Effects of Body Position on the Carbon Monoxide Diffusing Capacity in Patients with Chronic Heart Failure: Relation to Hemodynamic Changes

Abstract

Objective: Pulmonary diffusion has been found to be reduced in patients with congestive heart failure. The effects of postural changes on the diffusing capacity had been evaluated in healthy subjects, but not in patients with heart failure. The aim of this study was to evaluate the posture-induced changes in diffusing capacity in patients with chronic heart failure and their relation to the hemodynamic profile. Methods: The pulmonary carbon monoxide diffusing capacity (DLCO) was measured in the supine position, with 20° passive head elevation, and in the sitting position, both postures maintained for 10 min, in a group of 32 male patients with mild to moderate chronic heart failure due to left ventricular systolic dysfunction (ejection fraction <35%). On a separate day, in the absence of any changes in clinical status and therapy, the hemodynamic parameters were measured by right-heart catheterization. The sequence of postures was assigned randomly. Results: The mean values of DLCO were slightly reduced and did not differ in the two positions (20.3 ± 5.7 vs. 19.4 ± 5.6 ml/min/mm Hg, 77 ± 23 vs. 75 ± 20% of predicted, respectively). The patients were then subdivided according to changes in DLCO from the supine to the sitting position: DLCO increased (+23%) in 9 patients (28%, group 1), decreased (–17.5%) in 17 patients (53%, group 2), and remained within the coefficient of reproducibility (±5%) in 6 patients (group 3). As compared with group 2, group 1 patients showed a significant increase in mean pulmonary artery pressure (+7 vs. –15%, p < 0.01) and pulmonary capillary wedge pressure (+8 vs. –22%, p < 0.005) from the supine to the sitting position, while the cardiac index showed a smaller – but not significant – decrease in group 1 (–5 vs. –12%). The percent changes in DLCO significantly correlated with changes in pulmonary capillary wedge (r = 0.54, p < 0.0005) and mean pulmonary artery (r = 0.47, p < 0.005) pressures. Conclusions: In chronic heart failure postural changes may induce different responses in diffusing capacity. To a greater extent than in healthy subjects, the most common response is a decrease in DLCO in the sitting as compared with the supine position. The DLCO changes correlate with variations in pulmonary circulation pressure, probably due to changes in pulmonary vascular recruitment and pulmonary capillary blood volume.