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* From the Departments of Pulmonary Medicine (Drs. Sin, Mayers, and Man, and Mr. Ghahary) and Psychiatry (Dr. Pawluk), University of Alberta, Edmonton, AB, Canada.
Correspondence to: Don D. Sin, MD, MPH, 2E4.29 Walter C. Mackenzie Center, University of Alberta, Edmonton, AB, Canada. T6G 2B7; e-mail: don.sin{at}ualberta.ca
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Abstract |
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 TOP Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Design: Prospective longitudinal cohort study.
Setting: University sleep disorders center.
Patients: Three hundred sixty-five patients
with an apnea-hypopnea index (AHI) 
20 per hour of sleep and 358
patients with an AHI of < 20.
Interventions: All
patients with AHIs 20 received CPAP therapy; those with AHIs < 20
did not. The HRQL of all study participants was measured using the
36-item medical outcomes study short form (SF-36) questionnaire at
baseline and then at 3 and 12 months of follow-up.
Results: Although the SF-36 scores were similar at
baseline, after 3 months of therapy, the CPAP group had higher adjusted
emotional summary scores than did those who did not receive CPAP
therapy (score increase, 1.72; 95% confidence interval [CI], 0.08 to
3.37). These improvements were maintained for 12 months. The gains in
the SF-36 scores were most striking in the vitality domain (score
increase, 10.52; 95% CI, 7.04 to 14.00 U increment). The severe OSA
group (ie, AHIs 40) experienced the largest benefit.
Their adjusted vitality scores were 12.3 U higher (95% CI, 8.0 to
16.6) than those persons without OSA (ie, AHIs
< 5).
Conclusions: CPAP therapy was associated with marked short-term and long-term improvements in the vitality of patients with moderate-to-severe OSA in the community. These findings suggest that CPAP therapy is effective in improving the long-term HRQL of patients with OSA.
Key Words: continuous positive airway pressure • health-related quality of life • obstructive sleep apnea • 36-item medical outcomes study short form questionnaire
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Since the early 1980s, continuous positive airway pressure (CPAP), applied through a nasal mask, has been the primary modality for the treatment of patients with OSA.5 Although it is not curative, CPAP therapy prevents upper airway collapse, leading to a more restful night of sleep.6 Multiple anecdotal reports, case-series, and prospective studies provide testimonials on the benefits of CPAP therapy in restoring normal sleep architecture and relieving daytime sleepiness.7 8 9 10 11 12 13 Several randomized controlled trials (RCTs)14 15 16 17 have demonstrated that over a short period of time CPAP relieves daytime sleepiness and improves the health-related quality of life (HRQL) of patients with OSA syndrome. However, as the RCTs have focused on short-term clinical end points,14 15 16 17 it is not known whether these early benefits of CPAP therapy are maintained over a longer period of time. We, therefore, conducted a clinical effectiveness study to determine the impact of CPAP therapy on both the short-term and long-term HRQL of patients with OSA in the community.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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20 per hour of
sleep were invited to receive CPAP therapy.18
Of the
patients who were eligible, none refused CPAP therapy. Patients with
AHIs of < 20 per hour were not offered CPAP therapy, except in cases
in which patients had a pathologic degree of daytime sleepiness and had
been judged by the treating physicians as suitable candidates for CPAP
therapy. Patients with AHIs of < 20 who received CPAP therapy were
excluded from the study. The remaining patients were classified into
the following four major categories: no OSA (AHI < 5); mild OSA (AHI
5 to 19); moderate OSA (AHI 20 to 39); and severe OSA (AHI 40). In
the group of subjects with AHIs of < 5 (ie, the no-OSA
group), 37% had PSG evidence of periodic leg movements (defined as a
periodic leg movement index of 5 per hour of sleep). Another 31.5%
of subjects had PSG findings that were consistent with a disorder of
initiation and maintenance of sleep (defined as sleep latency of 20
min or sleep efficiency of 
80%). The rest of the subjects (31.5%)
did not have a significant abnormality revealed on PSG.
