Consequences and countermeasures of sedentary behaviour on arterial wave reflection

Abstract

Cardiac load is directly influenced by central wave reflections, with increases in reflected wave magnitude and reductions in return time contributing to increased systolic pressure, afterload, and impaired coronary blood flow. Prolonged sitting has known vascular consequences such as increased arterial stiffness and endothelial dysfunction, yet the impact on wave reflections and efficacy of interruption methods to mitigate these effects is unknown. This study was designed to investigate whether seated elliptical exercise or standing breaks alleviated the deleterious effects of prolonged sitting on central wave reflections. Eighteen healthy adults (9 females, 25±3 years) completed three hours of uninterrupted sitting, sitting with periodic standing, and sitting with seated elliptical breaks, on separate days. Central and lower limb pulse wave velocity were measured before and after the intervention as well as central wave reflection which was calculated via pressure-flow analysis of aortic blood flow and carotid arterial pressure. A main effect of time was observed for forward wave amplitude (40.0±8.2 to 35.2±6.0 mmHg; p = 0.02) and reflected wave amplitude (11.9±1.6 to 11.3±2.0 mmHg; p = 0.03). Central relative wave reflection magnitude increased during sitting control (0.31±0.05 to 0.35±0.05; p < 0.01) but did not change with seated elliptical (0.30±0.05 to 0.30±0.04; p > 0.99) or standing breaks (0.30±0.05 to 0.32±0.04; p = 0.19). Augmentation index increased with sitting control (-9.3±9.2 to -4.6±12.2 %; p < 0.01) and standing (-12.4±9.8 to -5.6±9.4 %; p < 0.01), but not with seated elliptical (-9.9±9.4 to -10.2±11.1 %; p = 0.82. Lower limb pulse wave velocity did not change with sitting control (9.5±1.7 to 9.6±1.0 m·s-1; p = 0.73) or standing (9.1±1.5 to 9.7±1.7 m·s-1; p = 0.21) but decreased with seated elliptical (9.8±1.4 to 9.1±1.5 m·s-1; p = 0.03) Central pulse wave velocity increased during sitting control (5.3±0.8 to 5.7±0.9 m·s-1; p < 0.01) and standing (5.3±0.7 to 5.7±0.7 m·s-1; p < 0.01) but not with seated elliptical (5.5±0.5 to 5.6±0.6 m·s-1; p = 0.43). Prolonged sitting without interruptions increased central wave reflection, central pulse wave velocity, augmentation index, and decreased femoral blood flow while seated elliptical but not standing breaks were able to ameliorate these sitting-induced vascular consequences. Future work should examine the long-term effectiveness of interruption methods, as well as the optimal type, frequency, and duration for reducing CVD risk associated with sedentary behaviours.