Can new pulmonary gas exchange parameters contribute to evaluation of pulmonary congestion in left-sided heart failure?

Background Assessment of pulmonary congestion in left-sided heart failure is necessary for guiding anticongestive therapy. Clinical examination and chest x-ray are semiquantitative methods with poor diagnostic accuracy and reproducibility. Objectives To establish reference values, describe reproducibility, and investigate the diagnostic and monitoring properties in relation to pulmonary congestion of new pulmonary gas exchange parameters describing ventilation/perfusion mismatch (variable fraction of ventilation [fA2] or the drop in oxygen pressure from the mixed alveolar air of the two ventilated compartments to the nonshunted end-capillary blood [ΔPO2 ]) and pulmonary shunt. Methods Sixty healthy volunteers and 69 patients requiring an acute chest x-ray in a cardiac care unit were included. The gas exchange parameters were estimated by analyzing standard bedside respiratory and circulatory measurements obtained during short-term exposure to different levels of inspired oxygen. Nine patients were classified as having pulmonary congestion using a reference diagnosis and were followed during 30 days of anticongestive therapy. Diagnostic and monitoring properties were compared with chest x-ray, N-terminal probrain natriuretic peptide (NT-proBNP), spirometry values, arterial oxygen tension, alveolar-arterial oxygen difference and venous admixture. Results The 95% reference intervals for healthy subjects were narrow (ie, fA2 [0.75 to 0.90], ΔPO2 [0.0 kPa to 0.5 kPa] and pulmonary shunt [0.0% to 8.2%]). Reproducibility was relatively good with small withinsubject coefficients of variation (ie, fA2 [0.05], ΔPO2 [0.4 kPa] and pulmonary shunt [2.0%]). fA2, ΔPO2 and NT-proBNP had significantly better diagnostic properties, with high sensitivities (100%) but low specificities (30% to 40%). During successful anticongestive therapy, fA2, ΔPO2 , NT-proBNP and spirometry values showed significant improvements. Conclusions The gas exchange parameter for ventilation/perfusion mismatch but not pulmonary shunt can have a possible role in rejecting the diagnosis of pulmonary congestion and in monitoring anticongestive therapy.