Figure 4. Dose-response experiment. Perfusion of the hypoxic lobe as a percentage of cardiac output. At baseline (BL), inspired fraction of oxygen is 0.8 to both lungs, at nitric oxide (NO) concentrations of 0 ppm and greater it is 0.05 to LLL and 0.8 to the other lung regions. Nitric oxide was delivered to the hypoxic lobe in increasing doses, and there was an increase in blood flow with concentrations to 40 ppm. With greater concentrations there was only a minor increase in the perfusion of the hypoxic lobe. Comparisons were performed with analysis of variance for repeated measurements and Fisher's test of least significant difference, #P < 0.05 and ##P < 0.01 compared with baseline;*P < 0.05 and **P < 0.01 compared with 0 ppm; and multipointed star P < 0.05 and double multipointed star P < 0.01 compared with 5 ppm.