Pathogenesis of edema in constrictive pericarditis: Studies of body water and sodium, renal function, hemodynamics, and plasma hormones before and after pericardiectomy

Background. The pathogenesis of sodium and water accumulation in chronic constructive pericarditis is not well understood and may differ from that in patients with chronic congestive heart failure due to myocardial disease. This study was undertaken to investigate some of the mechanisms. Methods and Results. Using standard techniques, the hemodynamics, water and electrolyte spaces, renal function, and plasma concentrations of hormones were measured in 16 patients with untreated constrictive pericarditis and were measured again in eight patients after pericardiectomy. The average hemodynamic measurements were as follows: cardiac output, 1.98 l/min/m²; right atrial pressure, 22.9 mm Hg; pulmonary wedge pressure, 24.2 mm Hg; and mean pulmonary artery pressure 30.2 mm Hg. The systemic and pulmonary vascular resis-tances (36.3±2.5 and 3.2±0.3 mm Hg·min·m²/l, respectively) were increased. Significant increases occurred in total body water (36%), extracellular volume (81%), plasma volume (53%), and exchangeable sodium (63%). The renal plasma flow was only moderately decreased (49%), and the glomerular filtration rate was normal. Significant increases also occurred in plasma concentrations of norepinephrine (3.6 times normal), renin activity (7.2 times normal), aldosterone (3.4 times normal), cortisol (1.4 times normal), growth hormone (21.8 times normal), and atrial natriuretic peptide (5 times normal). The ratio of left atrial to aortic diameter measured by echocardiography was only minimally increased (1.29±0.04), indicating that in constrictive pericarditis the atria are prevented from expanding. The studies repeated after pericardiectomy in the eight patients showed that all measurements returned toward normal. Conclusions. The restricted distensibility of the atria, in constrictive pericarditis, limits the secretion of atrial natriuretic factor and, thus, reduces its natriuretic and diuretic effects. This results in retention of water and sodium greater than that occurring in patients with edema from myocardial disease. The arterial pressure is maintained more by the expansion of the blood volume than by an increase in the peripheral vascular resistance.