Plasma levels of atrial natriuretic peptide and brain natriuretic peptide following intravenous saline infusion in oedematous chronic obstructive pulmonary disease and non-oedematous chronic obstructive pulmonary disease

Some patients with chronic obstructive pulmonary disease (COPD) develop oedematous COPD (oCOPD) with peripheral oedema and have a poor prognosis. The cause of the fluid retention is poorly understood but could be due to defective release of a natriuretic factor. We investigated this hypothesis by measuring levels of brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP) before and after a 0.1 ml/kg/min 2.7% saline infusion in 6 patients with hypoxemic COPD but no history of oedema and 7 COPD patients with oCOPD. Vasopressin, aldosterone, plasma and urinary urea and electrolytes and osmolality were measured. Arterial blood gases and spirometry were also recorded. The two groups were similar in terms of age, weight, PaO2, PaCO2 and FVC. FEV1 was significantly lower in the oCOPD group. The oCOPD group excreted less urine (202 +/- 23 vs. 364 +/- 48 ml; p < 0.05) and less sodium (32 +/- 3 vs. 68 +/- 9 mmol/l; p < 0.01) as a percentage of the saline load given (18 +/- 2 vs. 30 +/- 4%; p < 0.05). Pre-infusion BNP and ANP levels were similar in both groups. BNP and ANP had an exaggerated increase in the oCOPD group on saline loading. In the oCOPD group, ANP levels were significantly greater 1 h after the saline load compared to the pre-infusion values (30 +/- 7 vs. 11 +/- 2; p < 0.05). BNP did not reach significantly greater levels than baseline values until 3 h after the infusion had ended (45 +/- 6 vs. 27 +/- 2; p < 0.05). At 1 h after the saline load, BNP and ANP levels were significantly greater in the oCOPD group (BNP 32 +/- 2 vs. 24 +/- 1; p < 0.01 and ANP 30 +/- 7 vs. 7 +/- 2; p < 0.05) when compared to COPD controls. BNP levels remained significantly different from the COPD control group 3 h after the infusion ended (45 +/- 6 vs. 26 +/- 2; p < 0.05). Although aldosterone levels were greater in the oCOPD group before the saline infusion, the hormone level was suppressed appropriately by the infusion. In conclusion, the cause of oedema in oCOPD and the inability to excrete a saline load is not due to a failure of release of BNP or ANP.