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Am J Physiol Regul Integr Comp Physiol 281: R716-R722, 2001;
0363-6119/01 $5.00
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Vol. 281, Issue 3, R716-R722, September 2001

Predicting cerebral blood flow response to orthostatic stress from resting dynamics: effects of healthy aging

K. Narayanan1, James J. Collins1, Jason Hamner2, Seiji Mukai2,3,4, and Lewis A. Lipsitz2,3,4

1 Center for BioDynamics and Department of Biomedical Engineering, Boston University, 3 Beth Israel Deaconess Medical Center Gerontology Division, Rabb 417, and 4 Harvard Medical School, Division on Aging, Boston 02215; and 2 Hebrew Rehabilitation Center for Aged, Research and Training Institute, Boston, Massachusetts 02131

The transfer function relating arterial pressure (AP) to cerebral blood flow velocity (CBFV) during resting conditions has been used to predict the CBFV response to hypotension. We hypothesized that this approach could predict the CBFV response to posture change in elderly individuals if impaired autoregulation allowed changes in AP to be passively transferred to CBFV. AP (Finapres) and CBFV (middle cerebral artery transcranial Doppler) were measured in 10 healthy young (age 24 ± 1 yr) and 10 healthy elderly (age 72 ± 3 yr) subjects during 5 min of quiet sitting and 1 min of active standing while breathing was paced at 0.25 Hz. Transfer functions between AP and CBFV changes during sitting were estimated from each full waveform in both low-frequency (LF; 0.05-0.2 Hz) and heartbeat-frequency (HBF; 0.7-1.4 Hz) ranges. The impulse-response function was used to compute changes in CBFV during posture change. The LF transfer function did not predict orthostatic changes in CBFV in either group, suggesting normal cerebral autoregulation. In the HBF range, the prediction was high in elderly (R = 0.65 ± 0.23) but not young subjects (R = 0.19 ± 0.35; P < 0.003, young vs. elderly). Thus rapidly acting regulatory mechanisms that reduce the transmission of beat-to-beat changes in AP to CBFV may be engaged during posture change in young but not elderly subjects.

autoregulation; transfer function; hypotension; pulsatility; vascular stiffness


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