Extra and intra-cranial blood flow regulation during the cold pressor test: influence of age

We determined how the extra- and intra-cranial circulations respond to generalized sympathetic activation evoked by a cold pressor test (CPT) and whether this was affected by healthy aging. Ten young (23±2 yr; mean±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_mean and PCAv_mean), and cardiorespiratory variables. The increases in heart rate (~6 bpm) and mean arterial blood pressure (~14 mmHg) were similar in young and older groups during the CPT (P<0.01 vs. baseline). In the young group, the CPT elicited a ~5% increase in CCA diameter (P<0.01 vs. baseline) and tendency for an increase in CCA flow (~12%; P=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%; P=0.02) during the first minute of the CPT in both groups. While the CPT elicited an increase in MCAv_mean and PCAv_mean in the young group (by ~20% and ~10%, respectively; P<0.01 vs. baseline), these intra-cranial velocities were unchanged in the older group. Collectively, during the CPT, these findings suggest a differential mechanism(s) of regulation between the ICA compared to the CCA in young individuals, and a blunting of the CCA and intra-cranial responses in older individuals.

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