Original ArticleThe effect of continuous positive airway pressure therapy on arterial stiffness and endothelial function in obstructive sleep apnea: a randomized controlled trial in patients without cardiovascular disease
Introduction
Obstructive sleep apnea (OSA) is common and is caused by repetitive obstruction of the upper airway during sleep. When OSA leads to excessive daytime somnolence (EDS) it is termed obstructive sleep apnea–hypopnea syndrome (OSAHS), affecting 2–4% of the middle-aged population with an even greater proportion having evidence of OSA without EDS [1].
OSA is associated with increased cardiovascular morbidity and mortality [2], [3] and is an independent risk factor for hypertension [4]. Many mechanisms linking OSA and cardiovascular disease (CVD) have been proposed, with individual obstructive events associated with transient increases in blood pressure (BP) [5], arterial stiffness [6], and sympathetic activity [7]; all of which, along with systemic inflammation [8] and intrathoracic pressure swings, may contribute to endothelial dysfunction. We previously showed [9] that subjects with OSAHS in the absence of known CVD had evidence of increased arterial stiffness and impaired endothelial function when compared to well-matched control subjects.
Observational studies suggest that cardiovascular morbidity and mortality is lower in patients treated with continuous positive airway pressure (CPAP) therapy [2], [10], [11]. Randomized controlled trials (RCTs) have shown that CPAP therapy lowers BP [12], [13], and it also has been shown to improve endothelial function in small studies [14], [15]; however, many of these studies did not exclude patients with CVD [12], [13], [15]. To our knowledge, the effects of CPAP therapy on arterial stiffness had not yet been investigated prior to beginning our trial.
The aim of our double-blind, randomized, placebo-controlled, crossover trial was to examine the effects of CPAP therapy on arterial stiffness and endothelial function in subjects with OSA in the absence of overt CVD or diabetes mellitus (DM).
Section snippets
Subjects
Fifty-three subjects with OSA (apnea–hypopnea index [AHI] of ⩾15 on polysomnography), with no history of CVD or DM, were recruited through the Department of Sleep Medicine, Royal Infirmary of Edinburgh (Fig. 1). Exclusion criteria were previous CPAP therapy, respiratory failure, medications affecting BP, sleepiness when driving, professional driving, contraindications to magnetic resonance imaging, and intercurrent illness. EDS was defined as a score of ⩾11 on the Epworth Sleepiness Scale
Baseline characteristics and vascular measurements
Fifty-three subjects with OSA underwent baseline vascular assessments, of whom 10 did not complete the RCT (Fig. 1); baseline data for these subjects did not significantly differ from the 43 patients who completed the study. Baseline characteristics for those completing the study are shown in Table 1. The median AHI was 31, suggesting moderate disease severity; however, the mean minimum oxygen saturations were relatively high and the mean percentage of sleep time spent with oxygen saturations
Discussion
In a rigorous, double-blind, randomized, placebo-controlled, crossover trial, CPAP therapy lowered SBP with a trend towards a reduction in AIx after 12 weeks. However, CPAP therapy had no effect on PWV, AoD, or endothelial function in this group of subjects without CVD after 12 weeks.
OSA is associated with increased cardiovascular morbidity and mortality [2], [3], and numerous mechanisms are proposed. Using the same measures, we previously showed [9] that subjects with OSA and EDS had increased
Conclusions
In this group of subjects with relatively mild OSA in the absence of CVD or DM and in the context of a rigorous, double-blind, randomized, placebo-controlled crossover trial, we found that CPAP therapy lowered BP but had a nonsignificant effect on arterial stiffness, as measured by AIx, and did not modify endothelial function. Although it is clear that CPAP therapy is an effective treatment for EDS, more evidence is required, especially in patients with less severe OSA who do not have evidence
Funding sources
This study was funded by a British Heart Foundation project grant (PG/06/092/21267). We thank Dr. Tom Mackay and all of the staff within the Department of Sleep Medicine, the Department of Radiology and the Clinical Research Facility at the Royal Infirmary of Edinburgh.
Conflict of interest
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2013.08.786.
References (38)
- et al.
Long-term cardiovascular outcomes in men with obstructive sleep apnoea–hypopnoea with or without treatment with continuous positive airway pressure: an observational study
Lancet
(2005) - et al.
Arterial stiffness and endothelial function in obstructive sleep apnoea/hypopnoea syndrome
Sleep Med
(2013) - et al.
Ambulatory blood pressure after therapeutic and subtherapeutic nasal continuous positive airway pressure for obstructive sleep apnoea: a randomised parallel trial
Lancet
(2002) - et al.
Atherosclerosis and arterial stiffness in obstructive sleep apnea – a cardiovascular magnetic resonance study
Atherosclerosis
(2012) - et al.
Effect of continuous positive airway pressure treatment on daytime function in sleep apnoea/hypopnoea syndrome
Lancet
(1994) - et al.
The occurrence of sleep-disordered breathing among middle-aged adults
N Engl J Med
(1993) - et al.
Sleep-disordered breathing and cardiovascular disease: cross-sectional results of the Sleep Heart Health Study
Am J Respir Crit Care Med
(2001) - et al.
Sleep apnoea and hypertension: proof at last?
Thorax
(2001) - et al.
Arterial blood pressure responses to graded transient arousal from sleep in normal humans
J Appl Physiol
(1993) - et al.
Arterial stiffness increases during obstructive sleep apneas
Sleep
(2002)