Attenuated cerebral vasodilatory capacity in response to hypercapnia in college‐aged African Americans

Abstract

African Americans (AAs) have increased risk for cardiovascular, cerebral vascular and metabolic disease, including hypertension, stroke, coronary artery disease, metabolic syndrome and type II diabetes, relative to Caucasian Americans (CAs). While it is accepted that endothelial function is impaired in AAs, less is known regarding their cerebral vasodilatory capacity in response to hypercapnia. We hypothesized that AAs have a reduction in the total range of change in cerebral blood flow velocity (CBFV) measured in the middle cerebral artery and an index of cerebral vascular conductance (CVCI) in response to changes in the partial pressure of end-tidal carbon dioxide () during rebreathing-induced hypercapnia when compared with CAs. Twenty-one healthy, college-aged AA (10 male) and 21 age- and sex-matched CA (10 male) subjects participated in this study. A four-parameter logistic regression was used for curve fitting the responses of CBFV and CVCI relative to changes in . The total ranges of change in CBFV (101 ± 18 versus 69 ± 23%; P < 0.001) and CVCI (83 ± 21 versus 58 ± 21%; P < 0.001) as well as the maximal increase in CBFV (205 ± 24 versus 169 ± 24%; P < 0.001) and CVCI (188 ± 30 versus 154 ± 19%; P < 0.001) were reduced during hypercapnia in AAs relative to CAs despite a similar increase in (change, 15 ± 3 versus 15 ± 3 mmHg; P = 0.65). In conclusion, these data indicate that AAs have attenuated cerebral vascular capacity to respond to hypercapnia when compared with CAs.

Genes count: attenuated cerebral vasodilator capacity in young African Americans

“…If similar dysfunction exists in the cerebral circulation of African Americans, it could impair cerebral blood flow regulation and predispose to, or possibly trigger, cerebrovascular events. The evidence reported in this issue of Experimental Physiology by Hurr et al (2014) of impaired cerebral vascular vasodilator capacity in response to CO 2 in college-aged African Americans supports such considerations. Hurr et al (2014) show that young, healthy African Americans exhibit a reduced cerebrovascular vasodilatory response to CO 2 when compared with Caucasian American students.…”

“…The evidence reported in this issue of Experimental Physiology by Hurr et al (2014) of impaired cerebral vascular vasodilator capacity in response to CO 2 in college-aged African Americans supports such considerations. Hurr et al (2014) show that young, healthy African Americans exhibit a reduced cerebrovascular vasodilatory response to CO 2 when compared with Caucasian American students. Using transcranial Doppler ultrasonography, they imaged the right middle cerebral artery (MCA) during a rebreathing protocol that elevated end-tidal CO 2 by 15 mmHg, while a small amount of oxygen was added to the rebreathing bag to prevent arterial desaturation.…”

“…Although it is acknowledged that the study by Hurr et al (2014) presents data from only one blood vessel and that CO 2 sensitivity may differ between cerebral vessels (Sato et al 2012), it seems that an attenuated cerebrovascular vasodilatory response to CO 2 exists among young, healthy African Americans.…”

“…Most importantly, perhaps, would be a greater understanding of whether attenuated cerebrovascular vasodilatory capacity is a predictor of future clinical events and, if so, could appropriate intervention be initiated based on screening, e.g. by the relatively simple protocol that was used by Hurr et al (2014)? Obviously, the observations of Hurr et al (2014) need confirmation by more sophisticated evaluation of cerebral blood flow, including advanced scanning techniques and further investigation of regional differences.…”

“…by the relatively simple protocol that was used by Hurr et al (2014)? Obviously, the observations of Hurr et al (2014) need confirmation by more sophisticated evaluation of cerebral blood flow, including advanced scanning techniques and further investigation of regional differences. Considering the prevalence of stroke among African Americans, however, the importance of the study is that it initiates an evaluation of cerebrovascular responses in this population.…”