According to a study, researchers determined that supplemental oxygen significantly reduces morning blood pressure in patients with obstructive sleep apnea (OSA). OSA is associated with elevated daytime blood pressure, and CPAP has been shown to improve blood pressure, particularly in patients with resistant hypertension.
Whether CPAP works by abolishing intermittent hypoxia or reducing arousals remains unclear. The study was published in the journal American Journal of Respiratory and Critical Care Medicine,
Researchers sought to clarify whether intermittent hypoxia is important in daytime pressure elevations in OSA in their trial of 25 patients with moderate-to-severe OSA who had been treated with continuous positive airway pressure (CPAP) for at least one year.
Patients were randomized at visit 1 to receive overnight supplemental oxygen or air at a rate of 5 l/min via either nasal cannulae or fitted face mask, instead of their CPAP for 2 weeks. Following that, after a 2-week washout period back on CPAP, at visit 3, patients crossed over to receive supplemental air or oxygen for another 2 weeks, again instead of their CPAP.
Supplemental oxygen abolished the rise in home blood pressure seen with supplemental room air, with a relative decrease of 6.6 mm Hg systolic and 4.6 mm Hg diastolic blood pressure. Supplemental oxygen had no significant effect on home or office morning heart rate, compared with room air.
Episodes of oxygen desaturation >4% declined a median 23.8 per hour with supplemental oxygen, compared with room air, and the percentage time with oxygen saturation <90% declined by a median 9.8%.
Daytime sleepiness, overnight urinary volume, and creatinine concentration, and overnight urinary sympathetic biomarkers did not differ significantly between the supplemental oxygen and room air periods.
Whilst the exact mechanisms underlying the attenuation of blood pressure rises by oxygen during CPAP withdrawal are not clear, intermittent hypoxia, and not arousal-mediated sympathetic activation, appears to be the likely dominant cause of daytime increases in blood pressure in OSA.
This was a physiological mechanistic study and future research is needed to see if this translates into a potential clinical benefit. Previous trials assessing supplemental oxygen in OSA excluded patients with the most severe hypoxia, and this is probably the group most likely to benefit from oxygen treatment.
CPAP has a greater effect on blood pressure in patients with resistant hypertension. Thus, the effect of supplemental oxygen on blood pressure should be assessed in patients with OSA and resistant hypertension, with significant nocturnal intermittent hypoxia, where CPAP is not indicated or tolerated, but with careful monitoring of carbon dioxide levels.