Effect of upright posture on central wave reflection in 637 volunteers not using medications with direct cardiovascular influences: Description of different phenotypes

Abstract

BackgroundThe effect of upright posture on the level of augmentation index (AIx) remains controversial [1–3]. Phenotypic differences in AIx responses to upright posture are unknown.MethodsAltogether 323 women and 315 men without cardiovascular disease and medications with direct cardiovascular influences were subjected to passive head-up tilt (5-min supine, 5-min upright). Haemodynamics were recorded using continuous tonometric pulse wave analysis and whole-body impedance cardiography.ResultsMean (SD) age was 45.6 (1.2) years, BMI 26.8 (4.4) kg/m2, and average blood count, plasma lipids and creatinine were normal. AIx decreased from supine 22.7% (11.9) to upright 13.8% (12.2) (p < 0.001), while heart rate related AIx@75 decreased from 17.9% (11.8) to 13.9% (11.0) (p < 0.001), respectively. In stepwise linear regression analyses, the explanatory variables for upright reduction in AIx were changes in ejection duration (β = 0.744), aortic reflection time (β = −0.491), and stroke volume (β = 0.117); and supine ejection duration (β = 0.312), systemic vascular resistance (SVR) (β = −0.271), pulse wave velocity (PWV) (β = −0.203), and systolic blood pressure (β = 0.081) (p≤0.001 for all). When divided to quartiles according to the supine-to-upright change in AIx 1) the quartile with lowest supine AIx had highest upright AIx, lowest supine SVR and PWV, and lowest upright heart rate; 2) the quartile with highest supine AIx had lowest upright AIx, highest supine SVR and PWV, and highest upright heart rate.ConclusionsThe level of AIx is decreased in the upright position. The phenotypic differences in the supine-to-upright change in AIx may explain why this variable has not predicted cardiovascular events in all endpoint studies.