Reliability of Vasodilation in Response to Passive Leg Movement in Young, Healthy Women
Passive leg movement (PLM) elicits rapid vasodilation and an increase in blood flow, that is dependent on the function of the endothelial cells that line the small arteries in the leg. The increased flow therefore provides an index of endothelial function in the lower-limb microvasculature. This index has identified alterations in endothelial function in advanced aging and clinical populations, demonstrating that the vasodilatory response to PLM provides a useful assessment of vascular responses. Understanding the day-to-day variation in arterial responses is important when distinguishing meaningful changes in endothelial function, however, there is currently limited information regarding the reliability of PLM-induced vasodilation. It was expected that performing three trials of PLM on two separate days would allow for a robust quantification of day-to-day reliability. Seventeen, young healthy women (22 +/- 3 years) participated in two identical experimental visits during the low-estrogen menstrual phase. Endothelial function was assessed each visit by conducting three trials of PLM. The reliability of PLM-induced vasodilation was quantified by calculating the Pearson correlation coefficient (r value), intraclass correlation coefficient (ICC) and coefficient of variation (CV). Additionally, typical error (TE) was calculated for future identification of individual differences in response to an intervention. The results demonstrated good reliability of the vasodilatory response to PLM characterized as peak leg blood flow (LBF; r = 0.84, ICC = 0.84, CV = 13.2%) and leg vascular conductance (LVC; r = 0.82, ICC = 0.79, CV = 14.4%), and change from baseline to peak LBF (r = 0.83, ICC = 0.82, CV = 17.8%) and LVC (r = 0.83, ICC = 0.80, CV = 16.5%). Characterization of PLM as change in area under the curve (AUC) was less reliable than the other PLM measures; AUC LBF (r = 0.71, ICC = 0.70, CV = 31.2%) and AUC LVC (r = 0.78, ICC = 0.74, CV = 27.1%). This is the first full study to evaluate the reliability of PLM-induced vasodilation, demonstrating that it provides a reliable assessment of lower-limb microvascular endothelial function. These findings will support future studies aiming to classify meaningful individual vascular responses in women.