Extra- and intracranial blood flow regulation during the cold pressor test: influence of age.

We determined how the extra- and intracranial circulations respond to generalized sympathetic activation evoked by a cold pressor test (CPT) and whether this is affected by healthy aging. Ten young [23 ± 2 yr (means ± SD)] and nine older (66 ± 3 yr) individuals performed a 3-min CPT by immersing the left foot into 0.8 ± 0.3°C water. Common carotid artery (CCA) and internal carotid artery (ICA) diameter, velocity, and flow were simultaneously measured (duplex ultrasound) along with middle cerebral artery and posterior cerebral artery mean blood velocity (MCAv and PCAv) and cardiorespiratory variables. The increases in heart rate (6 beats/min) and mean arterial blood pressure (14 mmHg) were similar in young and older groups during the CPT ( < 0.01 vs. baseline). In the young group, the CPT elicited an 5% increase in CCA diameter ( < 0.01 vs. baseline) and a tendency for an increase in CCA flow (12%, = 0.08); in contrast, both diameter and flow remained unchanged in the older group. Although ICA diameter was not changed during the CPT in either group, ICA flow increased (~8%, = 0.02) during the first minute of the CPT in both groups. Whereas the CPT elicited an increase in MCAv and PCAv in the young group (by ~20 and ~10%, respectively, < 0.01 vs. baseline), these intracranial velocities were unchanged in the older group. Collectively, during the CPT, these findings suggest a differential mechanism(s) of regulation between the ICA compared with the CCA in young individuals and a blunting of the CCA and intracranial responses in older individuals. Sympathetic activation evoked by a cold pressor test elicits heterogeneous extra- and intracranial blood vessel responses in young individuals that may serve an important protective role. The extra- and intracranial responses to the cold pressor test are blunted in older individuals.