PDE5A and chronic obstructive pulmonary disease: Remarkably, while studies have been reported on the long-term effects in the pediatric population with PH [6–9], evidence for similar long-term beneficial effects of PDE5 inhibitors in COPD patients is still controversial [10–12], thereby justifying experimental studies aiming to answer the question whether the effects of hypoxia, and hence of PDE5 inhibition, are time-dependent.