To determine whether inhaled nitric oxide (NO) affects pulmonary circulation, thereby improving right ventricular (RV) function in adult respiratory distress syndrome (ARDS), we studied 13 patients with both a lung injury severity score of 2.5 or more and a mean pulmonary artery pressure higher than 30 mm Hg. RV function was assessed by a thermodilution technique using a pulmonary artery catheter equipped with a rapid response thermistor before and 15 min after initiation of inhalation of NO (5 ppm). At baseline, stroke volumes were in a normal range (46 +/- 14 ml/m2), with a RV dilation (end-diastolic volume = 142 +/- 36 ml/m2). Inhaled NO was followed by an improvement in arterial oxygenation (PaO2/FIO2 = 103 +/- 47 versus 142 +/- 63, p < 0.05) and a drop in pulmonary artery pressure (36.1 +/- 4.5 versus 31.3 +/- 6.1 mm Hg, p < 0.01); stroke volumes and heart rates did not change. The resulting fall in pulmonary vascular resistance (211 +/- 43 versus 180 +/- 59 dyn-s/cm5, p < 0.05) was associated with an increase in RV, ejection fractions (32 +/- 5 versus 36 +/- 6%, p < 0.05), a trend toward decreased RV end-systolic (96 +/- 25 versus 85 +/- 19 ml/m2, NS) and end-diastolic (142 +/- 36 versus 131 +/- 27 ml/m2, NS) volumes, and a decrease in right atrial pressures (10.9 +/- 2.9 versus 9.6 +/- 3.2 mm Hg, p < 0.05). No relationship was seen between the improvement in arterial oxygenation and the decrease in pulmonary vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)