Baseline PSG
All patients received a baseline diagnostic PSG at the UAH Sleep
Disorders Laboratory. Recordings were performed overnight with
continuous monitoring of EEG, electro-oculogram, chin and intercostal
electromyograms, oronasal airflow (by thermistor), chest and abdominal
respiratory movements, oximetry, anterior tibialis electromyogram, body
position sensor, and snoring noise sensor. Digitized signals were
stored on optical disks and were analyzed using a computer program
(Discovery Outcomes; Livingston, TN). Manual scoring was
performed by a trained, certified technician to verify the
results of the automated scoring system in every case. The sleep
recordings were reviewed by an American Board of Sleep
Medicine-certified sleep specialists who provided a descriptive
diagnostic interpretation of the PSGs.
The scoring of sleep staging was done using published criteria.19 An apnea episode was defined as a cessation of oronasal airflow for > 10 s. A hypopnea episode was defined as a diminution of the amplitude of respiratory signals by > 50% for > 10 s with or without desaturation. An obstructive respiratory event was scored when there was evidence of paradoxical chest and abdominal movements. A central respiratory event was scored when both the chest and abdominal respiratory movements were diminished or absent.
Follow-up Protocol
All patients were assessed at baseline (after undergoing the PSG
and before receiving CPAP therapy), and at 3 and 12 months of
follow-up. During each visit, the patients’ health status was
determined using the 36-item medical outcomes study short form (SF-36)
questionnaire.20
We chose this survey instrument for
several reasons. It has been used extensively in other similar studies,
which facilitates cross-comparisons of our findings with those of
previous studies.8
9
Second, the SF-36 has been shown to
have excellent reliability, validity, and responsiveness for patients
with OSA.21
Third, the SF-36 has established normative
scores for comparisons, making the scores easily understood by health
services researchers and policy makers.22
Fourth, compared
to other generic health status measurements, the SF-36 has been shown
to be more responsive to clinically relevant changes.23
The SF-36 is a 36-item survey instrument that quantitatively measures physical functioning and emotional health.20 Each variable has a potential score range of 0 (worst possible health) to 100 (best possible health). There are eight domains in the SF-36, as follows: physical functioning; role-physical; bodily pain; general health perception; vitality; social functioning; role-emotional; and emotional health. These domains can be grouped into two categories, producing physical and emotional (component) summary scores.24
A study team member, who was not aware of a patient’s AHI status and did not participate in any other aspects of clinical management, conducted all interviews of the patients to determine their health status at baseline, at 3 months of follow-up, and at 12 months of follow-up. To minimize possible biases during the interview process, we employed one person to conduct all the interviews using standardized survey techniques.25 A different individual then collated all the SF-36 data and merged it with the baseline PSG data (contained in a different database). During the interview, only the SF-36 data were ascertained; no other discussions occurred. This was done to minimize the risk for differential follow-up bias. We followed the study patients for 12 months. Aside from CPAP therapy, we did not introduce any other interventions to these groups. Referring physicians were permitted to modify general medical therapy as required.
Statistical Analysis
The means and SDs of continuous variables were compared using
the Student two-tailed t test. Nonnormally distributed
variables were compared using the Wilcoxon rank sum test. Ordinal and
binary variables were compared using a 
2 test.
The primary outcome was the emotional summary component of the SF-36
questionnaire. We compared the change in this measure between those
patients with AHIs 20 (and treated with CPAP) and those with AHIs
< 20 using the Wilcoxon rank sum test. Since daytime sleepiness is
the cardinal symptom of OSA,2
we anticipated that CPAP
therapy would produce the largest benefits in the vitality domain of
the HRQL spectrum in patients with OSA. Accordingly, the secondary end
point was to compare changes in the vitality domain scores between
these two groups over a 12-month period using the Wilcoxon rank sum
test.
As there were some baseline demographic differences between the two
groups (Table 1
), we used a multiple regression model to determine the
independent effects of CPAP therapy on the SF-36 scores. The model
included the three most important potential confounders, age, gender,
and body mass index (BMI), as covariates. The CPAP/no-CPAP group
variable was the explanatory variable, and the SF-36 scores were the
response variables. Age was divided into the following three mutually
exclusive categories: 18 to 39 years; 40 to 59 years; and 60 years.
