Abstract 4005: Activity With Ambulation Influences Diuretic Responsiveness in Chronic Heart Failure
Introduction: Many hospitalized heart failure (HF) patients are readmitted with return of congestion despite compliance with their diuretic dose on discharge. However, the latter is often established when patients are predominantly supine. We hypothesized that increased ambulation post-discharge might render patients relatively more diuretic resistant.
Methods: We studied twice 9 patients (7 men) with an average age of 57±13 (mean±s.d) years with NYHA Class II–III symptoms, left ventricular ejection fraction (LVEF) <40% (mean 28%±7 ), and stable (unchanged >4 weeks) furosemide dose ≥80mg/day (mean 113 mg±53 ). All were receiving ACEi or ARBs plus beta-blockade. On both days furosemide was administered i.v. at 75% of the usual a.m. oral dose. Inulin and p-amminohippuric acid were infused continuously to estimate glomerular filtration rate (GFR) and renal plasma flow (RPF). Patients then were randomized to be either supine (90 min recumbancy) or upright (90 min sitting and treadmill walking at a leisurely pace), and assumed the alternate posture on the second study day. BP was measured before, and 30, 60 and 90 min after furosemide, and venous blood drawn at 90 min. The primary outcome was urine volume and urine sodium excretion 90 min post-furosemide.
Results: Mean arterial pressure in upright and supine positions were 76.4±11.3 mmHg and 77.0±11.3 respectively (p=n.s.). Urine volume (1290±503 ml vs 792±484 ml, p=0.02) and urinary sodium excretion (141±61 mmol vs 79±55 mmol, p<0.01) were greater with patients supine, whereas norepinephrine (4.4±2.7 mmol/L vs 2.3±1.8 mmol/L, p=0.01) and relative renin (327±250% of supine; p<0.01) were greater with patients upright. Urinary K+ GFR, RPF, and atrial natiuretic peptide were similar on the 2 study days.
Conclusion: In chronic HF patients receiving contemporary drug therapy, urine sodium and volume excretion are attenuated by upright ambulation. This occurs independently of changes in MAP, RBF or GFR. Activation of the sympathetic nervous system and renin-angiotensin axis as a consequence of upright ambulation may attenuate diuresis by decreasing Na+ delivery to the distal tubule. These changes should be considered in the management of such patients.