Syncope is unrelated to supine and postural hypotension following prolonged exercise

Syncope is widely reported following prolonged exercise. It is often assumed that the magnitude of exercise-induced hypotension (post-exercise hypotension; PEH), and the hypotensive response to postural change (initial orthostatic hypotension; IOH) are predictors of syncope post-exercise. The aim of this study was to determine the relationship between PEH, IOH, the residual IOH and syncope following prolonged exercise. Blood pressure (BP; Finometer) was measured continuously in 19 athletes (47 +/- 20 years; BMI: 23.2 +/- 2.2 kg m(2); (V) over dotO(2) max: 51.3 +/- 10.8 mL kg(-1) min(-1)) whilst supine and during head-up tilt (HUT) to 60 degrees for 15 min (or to syncope), prior to and following 4 h of running at 70-80% maximal heart rate. Syncope developed in 15 of 19 athletes post-exercise [HUT-time completed, Pre: 14: 39 (min:s) +/- 0: 55; Post: 5: 59 +/- 4: 53; P < 0.01]. PEH was apparent (-7 +/- 7 mmHg; -8 +/- 8%), but was unrelated to HUT-time completed (r(2) = 0.09; P > 0.05). Although the magnitude of IOH was similar to post-exercise [-28 +/- 12 vs. -20 +/- 14% (pre-exercise); P > 0.05], the BP recovery following IOH was incomplete [-9 +/- 9 vs. -1 +/- 11 (pre-exercise); P < 0.05]; however, neither showed a relation to HUT-time completed (r(2) = 0.18, r(2) = 0.01; P > 0.05, respectively). Although an inability to maintain BP is a common feature of syncope post-exercise, the magnitude of PEH, IOH and residual IOH do not predict time to syncope. Practically, endurance athletes who present with greater hypotension are not necessarily at a greater risk of syncope than those who present with lesser reductions in BP.