Abstract
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.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.