Regional cerebral autoregulation during orthostatic stress: Age-related differences

Background. We used transcranial Doppler ultrasonography to examine the cerebral blood flow response to orthostatic stress in the middle and posterior cerebral circulations and to determine the effects of healthy aging on regional cerebral blood flow regulation. Methods. Continuous simultaneous middle (MCA) and posterior (PCA) cerebral artery blood flow velocities (BFV) and mean arterial pressure (MAP) were measured in response to standing from a sitting position in 13 younger (30 ± 7 years) and 13 older (73 ± 4 years) healthy participants. Results. The older participants had a significantly larger decline in MAP (-31% ± 3 in the older and -21% ± 2 in the younger) and a smaller increase in heart rate (HR) (15 bpm ± 1 in the older. 24 bpm ± 2 in the younger) during the posture change. Despite a larger decline in MAP, the older participants had a decline very similar to that of the younger participants in BFVs in both vascular territories. This was associated with a significantly larger vasodilatory response in the MCA and PCA vascular territories of the older participants. There were no regional differences of the cerebrovascular resistance and BFV responses to orthostasis in the younger participants. However, in the older participants, there was a significantly larger BFV decline and a smaller vasodilatory response in the PCA as compared to the MCA territory. Conclusions. Healthy aging is associated with preserved cerebrovascular adaptation to orthostatic hypotension. However, in older persons, the PCA territory blood flow may be more vulnerable to reduced perfusion during orthostatic stress.