Cardiovascular health, disease and function: Contributions of stress and diet, and consequences of type 2 diabetes
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Identifying the contributions to, and consequences of, impaired cardiovascular health and function is critical to inform effective prevention and treatment strategies. Mental stress and a high-fat diet are independent predictors of cardiovascular disease, and impaired vascular endothelial function (assessed via flow-mediated dilation; FMD) may be a common mechanistic link. Exercise can mitigate cardiovascular risk, but cardiovascular dysfunction (i.e. impaired oxygen delivery) can reduce exercise tolerance and decrease adherence. This may be characteristic of persons with Type 2 Diabetes (T2D), but this has never been investigated within the typical constellation of co-morbidities and associated medications in this population. PURPOSE: 1) To evaluate whether the combined experience of mental stress and fat consumption (versus either stimulus alone) exacerbates: postprandial lipemia, stress responsiveness, and endothelial dysfunction. 2) To determine whether T2D (within the typical cluster of co-morbidities and medications) results in impaired exercising muscle oxygen delivery and associated reduced small muscle mass exercise tolerance. METHODS: In healthy persons, FMD was assessed before and hourly for 4-hours post-consumption of a high-fat or low-fat meal, with hourly mental stress (mental arithmetic, speech) or control (counting) tasks. In persons with T2D and matched Controls, forearm critical force (fCFimpulse) was used as an indicator of exercise tolerance; exercising muscle blood flow was measured during fCFimpulse and during the adjustment and steady state of submaximal rest-to-exercise and exercise-to-exercise transitions. Ultrasound was used to measure FMD and exercising muscle blood flow. RESULTS: 1) Repeated mental stress tasks did not impact postprandial lipemia following either meal; 2) Meal fat content did not influence hemodynamic stress responsiveness; 3) Meal fat content did not affect FMD, but endothelial function was modestly greater when the postprandial state was accompanied by mental stress; 4) Relative to matched Controls, representative persons with T2D did not have impaired small muscle mass exercise tolerance (fCFimpulse) or muscle blood flow (rate of adjustment, or amount during submaximal/maximal steady state). CONCLUSIONS: These findings challenge the assertions that mental stress and fat consumption are universally detrimental, and that T2D, on top of the typical constellation of co-morbidities and medications, has an impact on exercising muscle blood flow and exercise tolerance.