INCREASED ALVEOLAR CAPILLARY MEMBRANE RESISTANCE TO GAS TRANSFER IN PATIENTS WITH CHRONIC HEART-FAILURE/

Objective-To investigate pulmonary diffusive resistance to gas exchang e in patients with heart failure and healthy volunteers, assessing the relative contributions of the alveolar/capillary membrane and pulmona ry capillary blood. Setting-Hospital outpatient department and pulmona ry function laboratory. Patients-38 patients (mean age 60) receiving t reatment with loop diuretics and angiotensin converting enzyme inhibit ors for stable symptomatic heart failure of > 6 months duration (New Y ork Heart Association (NYHA) classes II and III). Results were compare d with those of 17 healthy volunteers (mean age 52). Methods-The alveo lar/capillary membrane diffusive resistance and the pulmonary capillar y blood volume available for physiological gas exchange were determine d by the Roughton and Forster method, which measures the single breath pulmonary diffusing capacity for carbon monoxide at varying alveolar oxygen concentrations. Results-Total pulmonary diffusive resistance wa s higher in patients than controls. Alveolar/capillary membrane resist ance formed the main component of this increase, accounting for a mean (SD) of 63% (20%) and 86% (8%) of total pulmonary diffusive resistanc e in patients in NYHA II and III classes respectively, compared with 5 3% (10%) in controls. The pulmonary capillary blood volume was not sig nificantly different between controls and patients in NYHA class II (6 6 (18)ml upsilon 61 (18) ml), but was increased in those in NYHA class III (95(46) ml, P < 0.05). Conclusion-This study confirmed impairment of pulmonary diffusion at rest in patients with chronic heart failure and identified impaired alveolar/capillary membrane function as the m ain factor responsible.