Cardiorespiratory and cerebrovascular responses to head-up tilt I: influence of age and training status.

The purpose of this study was to examine the combined cardiorespiratory and cerebrovascular responses to head-up tilt (HUT) in young (27 ± 4 years) and older (65 ± 5 years) trained and untrained humans. Middle cerebral artery blood velocity (MCAv; transcranial Doppler ultrasound), blood pressure (BP; Finometer) and cardiac output (Q) 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]. Thirty seven of forty one participants completed 15 min HUT, and orthostatic tolerance did not differ with age or fitness (P = 0.66). Supine MCAv was 30% lower in the older participants but the HUT-induced drop in MCAv was not altered by age [-18% (young) vs. -17% (older)], or fitness. Mean arterial BP was maintained during HUT and not altered by age or fitness. In the untrained, peripheral resistance was elevated [11% vs. -2% (trained); P = 0.01], and Q was reduced [-10% vs. -5% (trained); P = 0.04] with HUT. Despite these age- and fitness-associated differences in some cardiovascular responses to HUT, orthostatic tolerance was similar across groups. Thus, at least in this healthy population, neither age nor fitness impacts on the ability to adapt to postural change.