Hypoxia, hypercapnia, and hypertension: their effects on pulsatile cerebral blood flow. Curran-Everett, Douglas, Yiming Zhang, Richard H. Jones, and M. Douglas Jones, Jr. Departments of Pediatrics and Preventive Medicine and Biometrics University of Colorado Health Sciences Center, Denver, CO 80262
APStracts 2:0179A, 1995.
Pulsatile cerebral blood flow reflects characteristics of arterial blood pressure as well as the structure and mechanical properties of the cerebrovascular network. Although effects of changes in systemic blood gases and blood pressure on mean cerebral flow are established, their effects on pulsatile cerebral blood flow are unknown. These studies assessed the effects of hypoxia/hypercapnia (combined; both PaO2 and PaCO2 sim 55 mmHg ) and acute hypertension (+30--35 mmHg by aortic occlusion) on pulsatile cerebral blood flow in ketamine -anesthetized rabbits. We characterized the relationship between pulsatile systemic blood pressure (Millar catheter) and cerebral cortical capillary blood flow (laser-Doppler) by calculating the transfer function, a frequency-domain expression that relates amplitudes and phase angles of flow output to those of the pressure input. During hypoxia/hypercapnia, mean flow increased 17% ( P < 0.001 ) but the amplitude and contour of pulsatile cortical blood flow were unchanged ( P > 0.10 ). Although aortic occlusion-- -during hypoxia/hypercapnia as well as normoxia/normocapnia-- -increased systemic pulse pressure by 40%, the amplitude of cortical flow pulsations was unaffected. Changes in dynamic properties of the cerebral vasculature ( P < 0.0001 by analysis of the transfer function) minimized alterations in pulsatile cortical blood flow and thus, intra-beat vessel wall stress during acute hypertension; based on analysis of an electrical analog, we propose that these changes reflect alterations in both resistance and compliance. 

Received 27 January 1995; accepted in final form 24 April 1995.
APS Manuscript Number A106-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  2 May 1995.