Abstract
To assess racial, sexual, and regional differences in cerebral hemodynamic response to high altitude (HA, 3658 m). We performed cross-sectional comparisons on total cerebral blood flow (TCBF = sum of bilateral internal carotid and vertebral arterial blood flows = QICA + QVA), total cerebrovascular resistance (TCVR), total cerebral oxygen delivery (TCOD) and QVA/TCBF (%), among six groups of young healthy subjects: Tibetans (2-year staying) and Han (Han Chinese) at sea level, Han (2-day, 1-year and 5-year) and Tibetans at HA. Bilateral ICA and VA diameters and flow velocities were derived from duplex ultrasonography; and simultaneous measurements of arterial pressure, oxygen saturation, and hemoglobin concentration were conducted. Neither acute (2-day) nor chronic (>1 year) responses showed sex differences in Han, except that women showed lower TCOD compared with men. Tibetans and Han exhibited different chronic responses (percentage alteration relative to the sea-level counterpart value) in TCBF (−17% vs. 0%), TCVR (22% vs. 12%), TCOD (0% vs. 10%) and QVA/TCBF (0% vs. 2.4%, absolute increase), with lower resting TCOD found in SL- and HA-Tibetans. Our findings indicate racial but not sex differences in cerebral hemodynamic adaptations to HA, with Tibetans (but not Han) demonstrating an altitude-related change of CBF distribution.
Highlights
Differences among all 4 Han groups were assessed using one-way analysis of variance (ANOVA), with the LSD test used for post-hoc pairwise comparisons on the parameters in women and men (Table 1), or on CBF in bilateral ICAs and vertebral artery (VA) (Fig. 2A), separately
This helped to assess the effects of short- and long-term HA exposures on the Han lowlanders
A 2-way ANOVA with repeated-measures general linear model (GLM) was further performed in Tibetan SL and HA groups to examine the regional difference of CBF response to long-term HA exposure, as reflected by the interaction of 2(Altitude) × 2(Region)
Summary
All groups were similar in demographic features except that the Han-HA-5 yr group was ~2–4 years older than the other groups (Table 1), which was expected because the Han-HA-5yr included veteran soldiers while the other HA groups were new soldiers. When analyzed as a global bilateral measure, VA appeared to have a slightly greater increase in CBF than ICA (17% vs 15%, relative to the SL counterpart values) under short-term HA exposure (P = 0.02 indicated by the 2-way ANOVA; Fig. 2A); the comparisons on QVA/TCBF among different altitude groups showed no significant differences (Table 1 and Fig. 2C). The resting TCOD [ml O2/min] showed both race and sex differences (lower in Tibetans and females) at either SL or HA, but kept unchanged in Tibetans and significantly increased in Han (11% in females, and 9% in males, P = 0.03) at HA, with comparison to the SL counterpart value (Table 2 and Fig. 3).
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