Hypoxia changes the regional distribution of cerebral blood flow and stimulates the ventilatory chemoreflex, thereby reducing CO2 tension. We examined the effects of both hypoxia and isocapnic hypoxia on acute changes in internal carotid (ICA) and vertebral artery (VA) blood flow. Ten healthy male subjects underwent the following two randomly assigned respiratory interventions after a resting baseline period with room air: (i) hypoxia; and (ii) isocapnic hypoxia with a controlled gas mixture (12% O2; inspiratory mmHg). In the isocapnic hypoxia intervention, subjects were instructed to maintain the rate and depth of breathing to maintain the level of end-tidal partial pressure of CO2 ( ) during the resting baseline period. The ICA and VA blood flow (velocity × cross-sectional area) were measured using Doppler ultrasonography. The was decreased (-6.3 ± 0.9%, P < 0.001) during hypoxia by hyperventilation (minute ventilation +12.9 ± 2.2%, P < 0.001), while was unchanged during isocapnic hypoxia. The ICA blood flow was unchanged (P = 0.429), while VA blood flow increased (+10.3 ± 3.1%, P = 0.010) during hypoxia. In contrast, isocapnic hypoxia increased both ICA (+14.5 ± 1.4%, P < 0.001) and VA blood flows (+10.9 ± 2.4%, P < 0.001). Thus, hypoxic vasodilatation outweighed hypocapnic vasoconstriction in the VA, but not in the ICA. These findings suggest that acute hypoxia elicits an increase in posterior cerebral blood flow, possibly to maintain essential homeostatic functions of the brainstem.

译文

缺氧改变脑血流的区域分布,刺激通气化学反射,从而降低CO2张力。我们检查了缺氧和异血管缺氧对颈内动脉 (ICA) 和椎动脉 (VA) 血流急性变化的影响。10名健康男性受试者在静息基线期后接受了以下两种随机分配的呼吸干预措施: (i) 缺氧; 和 (ii) 用受控气体混合物 (12% O2; 吸气mmHg) 进行等缺血缺氧。在等缺血缺氧干预中,指导受试者在静息基线期间维持呼吸速率和呼吸深度以维持CO2 () 的潮气末分压水平。使用多普勒超声检查测量ICA和VA血流 (速度 × 横截面积)。在过度通气 (分钟通气 + 12.9 ± 2.2%,P <0.001) 的缺氧期间降低 (-6.3 ± 0.9%,P <0.001),而在等缺血缺氧期间保持不变。缺氧时ICA血流量不变 (P = 0.429),VA血流量增加 (+ 10.3 ± 3.1%,P = 0.010)。相反,等缺血缺氧增加了ICA (14.5 ± 1.4%,P <0.001) 和VA血流 (10.9 ± 2.4%,P <0.001)。因此,在VA中,低氧的血管舒张作用超过了低碳酸的血管收缩,但在ICA中却没有。这些发现表明,急性缺氧会引起大脑后部血流量的增加,可能会维持脑干的基本稳态功能。

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