Central arterial stiffness, flow-mediated dilation, and venous function in postural orthostatic tachycardia syndrome

Postural orthostatic tachycardia syndrome (POTS) is a debilitating disorder characterized by excessive increases in heart rate upon standing and poor orthostatic tolerance. Impairments in large artery, endothelial, and venous function may collectively, or individually, result in excessive blood pooling and impaired venous return, or other inadequate vascular response to standing, thus contributing to POTS. Herein, we tested the hypothesis that patients with POTS would exhibit reduced large artery stiffness, enhanced endothelial function, and greater lower limb venous pooling while standing, compared with healthy controls. Fourteen participants with a clinical diagnosis of POTS and 15 age-matched controls (all females; median age [interquartile range]; 21 [19-37] yr, <i>P</i> = 0.769) were recruited. Central arterial stiffness was determined using carotid-femoral pulse wave velocity (cfPWV; SphygmoCor). Endothelial function was assessed using brachial artery flow-mediated dilation (FMD) following a 5-min forearm occlusion at 200 mmHg. Functional measures of calf venous volume and filling time (90% maximal venous filling) were acquired (air plethysmography) while standing. cfPWV was increased in people with POTS [(means ± SD) 5.5 ± 0.9 vs. 4.8 ± 0.4, <i>P</i> = 0.031], whereas FMD was not different between groups (<i>P</i> = 0.854). During standing, calf venous volume was 29% greater in people with POTS (<i>P</i> = 0.048), and venous filling time was almost twice as long (404 ± 199 vs. 207 ± 99 s; <i>P</i> = 0.003). These findings indicate that people with POTS exhibit increased central arterial stiffness, preserved endothelial function, and increased calf venous filling during standing. Such differences in lower limb venous filling dynamics on standing likely contribute to the orthostatic intolerance that characterizes POTS.<b>NEW & NOTEWORTHY</b> Females with POTS and age-matched healthy controls underwent assessments of central arterial stiffness, endothelial function, and calf distensibility. Pulse wave velocity was higher in people with POTS, but brachial artery flow-mediated dilatation was not different between groups. Standing calf volume was greater in people with POTS, and maximal filling times were twice as long, suggesting altered venous and/or microvascular function. Augmented venous pooling in patients with POTS may impair venous return and orthostatic tolerance.