Impact of acute reduction in chronically elevated left atrial pressure on sodium and water excretion

To test the hypothesis that a reduction in chronically elevated left atrial pressure would decrease sodium and water excretion in humans, we studied 61 carefully selected patients who underwent cardiac surgery for valvular or coronary artery disease or both. The immediate postoperative decrease in left atrial pressure (from 16.7 +/- 1.0 to 9.4 +/- 0.4 mm Hg; p less than 0.001) was inversely correlated with postoperative urine output (r = -0.69; p less than 0.001) and sodium excretion (r = -0.51; p less than 0.005). There was no significant relationship between postoperative urine output or sodium excretion and other hemodynamic or nonhemodynamic variables. A significant postoperative decrease in plasma atrial natriuretic factor (from 150 +/- 22 to 65 +/- 14 pg/ml; p less than 0.01) and increase in plasma renin activity (from 2.5 +/- 0.6 to 8.7 +/- 3.2; p less than 0.05) occurred in patients with a 7 mm Hg or greater postoperative decrease in left atrial pressure. Thus, an acute reduction in left atrial pressure results in significant reductions in urine output and sodium excretion, the magnitude of which are related to the degree of reduction in left atrial pressure.