The BMI was divided into the following quartiles: quartile 1 (BMI,
< 26.2 kg/m2); quartile 2 (BMI, 26.3 to 30.8
kg/m2); quartile 3 (BMI, 30.9 to 37.4
kg/m2); and quartile 4 (BMI, > 37.4
kg/m2). To increase the efficiency of this
multiple regression model, we employed a stepwise selection process in
which covariates with p values of 0.30 were selected and those
with p values of 0.20 were retained in the final model. Continuous
variables were expressed as the mean ± SD, unless otherwise
indicated. All analyses were performed with appropriate software (SAS,
version 8.1; SAS Institute; Cary, NC).
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The baseline characteristics of those with AHIs of < 20 and 20
are shown in Table 1
. Those with AHIs of 20 were slightly older and
more obese than those with AHIs of < 20. Moreover, the former group
contained more men than the latter group. The baseline physical and
emotional summary scores were, however, similar between the two groups.
Table 2
shows the SF-36 scores for the groups of patients with AHIs of 20
and < 20. The baseline emotional and physical component summary
scores were similar between the two groups (Fig 1
). However, by the third month of follow-up, patients with AHIs of
20 (and who had been treated with CPAP) had a higher emotional
summary score than those with AHIs of < 20 (and who had not been
treated with CPAP). The largest differences were observed in the
vitality domain, a finding that is consistent with the known effects of
CPAP in abolishing daytime sleepiness and lethargy that are associated
with OSA.8
9
Most importantly, the early benefits of CPAP
therapy observed at 3 months of follow-up were maintained to 12 months
of follow-up. The emotional summary scores and, in particular, the
vitality scores remained higher than at baseline and were higher than
those observed for patients who had not been treated with CPAP,
suggesting that the beneficial short-term effects of CPAP on emotional
HRQL are sustainable over a much longer period of time if therapy is
continued (Table 2) . We did not observe any significant improvements in
the physical summary scores or in any individual physical domain with
CPAP therapy.
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Patients with the lowest baseline emotional summary scores experienced the largest gains in their HRQL over a 12-month period. Those with the highest baseline scores experienced the smallest gains (Fig 2 ; p = 0.001). These findings are consistent with those of prior reports8 9 and suggest that OSA patients with a poor (self-perceived) HRQL are more likely to receive benefits from CPAP therapy than those with a good or excellent baseline HRQL status, irrespective of their baseline AHIs. We analyzed the data for compliance at 3 months of follow-up and at 12 months of follow-up. After adjustments for age, sex, and baseline AHI, patients with poorer HRQL (emotional summary score) at baseline were also more likely to be compliant with CPAP therapy than were those with higher HRQL baseline scores (p = 0.042) at 3 months of follow-up, but not at 12 months of follow-up (p = 0.116).
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40) OSA. Compared to those persons without OSA, vitality
scores at 3 months of follow-up were 5.7 U higher (95% CI, 0.4 to
11.0) and 12.3 U higher (95% CI, 8.0 to 16.6) in those with moderate
and severe OSA, respectively. Similarly, at 12 months of follow-up, the
vitality scores were 12.4 U higher (95% CI, 7.5 to 17.3) in the severe
OSA group compared to the no-OSA group (Fig 3
).
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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40. Most importantly, these improvements were
maintained over a 12-month period, suggesting that CPAP therapy is
effective in improving the long-term HRQL of patients with OSA. Second,
our study findings suggest that most OSA patients referred for PSG have
poor HRQL. Whereas the mean emotional and physical summary scores
reported22
for the Canadian men and women were 51.4 (95%
CI, 51.0 to 51.8) and 51.3 (95% CI, 50.9 to 51.7), respectively, the
mean emotional and physical summary scores for our group of OSA
patients were only 44.4 and 40.5, respectively. However, 3 months of
CPAP therapy was associated with a normalization of emotional summary
scores, but not of physical summary scores. Third, the baseline
emotional summary scores were excellent predictors of long-term
improvements in the HRQL of OSA patients, independent of the baseline
AHI. These data suggest that OSA patients with good subjective HRQL
scores at baseline are less likely to derive benefits from CPAP therapy
than those with poor baseline HRQL scores. Taken together, our data
suggest that baseline SF-36 scores, along with other clinical and PSG
information, should be considered in management decisions regarding
CPAP therapy for OSA patients.
