Does long-term oxygen therapy cause surfactant deficiency?

It depends.... ...On oxygen concentration and degree of exposure. There is no question that 100% oxygen can damage surfactant. But, I doubt whether usual nasal o2 of 1-2 li/min will. The less frequent one uses o2 rx, the safer it is for surfactant. However, there maybe other reasons for surfactant deficiency.
No. Only high concentrations of oxygen, above 70%, for an extended period of time, measured in days, will cause long term pulmonary injury. Routine medical oxygen therapy, such as that for copd, is highly unlikely to influence surfactant.