"Effect of CPAP on Blood Pressure in Patients With Obstructive Sleep Apnea and Resistant Hypertension The HIPARCO Randomized Clinical Trial'
JAMA
http://jama.jamanetwork.com/article.aspx?articleid=1788459 
"Conclusions and Relevance  Among patients with OSA and resistant hypertension, CPAP treatment for 12 weeks compared with control resulted in a decrease in 24-hour mean and diastolic blood pressure and an improvement in the nocturnal blood pressure pattern. Further research is warranted to assess longer-term health outcomes."