The improvements observed in the SF-36 scores with CPAP therapy are not
only statistically significant but also clinically meaningful. An
effect size of 0.8 between the component summary scores of those
patients with AHIs of 20 (and who had been treated with CPAP) and
those patients with AHIs of < 20 (and who had not been treated with
CPAP) is considered to be a large change.9
In our study,
the changes in the adjusted emotional summary scores were 3.15 U higher
in the CPAP group than in the no-CPAP group after 12 months of
follow-up (Table
3), suggesting that
CPAP therapy produces clinically relevant improvements in the overall
emotional well-being of OSA patients.
Several limitations of our study should be addressed. First, our study did not have a control group that was selected on the basis of random allocation or a group that was treated with a placebo. This may have introduced a placebo effect into our findings, leading to an overestimation of the benefits of CPAP therapy. However, a recent meta-analysis26 has suggested that, while some placebo effect is likely to be present when using a subjective end point such as HRQL, these effects are generally small and unlikely to explain away the large differences in the HRQL scores (in the vitality domain) that were found in the present study. Second, as with most observational studies, there is also the concern for confounding. In order to make the AHI groups as comparable as possible, we used patients from the same referral center and controlled for the differences in baseline demographic factors through well-accepted statistical methods.27 While there were some baseline differences between the two AHI groups, the use of modeling techniques did not appreciably change the unadjusted results, providing some evidence that our findings were consistent, robust, and unlikely to have been confounded by external factors. Third, we did not use a disease-specific instrument to measure the HRQL gains with CPAP therapy. Although disease-specific instruments are more sensitive and responsive to small changes in HRQL, they may miss potential (adverse) effects of CPAP therapy on health domains not related to daytime sleepiness, which generic instruments are more likely to capture.28 Furthermore, generic instruments, unlike specific ones, allow broader comparisons with other interventions and other disease processes, which are important for health policy formulation and health services research.28 Finally, our data should not be extended to patients with symptoms that are consistent with OSA whose baseline AHIs are < 20 because in the present study we excluded patients with AHIs of < 20 who received CPAP therapy.
In summary, our study findings show that CPAP is an effective long-term therapy for improving the emotional health status of patients with OSA in the community, which is consistent with findings from previous long-term studies.17 29 30 31 It is clear that many untreated OSA patients experience poor HRQL. Rapid and sustained improvements in their health status can be achieved through CPAP therapy. Future studies are, however, needed to determine whether these subjective improvements translate into lower OSA-related morbidity, mortality, and health-care costs for patients and society.
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Acknowledgements |
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Footnotes |
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Dr. Sin was supported by a New Investigator Award from the Canadian Institutes of Health Research and a Population Health Investigator Award from the Alberta Heritage Foundation for Medical Research. This project was sponsored in part through an unrestricted research grant from the Alberta Lung Association.
Received for publication November 2, 2001. Accepted for publication May 23, 2002.
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References |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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This article has been cited by other articles:
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  R. K. Kakkar and R. B. Berry Positive Airway Pressure Treatment for Obstructive Sleep Apnea Chest, September 1, 2007; 132(3): 1057 - 1072. [Abstract] [Full Text] [PDF]
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D. J. Schwartz, W. C. Kohler, and G. Karatinos Symptoms of Depression in Individuals With Obstructive Sleep Apnea May Be Amenable to Treatment With Continuous Positive Airway Pressure Chest, September 1, 2005; 128(3): 1304 - 1309. [Abstract] [Full Text] [PDF]
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