Activity with ambulation attenuates diuretic responsiveness in chronic heart failure.

INTRODUCTION

We hypothesized that discharged heart failure (HF) patients could develop clinical congestion despite adhering to prescribed diuretics, because ambulation attenuates diuretic and natriuretic responsiveness.

METHODS

We studied 9 patients aged 57 ± 13 (mean ± SD) years with New York Heart Association functional class II-III symptoms and ejection fraction <40% (28 ± 7%) and receiving furosemide (≥80 mg/d [113 ± 53 mg/d]) plus renin-angiotensin system antagonists and beta-blockade. Inulin and p-amminohippuric acid were infused to estimate glomerular filtration rate (GFR) and renal plasma flow (RPF). Furosemide was administered intravenously at 75% of the usual oral morning dose. Participants were randomized to supine (90 minutes recumbancy) or upright (90 minutes sitting and treadmill walking) posture and assumed the other position on their second day. Primary outcome variables were urine volume and sodium excretion 90 minutes after furosemide.

RESULTS

On the upright, compared with the supine, day, urine volume (792 ± 484 vs 1,290 ± 503 mL; P = .02) and sodium (79 ± 55 vs 141 ± 61 mmol; P < .01) were attenuated, whereas plasma norepinephrine (4.4 ± 2.7 vs 2.3 ± 1.8 mmol/L; P = .01) and renin (327 ± 250% of supine; P < .01) were augmented. Urinary K+, mean pressure, GFR, and RPF were similar.

CONCLUSIONS

Activation of the sympathetic nervous system and renin-angiotensin axis by upright ambulation may attenuate diuresis and natriuresis by increasing proximal tubular reabsorption of sodium and water.