Poster Communications: Global Reach 2018: High altitude acclimatisation improves neurovascular coupling in man

Neurovascular coupling (NVC) is responsible for the close temporal and regional linkage of cerebral blood supply to local cerebral metabolic requirements. The present study sought to examine the influence of acute simulated high altitude (SHA) and high altitude acclimatisation (HAA) on NVC in seven healthy male lowlanders (aged 28 ± 8 years). NVC was assessed at three time points: sea level (344m); after 30 minutes of dynamic end-tidal forcing to simulate an equivalent altitude of ~4,300m (SHA) and after two weeks acclimatisation to the same altitude (HAA, Cerro de Pasco, Peru). Posterior cerebral artery blood velocity (PCAv) was assessed using transcranial Doppler ultrasound during five consecutive trials of 30s eyes open with standardised visual stimulation (flashing checkerboard), followed by 30s of eyes closed. The NVC response was characterised as the percent peak and average increase (relative to eyes closed) in PCAv during 25s of visual stimulation, averaged across the five trials. Distribution normality was confirmed by Shapiro Wilks W tests and data analysed using a repeated measures ANOVA. Significance was set at P < 0.05. SHA attenuated both peak (10 ± 2% vs. 18 ± 4%, P = 0.021) and average percent increases in PCAv (3 ± 2% vs. 8 ± 3%, P = 0.015) compared to sea level. Despite similar reductions in arterial oxygen saturation and partial pressures of oxygen and carbon dioxide, HAA increased both peak (25 ± 7% vs. 18 ± 4%, P = 0.016) and average (13 ± 5% vs. 8 ± 3%, P = 0.045) percent increases in PCAv during visual stimulation, when compared to sea level. The differential response of NVC to SHA and HAA (reduction and increase, respectively) may reflect influences of acid base status and nitric oxide availability considering their differences between conditions.