title: Cardiorespiratory and cerebrovascular responses to head-up tilt II: influence of age, training status and acute exercise.
abstract: The purpose of this study was to examine the combined cardiorespiratory and cerebrovascular responses to head-up tilt (HUT) in young and older trained and untrained humans following moderate-duration exercise. Middle cerebral artery blood flow velocity (MCAv; transcranial Doppler ultrasound), blood pressure (BP; Finometer), and stroke volume (SV) were measured continuously whilst supine and during 60° HUT for 15 min or to pre-syncope in 41 participants [nine young trained; eleven young untrained; twelve older trained; nine older untrained] prior to and following 30 min of treadmill exercise at 70-80% maximal HR. Orthostatic tolerance was not reduced following exercise [Mean (all groups) 14:45 ± 1:19, vs. 14:47 ± 0:43 min:s (before exercise); P = 0.73], and did not differ with age or fitness. Mean MCAv was elevated [~5 ± 11%] whilst supine after exercise in the older participants but reduced [~-4 ± 12%] in the young [P = 0.03]. The postural reductions in MCAv [~-22% vs. -17%; P = 0.02], MAP [~-8% vs. -3%; P = 0.04] and SV [~-28% vs. -23%; P = 0.03] were increased after exercise (vs. pre-exercise). Orthostatic tolerance was not reduced following 30 min of exercise, and did not differ with age or fitness, despite more pronounced post-exercise reductions in MCAv, MAP and SV with postural change.
authors.affiliation: Department of Physiology, University of Otago, Dunedin, New Zealand.
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; D000375:Aging / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002320:Cardiovascular Physiological Phenomena; D002560:Cerebrovascular Circulation / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000502:physiology; D054971:Orthostatic Intolerance / Q000503:physiopathology*; D010809:Physical Fitness / Q000502:physiology*; D012143:Respiratory Physiological Phenomena; D013318:Stroke Volume / Q000502:physiology; D016683:Supine Position / Q000502:physiology; D018667:Tilt-Table Test; D055815:Young Adult