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Randomized Controlled Trial
. 2019 Jan 15;199(2):211-219.
doi: 10.1164/rccm.201802-0240OC.

Effect of Supplemental Oxygen on Blood Pressure in Obstructive Sleep Apnea (SOX). A Randomized Continuous Positive Airway Pressure Withdrawal Trial

Chris D Turnbull  1   2 , Dushendree Sen  2 , Malcolm Kohler  3   4 , Nayia Petousi  5 , John R Stradling  1
Affiliations
Randomized Controlled Trial

Effect of Supplemental Oxygen on Blood Pressure in Obstructive Sleep Apnea (SOX). A Randomized Continuous Positive Airway Pressure Withdrawal Trial

Chris D Turnbull et al. Am J Respir Crit Care Med. .

Abstract

Rationale: Obstructive sleep apnea (OSA) is associated with systemic hypertension. Either overnight intermittent hypoxia, or the recurrent arousals that occur in OSA, could cause the daytime increases in blood pressure (BP).

Objectives: To establish the role of intermittent hypoxia in the increased morning BP in patients with OSA.

Methods: Randomized, double-blinded, crossover trial assessing the effects of overnight supplemental oxygen versus air (sham) on morning BP, after continuous positive airway pressure (CPAP) withdrawal in patients with moderate to severe OSA. The primary outcome was the change in home morning BP after CPAP withdrawal for 14 nights, oxygen versus air. Secondary outcomes included oxygen desaturation index (ODI), apnea-hypopnea index (AHI), subjective sleepiness (Epworth Sleepiness Scale score), and objective sleepiness (Oxford Sleep Resistance Test).

Measurements and main results: Supplemental oxygen virtually abolished the BP rise after CPAP withdrawal and, compared with air, significantly reduced the rise in mean systolic BP (-6.6 mm Hg; 95% confidence interval [CI], -11.3 to -1.9; P = 0.008), mean diastolic BP (-4.6 mm Hg; 95% CI, -7.8 to -1.5; P = 0.006), and median ODI (-23.8/h; interquartile range, -31.0 to -16.3; P < 0.001) after CPAP withdrawal. There was no significant difference, oxygen versus air, in AHI, subjective sleepiness, or objective sleepiness.

Conclusions: Supplemental oxygen virtually abolished the rise in morning BP during CPAP withdrawal. Supplemental oxygen substantially reduced intermittent hypoxia, but had a minimal effect on markers of arousal (including AHI), subjective sleepiness, or objective sleepiness. Therefore intermittent hypoxia, and not recurrent arousals, appears to be the dominant cause of daytime increases in BP in OSA.

Keywords: blood pressure; intermittent hypoxia; obstructive sleep apnea.

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Figures

Figure 1.
Figure 1.
SOX trial flow diagram. Patients initially underwent 1 week of overnight screening pulse oximetry. After screening, and after 14 days back on CPAP, patients were allocated either oxygen or air concentrators, with treatment order randomized. Between the two treatment arms patients had a washout period of at least 2 weeks back on CPAP. BP = blood pressure; CPAP = continuous positive airway pressure; SOX = Supplemental Oxygen during CPAP Withdrawal.
Figure 2.
Figure 2.
CONSORT diagram showing the flow of the 57 patients who entered screening and the 38 patients who were randomized in the SOX (Supplemental Oxygen during CPAP Withdrawal) trial. CONSORT = Consolidated Standards of Reporting Trials; CPAP = continuous positive airway pressure; ODI = oxygen desaturation index.
Figure 3.
Figure 3.
(A and B) Mean systolic (A) and diastolic (B) blood pressure in both treatment arms. Mean values are represented by circles (baseline) and diamonds (follow-up), and error bars represent the 95% confidence intervals (solid lines at baseline and dashed lines at 2-wk follow-up).
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