Heating-induced peripheral limb microvascular vasodilation reduces arterial wave reflection

Abstract

Arterial wave reflection augments cardiac afterload increasing myocardial demands. Mathematical models and comparative physiology suggest that the lower limbs are the primary source of reflected waves; however, in vivo human evidence corroborating these observations is lacking. This study was designed to determine whether the vasculature of the lower or upper limbs contributes more to wave reflection. We hypothesized that lower limb heating will result in larger reductions in central wave reflection compared to upper limb heating due to local vasodilation of a larger microvascular bed. Fifteen healthy adults (8 females, 24±3.6 years) completed a within-subjects experimental crossover protocol with a washout period. The right upper and lower limbs were heated in a randomized order using 38°C water-perfused tubing with a 30-minute break between protocols. Central wave reflection was calculated using pressure-flow relationships derived from aortic blood flow and carotid arterial pressure at baseline and after 30 minutes of heating. We observed a main effect of time for reflected wave amplitude (12.8±2.7 to 12.2±2.6 mmHg; p=0.03) and augmentation index (-7.5±8.9 to -4.5±9.1%; p=0.03). No significant main effects or interactions were noted for forward wave amplitude, reflected wave arrival time, or central relative wave reflection magnitude (all p>0.23). Unilateral limb heating reduced reflected wave amplitude; however, the lack of a difference between conditions does not support the hypothesis that the lower limbs are the primary source of reflection. Future investigations should consider alternative vascular beds, such as the splanchnic circulation.