Repetitive Hemodilution in Chronic Obstructive Pulmonary Disease and Pulmonary Hypertension: Effects on Pulmonary Hemodynamics, Gas Exchange, and Exercise Capacity

Abstract

BACKGROUND: In cor pulmonale associated with severe chronic obstructive pulmonary disease (COPD), disturbances of pulmonary microcirculation may contribute significantly to hypoxemia, pulmonary hypertension, and exercise intolerance. OBJECTIVE: It was tested whether reduction of blood viscosity induced by repetitive hemodilution might improve pulmonary hemodynamics and oxygen uptake. METHODS: Seven patients with stable COPD (forced expiratory volume in 1 s 33 +/- 3 % of predicted, means +/- SE) and pulmonary hypertension were phlebotomized 5-6 times over a period of 3 months with substitution of 6% hydroxyethyl starch (molecular weight 40, 000). This resulted in a stepwise reduction of the hematocrit from 53.3 +/- 2.6 to 45.8 +/- 3.1% and a reduction of whole blood viscosity from 9.8 +/- 0.6 to 8.8 +/- 0.7 mPa x s at a shear rate of 2.0 s-1. Before and after the treatment period, patients underwent cardiopulmonary exercise testing and right heart catheterization. RESULTS: Mean pulmonary artery pressure (PAm) decreased from 30 +/- 3 to 22 +/- 2 mm Hg and arterial oxygen partial pressure (PaO2) increased from 63.2 +/- 2.2 to 71.8 +/- 3.7 mm Hg at rest. During peak exercise, PAm decreased from 59 +/- 7 to 53 +/- 7 mm Hg and PaO2 increased from 54.0 +/- 5.7 to 63.2 +/- 2.4 mm Hg after hemodilution. Peak oxygen consumption rose from 573 +/- 84 to 750 +/- 59 ml x min-1, corresponding to an increase in cardiac index from 4.25 +/- 0.5 to 5.88 +/- 0.76 liters x min-1 x m-2. Pulmonary vascular resistance fell from 345 +/- 53 to 194 +/- 32 dyn x s x cm-5. The patients' peak exercise capacity increased from 9.2 +/- 2. 0 before to 13.5 +/- 3.2 kJ at the end of the study (p < 0.05 for all differences, paired t test). CONCLUSION: The findings suggest that a prolonged improvement of pulmonary microcirculation by reducing blood viscosity may improve pulmonary gas exchange, central hemodynamics, and exercise tolerance in patients with severe COPD and pulmonary hypertension.