Effects of heel raising maneuver on hemodynamic and autonomic responses to the upright posture

Abstract

We investigated the effects of muscle pump function on hemodynamic and autonomic responses by heel raising maneuver (HRM) with four frequencies of 6, 7.5, 10, and 15 cycles/min in healthy subjects. Shortening of R-R interval during standing was suppressed by HRM. HRM at frequency of 10 cycles/min led to increase in stroke volume and decrease in total peripheral resistance. HRM at frequencies of 6 and 7.5 cycles/min induced increases in low-frequency powers of R-R interval and systolic blood pressure. The results indicate there is frequency-dependent effect of muscle pump function. I. INTRODUCTION Voluntary contraction of lower-leg muscles is very effective at reducing venous pooling during quiet standing (1). We previously demonstrated that application of lower-leg rhythmic cuff inflation with the pressures > 40 mmHg as a simulation of muscle pump function increased stroke volume and attenuated vagal withdrawal during the transition from sitting to standing (2). In this study we sought to determine how the frequency of muscle pump action (heel raising maneuver) influences hemodynamic and autonomic responses during standing. II. MATERIALS AND METHODS Eight healthy young subjects (5 males and 3 females) aged 22.0¶ 0.5 yr were recruited. Subject wore a breathing mask on which a hot-wire flow meter was mounted. Disposable electrodes were placed on the chest and left gastrocnemius muscle for obtaining ECG and EMG, respectively. A Finapres sensor was placed around the index finger of the subject's left hand. After 4-min of sitting rest, subject performed heel raising maneuver (HRM) with 6 (HRM6), 7.5 (HRM7.5), 10 (HRM10), and 15 (HRM15) cycles/min in a standing position for 6 min. Quiet standing without HRM was served as a control (CTL). Continuous finger BP, respiratory flow, ECG, and EMG were measured. To minimize hemodynamic changes, these variables were recorded during paced breathing at 0.25 Hz. domain measures of variations of HR (HRV) and SBP (SBPV), a power spectral analysis was performed based on Welch's averaged periodogram technique. The total spectral power was calculated for the low (LF: 0.04-0.15 Hz) and high (HF: 0.15-0.4 Hz)-frequency bands by integration of the spectral components. Statistical significance was evaluated by a one-way analysis of variance followed by Dunnett's t-test.