Diffusing Capacity for Nitric Oxide and Carbon Monoxide in Patients With Diffuse Parenchymal Lung Disease and Pulmonary Arterial Hypertension: Dlno Measurement
All patients with suspected PAH underwent radionuclide perfusion and ventilation scans, echocardiography with estimation of the pulmonary artery pressure by tricuspid regurgitation measurement (assessed by experienced cardiologists), CT scan of the pulmonary arteries in order to detect central thromboembolic disease, right heart catheterization with measurements of the pulmonary artery pressure with reversibility testing in most patients (epoprostenol), and pulmonary angiography when indicated. Consultation by rheumatologists included the performance of serum immunologic tests in search of collagen vascular disease and scleroderma. A definite diagnosis of PAH was made based on the Revised Clinical Classification of Pulmonary Hypertension. further
A combined single-breath Dlno and Dlco measurement was performed on an adapted instrument (MasterLab Pro; Erich Jaeger GmbH). The test gas contained a mixture of CO 0.25%, He 9.17%, and NO 8 ppm with balance air. The NO was added to the test gas directly before each measurement from a separate tank containing 750 ppm NO in nitrogen (Hoekloos Medical; Schiedam the Netherlands). The singlebreath procedure was performed according to American Thoracic Society recommendations11 with an effective breathhold-ing period of 10 s (the Jones and Meade method), a discard volume of 750 mL, and a sample volume of 750 mL. The device (MasterLab Pro; Erich Jaeger GmbH) sampled the He and CO concentration in the expired air, and a chemolumi-nescence analyzer (CLD 77 am; Eco Physics; Zurich, Switzerland [lower detection limit, 0.02 to 0.05 parts per billion (ppb); upper detection limit, 10 ppm; reaction time 0.1 s]) measured the NO concentration. Once a week, the chemoluminescence analyzer was calibrated with 5 ppm NO in nitrogen and NO-free air. All connections between the NO analyzer and the inspiratory and expiratory bags were made of polytetrafluoro-ethylene (Teflon; DuPont; Wilmington, DE) or stainless steel, which do not interact with NO. The alveolar volume (VA) and Dlco were calculated according to European Respiratory Society recommendations, and the Dlno was calculated according to the method described by Borland and Higenbot-tam, which is the same formula for using NO concentrations instead of CO concentrations. Endogenous NO levels and CO backpressure were ignored, and smoking was allowed until 24 h before testing.