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1 Research & Training Institute, Hebrew Rehabilitation Center for Aged, Boston, MA, USA; Department of Gerontology, Beth Israel Deaconess Medical Center, Boston, MA, USA; Division on Aging, Harvard Medical School, Boston, MA, USA
2 Research & Training Institute, Hebrew Rehabilitation Center for Aged, Boston, MA, USA; Department of Neurology, Brigham and Women's Hospital, Boston, MA, USA; Division on Aging, Harvard Medical School, Boston, MA, USA
3 Division on Aging, Harvard Medical School, Boston, MA, USA
4 Research & Training Institute, Hebrew Rehabilitation Center for Aged, Boston, MA, USA; Division on Aging, Harvard Medical School, Boston, MA, USA; Department of Gerontology, Beth Israel Deaconess Medical Center, Boston, MA, USA
* To whom correspondence should be addressed. E-mail: serrador{at}hms.harvard.edu.
The dynamics of the cerebral vascular response to blood pressure changes in hypertensive humans is poorly understood. Since cerebral blood flow is dependent on adequate perfusion pressure, it is important to understand the effect of hypertension on the transfer of pressure to flow in the cerebrovascular system of elderly people. Therefore, we examined the effect of spontaneous and induced blood pressure changes on beat-to-beat and within beat cerebral blood flow in three groups of elderly people; normotensive, controlled hypertensive, and uncontrolled hypertensive subjects. Cerebral blood flow velocity (transcranial Doppler), blood pressure (finapres), heart rate and end-tidal CO2 were measured during the transition from a sit to stand position. Transfer function gains relating blood pressure to cerebral blood flow velocity were assessed during steady state sitting and standing. Cerebral blood flow regulation was preserved in all three groups using changes in cerebrovascular resistance, transfer function gains, and the autoregulatory index as indices of cerebral autoregulation. Hypertensive subjects demonstrated better attenuation of cerebral blood flow fluctuations in response to blood pressure changes both within the beat (i.e. lower gain at the cardiac frequency) and in the low frequency range (autoregulatory, 0.03-0.07 Hz). Despite a better pressure autoregulatory response, hypertensive subjects demonstrated reduced reactivity to carbon dioxide. Thus, otherwise healthy hypertensive elderly subjects, whether controlled or uncontrolled with anti-hypertensive medication, retain the ability to maintain cerebral blood flow in the face of acute changes in perfusion pressure. Pressure regulation of cerebral blood flow is unrelated to cerebrovascular reactivity to CO2.
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