Figure 1. Distribution of the effects of nitric oxide inhalation on arterial oxygen tension (PaO2). Consistently positive tests (+) are defined as an increase > 10% in PaO2from baseline in repeated tests (blackened square); consistently negative tests (-) indicate lesser or no improvement (square). Patients with inconsistent responses (shaded square, +/-) had variably positive or negative test results. The number of patients (%) and the number of tests performed for each group of patients are shown inside the pieces of the pie.