Elsevier

Sleep Medicine

Volume 3, Issue 4, July 2002, Pages 329-334
Sleep Medicine

Original article
Dose–response relationship between CPAP compliance and measures of sleep apnea severity

https://doi.org/10.1016/S1389-9457(02)00010-2Get rights and content

Abstract

Background: Obstructive sleep apnea is a prevalent condition with serious medical and psychosocial consequences. Nasal continuous positive airway pressure (CPAP) is the treatment of choice and has been shown to reduce the frequency of nocturnal respiratory events, improve sleep architecture, and decrease daytime sleepiness. However, little is known about the dose–response relationship between CPAP compliance and measures of sleep apnea severity. This study examined the relationship between level of CPAP compliance and change in polysomnographic measures of sleep apnea severity.

Methods: Twenty-three CPAP-naive OSA patients were studied. None had other major medical illnesses or were receiving antihypertensive medication. Sleep apnea variables were measured at baseline and after 1 week of treatment. Objective CPAP compliance was measured nightly and was defined as the average number of hours of use per night.

Results: Higher rates of CPAP compliance were linearly associated with significant reductions in the respiratory disturbance index (R=0.49, P=0.017), the oxygen desaturation index (R=0.48, P=0.029), and the arousal index (R=0.51, P=0.016).

Conclusions: These data suggest that increased CPAP compliance is linearly associated with reductions in sleep apnea severity such that greater reductions in apnea were seen with increased CPAP use. It should be noted that all patients were reasonably compliant (i.e. >4 h CPAP use/night) and that even within this range of reasonable compliance, there was a significant benefit with more as opposed to less compliance. These findings offer support to the current recommendation that CPAP be used during the total time in bed to optimize treatment of polysomnographic measures of sleep apnea.

Introduction

Obstructive sleep apnea (OSA) is a disorder characterized by repeated complete cessations and/or reductions of breathing during sleep [1]. The clinical effectiveness of CPAP [2] in treating OSA is well documented. Continuous positive airway pressure (CPAP) has been shown to reduce daytime sleepiness [3], reduce oxyhemoglobin desaturations [4], reduce heart rate and pulmonary pressure [5], improve cognitive performance [6], and increase health-related quality of life [7]. In addition, compliance with CPAP treatment has been shown to result in a significant reduction in physician claims and hospital stays [8].

The heart of any CPAP prescription is a titration pressure by time exposure. This matter of ‘time’ is problematic because: (a) so few patients use CPAP religiously all the night through, and (b) the literature is unclear about whether the benefits from CPAP exposure are linear or whether they occur only after a certain threshold number of hours. Unfortunately, compliance with CPAP is poor to the extent that any use greater than 4 h per night is operationally defined as ‘good’ compliance [9]. We wondered if the benefit of CPAP would be evident even without the admittedly restricted range of ‘good compliance’.

Despite the multitude of studies done to date, relatively little is known about the dose–response relationship between CPAP compliance and sleep apnea severity, and consequently the minimum threshold compliance level for improving outcomes has not been established. The current recommendation is for patients to use CPAP continuously while asleep, including naps [10], [11]. The recommendation is based on full and partial night CPAP withdrawal studies that have examined the effects of CPAP discontinuation. However, the withdrawal studies that have been performed to date have shown mixed results (see Table 1). Following 2–3 months of treatment, patients off of CPAP for 1 night had a significant worsening of apnea severity and daytime sleepiness [3]. Similarly, a study with a 1-year treatment period found that apnea severity and daytime sleepiness worsened after 1 night off of CPAP [12]. In contrast, no change in apnea level was seen following 1 night without CPAP after treatment for 6 weeks [13]. More recently, using a split-night procedure, Hers and coworkers found that reduced apnea levels did not change when subjects crossed-over from CPAP in the first half of the night to none on the second half [14]. The authors suggest that a carry over effect occurs that may explain why a large number of OSA patients apply CPAP for only part of the night or not every night.

Another way of investigating the dose–response relationship between CPAP compliance and sleep apnea severity is to examine the relationship between the change in sleep apnea and compliance level over a defined period of time. To our knowledge, only one randomized, controlled CPAP trial to date has reported on the relationship between compliance and measures of sleep apnea severity. In a sample of patients with mild sleep apnea, defined by a respiratory disturbance index (RDI) between 5 and 15, Engleman and coworkers found that higher compliance was associated with higher initial RDI and microarousal indices [15]. Though the authors speculate that those patients with more symptoms may use the machine to a greater extent, the implications of this study are unclear for those with moderate to severe sleep apnea.

The current study reports on the effect of CPAP compliance on sleep apnea severity in a sample of patients with moderate to severe sleep apnea. We previously reported that CPAP was effective in lowering the RDI and the number of arousals, and in raising the sleep arterial oxygen saturation (SaO2), relative to a placebo group [16]. The purpose of this paper is to expand on those findings by examining the relationship between CPAP compliance and measures of sleep apnea severity. It was hypothesized that increased CPAP compliance would be linearly associated with greater reductions in sleep apnea severity, e.g. lower RDI, fewer arousals, and improved nocturnal oxygen saturation levels.

Section snippets

Participants

Twenty-three CPAP naive OSA subjects were studied at the University of California, San Diego (UCSD) Clinical Research Center (CRC). They ranged in age from 32 to 60 years and their weight was between 1.0 and 1.7 times ideal body weight (see Table 2). Subjects were excluded if they were receiving medications known to affect their sleep or if they had congestive heart failure, symptomatic obstructive pulmonary, coronary, or cerebrovascular disease, history of life-threatening arrhythmias,

Results

Our patient sample was composed of moderately obese individuals with moderate to severe sleep apnea. Table 2 shows the sample characteristics. Each subject was successfully titrated to an RDI <5. All patients complied well during the 1-week of treatment, with every CPAP utilization ranging from 4.4 to 7.7 h per night. We then calculated the relationship between these varying amounts of good compliance with respiratory disturbance index (RDI), ARI, and ODI.

Discussion

No studies from randomized, controlled clinical trials of moderate to severe CPAP have reported on the relationship between CPAP compliance and measures of apnea severity. The results from this study have shown that higher rates of CPAP compliance were linearly associated with significant reductions in the number of respiratory disturbances per hour of sleep, the number of oxygen desaturations per hour of sleep, and the number of arousals per hour of sleep. These data offer preliminary support

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