Renal function in patients with chronic hypoxaemia and cor pulmonale following reversal of polycythaemia

The renal function of 7 patients with cor pulmonale and secondary polycythaemia was studied by clearance methods. Their haematocrit (Hct) was initially 62 +/- 6% (mean +/- SD). Their effective renal plasma flow rates (RPF) were reduced and filtration fractions (FF) increased. They were restudied 5-7 days after Hct reduction to 49 +/- 5%. There were no significant changes in glomerular filtration rate (GFR), RPF, FF, effective renal blood flow (RBF) or body weight. However, 5 of 7 patients had a reduction in FF and a fall in body weight. Serial measurements in one patient demonstrated that immediately following the reduction in Hct there was an increase in RPF and a fall in FF, but these reverted to previous levels within 1 week. Overall, a positive correlation was obtained between changes in body weight and FF (r = 0.85, n = 7, p less than 0.015). Polycythaemia is only one factor contributing to a low RPF and high FF in patients with cor pulmonale; reduction of the Hct reduces the FF in some patients and leads to a diuresis which may be beneficial in those with fluid retention.