title: Syncope is unrelated to supine and postural hypotension following prolonged exercise.
abstract: 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); VO(2) max: 51.3 ± 10.8 mL kg(-1) min(-1)) whilst supine and during head-up tilt (HUT) to 60° 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.
authors.affiliation: Department of Physiology, University of Otago, 270 Great King St, Dunedin, 9054, New Zealand. carissa.murrell@stonebow.otago.ac.nz
authors.forename: Carissa J
authors.initials: CJ
authors.lastname: Murrell
authors.forename: James D
authors.initials: JD
authors.lastname: Cotter
authors.forename: Keith
authors.initials: K
authors.lastname: George
authors.forename: Robert
authors.initials: R
authors.lastname: Shave
authors.forename: Luke
authors.initials: L
authors.lastname: Wilson
authors.forename: Kate
authors.initials: K
authors.lastname: Thomas
authors.forename: Michael J A
authors.initials: MJ
authors.lastname: Williams
authors.forename: Philip N
authors.initials: PN
authors.lastname: Ainslie
mesh_terms: D000328:Adult; D000368:Aged; D001794:Blood Pressure / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006801:Humans; D007024:Hypotension, Orthostatic / Q000150:complications* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D005082:Physical Exertion / Q000502:physiology*; D016683:Supine Position / Q000502:physiology*; D013575:Syncope / Q000209:etiology* / Q000503:physiopathology; D018667:Tilt-Table Test; D013997:Time Factors