduction in SV (26 ± 14 ml, P<0.05) and CO (-1.02 ± 1.39 l.min-1, P=0.05). Post-race there was no change in TPR (0.366 ± 0.607 MU, P>0.05) upon standing. The orthostatic adjustments in SBP, HR and CO were greater than at pre-race (P<0.05). The post-race orthostatic challenge resulted in only one subject experiencing presyncopal symptoms. At 24 hr post-race cardiovascular responses to an orthostatic challenge mirrored those at pre-race.

Conclusions: A drop in systolic blood pressure upon orthostatic challenge after prolonged exercise appears to result from an uncompensated decrease in SV and resultant CO during standing.