Table 1.

Enumerates the limitations of randomized control studies which have investigated the impact of PAP therapy on cardiovascular diseases in OSA [67].

Selection bias	Samples selected were not reflective of the population. Trials recruited patients with established cardiovascular disease and hence were aimed at secondary prevention. Excluded patients with greatest risk of cardiovascular disease, such as patients with “symptomatic sleepiness” due to ethical concerns, hence likely impacting the outcome of the study.
Adherence to PAP therapy was sub optimal.	Patients recruited had established cardiovascular disease and did not present with OSA initially. Hence, adherence to PAP therapy was sub-optimal and invariably less than 4 h/night and hence may have impacted the results of the clinical trials.
Lack of adequate numbers and hence void of statistical power to show difference in outcome	The clinical trials were small in number and lacked statistical power. All the studies had this limitation.
“Composite end point” as outcome was a limitation	The studies chose “Composite end point” as the outcome which consisted of various competing events such as stroke, myocardial infarction, heart failure, angina, etc., which were not equal in terms of weightage. Small sample size, inadequate power and smaller number of individual events altogether impacted the final outcome.

OSA: obstructive sleep apnea; PAP: positive airway pressure.