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Cerebrovascular carbon dioxide reactivity and flow mediated dilation in young healthy South Asian and Caucasian European men.

South Asians living in the UK have a 1.5-fold greater risk of ischemic stroke than the general population. Impaired cerebrovascular carbon dioxide (CO2) reactivity is an independent predictor of ischemic stroke and cardiovascular mortality. We sought to test the hypothesis that cerebrovascular CO2 reactivity is reduced in South Asians. Middle cerebral artery blood velocity (MCA Vm) was measured at rest and during stepwise changes in partial pressure of end-tidal CO2 (PETCO2) in South Asian (n=16) and Caucasian European (n=18) men that were, young (~20 years), healthy and living in the UK. Incremental hypercapnia was delivered via the open circuit steady-state method, with stages of 4% and 7% CO2 (≈21% Oxygen, Nitrogen balanced). Cerebrovascular CO2 reactivity was calculated as the change in MCA Vm per mmHg change in PETCO2. MCA Vm was not different in South Asian (59 (9) cm/s; mean (standard deviation)) and Caucasian Europeans (61 (12) cm/s; P>0.05). Similarly, cerebrovascular CO2 reactivity was not different between the groups (South Asian, 2.53 (0.76) cm/s/mmHg vs. Caucasian European, 2.61 (0.81) cm/s/mmHg; P>0.05). Brachial artery flow-mediated dilatation was lower in South Asian (5.48 (2.94) %) compared to Caucasian European (7.41 (2.28) %; P<0.05); however when corrected for shear rate, no between group differences in flow-mediated dilatation were observed (P>0.05). Flow-mediated dilation was not correlated with cerebrovascular CO2 reactivity measures. In summary, cerebrovascular CO2 reactivity and flow-mediated dilation when corrected for shear rate are preserved in young healthy South Asian men living in the UK.