Blunted cerebral vascular responsiveness to hypercapnia in obese individuals.

What is the central question of this study? Is there a difference in the cerebral vascular response to rebreathing-induced hypercapnia between obese and lean individuals? What is the main finding and its importance? The main finding is that obese individuals have an attenuated increase in cerebral vascular conductance during hypercapnia relative to lean individuals. This finding suggests cerebral vascular dysfunction in this population, which might contribute to the greater prevalence of cerebral vascular and neurocognitive disease in this population. Obesity increases the risk of cardiovascular disease by >45%. Furthermore, obesity is a contributory factor to cognitive impairment and Alzheimer's disease. The mechanisms accounting for this increased disease risk have not been clarified. This study tested the hypothesis that the total range of change (a) in cerebral blood velocity (CBV) and cerebral vascular conductance (CVCI) and the maximal (y0) CBV and CVCI achieved during rebreathing-induced hypercapnia would be attenuated in obese individuals. Sixteen lean and 15 obese individuals participated. The magnitude of rebreathing-induced hypercapnia was similar between groups (lean, ∆15 ± 3 mmHg versus obese, ∆15 ± 2 mmHg; P = 0.82). The total range of change in CBV during rebreathing (a; expressed as a percentage) was similar between groups (lean, 91 ± 24% versus obese, 76 ± 19%, P = 0.07), whereas the total range of change in CVCI during rebreathing (a; expressed as a percentage) was attenuated in the obese individuals (lean, 71 ± 20% versus obese, 51 ± 15%, P < 0.01). Likewise, the maximal increase in CBV during rebreathing (y0; expressed as a percentage) was similar between groups (lean, 189 ± 22% versus obese, 179 ± 20%, P = 0.20), whereas the maximal increase in CVCI during rebreathing (y0; expressed as a percentage) was attenuated in the obese individuals (lean, 172 ± 19% versus obese, 155 ± 17 %, P = 0.01). These data indicate that the cerebral vascular response to rebreathing-induced hypercapnia is attenuated in obese individuals. This impairment might be a factor contributing to the elevated cerebral vascular and neurocognitive disease risk in this population.