The effects of hypoxia and hypercapnia on renal and heart function, haemodynamics and plasma hormone levels in stable COPD patients

Background: Fluid retention with oedema is an important clinical problem in advanced chronic obstructive pulmonary disease (COPD). Objective: The aim of this study was to investigate cardiovascular, hormonal, renal and pulmonary function data and their possible relation to fluid retention in COPD. Methods: The study group consisted of 25 stable outpatients with COPD. The presence of oedema was assessed by clinical examination and the intake of diuretics was recorded. Glomerular filtration rate (GFR) and the renal blood flow (RBF) were measured. Lung function was assessed with standard spirometry. Cardiac function and haemodynamic variables were studied using echocardiography and equilibrium radionucleotide angiography. The plasma levels of noradrenaline, plasma renin activity, angiotensin II, aldosterone, atrial natriuretic peptide, brain natriuretic peptide and antidiuretic hormone were measured. Results: Systolic and diastolic cardiac functions were found to be well preserved in the patients. Hypercapnia and impaired lung function, but not hypoxia, were clearly associated with oedema/intake of diuretics, low diuresis, low GFR, low RBF and high renal vascular resistance. These effects had no significant relationship to central haemodynamics or the measured plasma hormone levels. Conclusions: In stable COPD, renal fluid retention and oedema are enhanced by hypercapnia-induced renal vasoconstriction and antidiuresis. In contrast to some earlier reports, this effect does not seem to be mediated via the central haemodynamic reflex systems or the measured plasma hormones. In addition, hypoxia had no significant effect on fluid retention in this group of patients.