Fig. 4
Difference maps of the perfusion-height distribution visualizing the changes in mean normalized perfusion vs. height in response to the administration of O2 + iNO in PAH subjects and controls. Note that all subjects had regional responses to breathing O2 + iNO, including PAH subjects who had no discernible change in mean pulmonary arterial pressures with vasodilator challenge during cardiac catheterization. In controls, the changes in perfusion show a substantial spatial heterogeneity with an overall trend towards an increased vertical gradient during O2 + iNO and more uniform perfusion in the dependent (dorsal) regions (see also Fig. 2). In contrast, there are substantial changes in regional perfusion in PAH but not associated with a shift in the vertical gradient except for the confirmed responder among the PAH subjects shown in the second row. All panels use the same scale greyscale for the magnitude of differences