Fig. 9:  This Figure shows the effects of long-term supplemental oxygen therapy compared to controls who received no oxygen therapy.  As shown on the left, there was a reduction or stabilization of pulmonary artery pressures (Ppa) in the trial group compared to a rise in Ppa in the patients who did not receive oxygen at all.^[2]  The right panel shows results from the study from Timms et al^[4] that was part of the NOTT study and showed that patients who received continuous oxygen therapy at rest had a reduction in Ppa over time.  In addition, looking at exercise, there was a further reduction in Ppa with exercise, suggesting that continuous oxygen therapy had reduced Ppa levels at rest and with exercise, thus extending the findings of the MRC trial. 

Thus in aggregate these studies showed that long-term oxygen therapy could improve or reduce pulmonary artery pressures (Ppa) and treat secondary pulmonary hypertension in patients with hypoxemic COPD.