A026: Diastolic filling as a determinant of exercise performance in older hypertensive patients

Abstract

We have previously described improved resting left ventricular diastolic filling (LVDF) and oxygen uptake (VO₂) kinetics during sub-ventilatory threshold (T_VT) exercise perturbations, under a variety of conditions in older hypertensive patients. To characterize LVDF as a primary determinant of exercise limitation in older hypertensive patients, we have simultaneously measured LVDF parameters with Doppler echocardiography and breath-by-breath gas exchange VO₂ kinetics during supine exercise at 70% T_VT in the current study. Thirty mild-moderate hypertensive men (mean 76 ± 7y) were studied before and 16 weeks following treatment to goal <160/90 (mean 144 ± 11/74 ± 7) with verapamilSR. Doppler studies included early:late filling ratio (E:A) and isovolumic relaxation time (IVRT) and VO₂ kinetics included the time constant (τ) of the on-transient exercise response. Baseline studies were done without medication (mean clinic blood pressure 171± 6/91 ± 4) while treatment consisted of single daily verapamilSR 240 mg. Studies were done in the left lateral decubitus position with 30° head up tilt for optimal imaging on an American Echo^™ supine ergometer. Resting Doppler studies using a Hewlett-Packard sonos 2000 imaging unit were followed by 2 square wave exercise perturbations. Following 6 min loadless pedaling at 60 rpm, the work rate was instantaneously increased to a work rate corresponding to 70% T_VT (determined from a maximal supine exercise test prior to the study) for 6 min. This was repeated twice. Expired gases were sampled every 10 m sec using a Perkin-Elmir mass spectrometer and stored on a microcomputer for analysis while Doppler images using a 2.5 MHz transducer were obtained from each square wave, overlayed and averaged to improve the signal-to-noise ratio before, during and 2 min following the work rate perturbation. All subjects had Doppler indices showing diastolic dysfunction (E:A <1.0 + IVRT >0.1 s) and all subjects achieved goal blood pressure by 4 weeks at 240 mg. Following 16 weeks treatment, resting LVDF was significantly improved: E:A 1.13 (0.4) and IVRT 0.08 (0.05) with no significant change in LVM. During loadless pedaling, E:A increased from 0.72 to 1.6 (p = 0.001), IVRT decreased from 0.13 to 0.08 s (p < 0.001) while VO₂ was unchanged. During cycling at 70% T_VT, E:A was increased from 0.66 to 2.0 (p < 0.001), IVRT was decreased from 0.17 to 0.05 s (p < 0.001) while VO₂ was unchanged. During the on-transient of exercise, E:A was increased from 0.72 to 1.0 (p < 0.01) and IVRT was decreased from 0.18 to 0.06 s (p < 0.001) while τ VO₂ was reduced from 67.3 to 38.7 s (p < 0.001). VO_2max was also increased from 22.3 to 24.1 ml/kg/min (p < 0.05). We conclude that improvement in resting and below T_VT diastolic filling and VO₂ kinetics with verapamil supports LVDF as a determinant of exercise response in these patients.

Diastolic filling, elderly, exercise performance