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(Chest. 2004;126:1241-1247.)
© 2004 American College of Chest Physicians

Predictive Factors of Quality-of-Life Improvement and Continuous Positive Airway Pressure Use in Patients With Sleep Apnea-Hypopnea Syndrome*

Study at 1 Year

Patricia Lloberes, MD; Sergi Martí, MD; Gabriel Sampol, MD; Antoni Roca, MD; Teresa Sagales, MD; Xavier Muñoz, MD and Montserrat Ferrer, MD

* From the Servei de Pneumologia and Servei de Neurofisiologia Clínica, Hospital Vall d’Hebron, Barcelona; and Institut Municipal d’Investigació Mèdica, Hospital del Mar, Barcelona, Spain.

Correspondence to: Patricia Lloberes, MD, Servei de Pneumologia, Hospital General Vall d’Hebron, Passeig Vall d’Hebron 119-129, 08035 Barcelona, Spain; e-mail: plloberes{at}vhebron.net


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objectives: To assess predictive factors of quality-of-life (QoL) improvement and continuous positive airway pressure (CPAP) use in patients with sleep apnea-hypopnea syndrome (SAHS) after 1 year of treatment with CPAP.

Design: Observational, prospective cohort study.

Setting: Sleep unit in a university hospital.

Patients: One hundred thirty-three consecutive patients with an indication for CPAP treatment.

Measurements and results: Nottingham health profile (NHP) questionnaire, Epworth sleepiness scale score, and objective CPAP use (time counter in the CPAP device) were assessed at baseline and after 3 months and 12 months of CPAP use. Multivariate logistic regression was used to identify predictive factors of CPAP use and improved QoL. At 1 year, 101 patients (76%) were still using CPAP; of these, 88 patients (66%) completed all the follow-up questionnaires. QoL was lower before treatment, compared with the general population, and all dimensions of the NHP, except social isolation, improved significantly from baseline in patients regularly using CPAP, reaching levels comparable to those of the general population at 1 year. Only minimum oxyhemoglobin saturation at diagnostic polysomnography was associated with the degree of QoL improvement at 1 year. Only the NHP and the apnea-hypopnea index (AHI) at baseline were significantly associated with hours of CPAP use at 1 year.

Conclusions: Compared to the general population, patients with untreated SAHS had a lower QoL, which improved to the level of the general population after 3 months of CPAP therapy and persisted at 1 year of treatment with CPAP. The only predictor of QoL improvement was minimum nocturnal oxygen saturation at baseline. Higher AHI and worse QoL at baseline were predictors of hours of CPAP use.

Key Words: CPAP compliance • quality of life • sleep apnea


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Several studies have shown that general health status in patients with sleep apnea-hypopnea syndrome (SAHS) is impaired,12 and that even modest sleep-disordered breathing is associated with lower health status comparable to that observed in other chronic conditions such as diabetes, arthritis, angina, back problems, or hypertension.34 Continuous positive airway pressure (CPAP) therapy can improve health status, quality of life (QoL), and neuropsychological deficits in these patients.5678 However, although the short-term clinical effects of CPAP have been well documented,91011 long-term clinical effects of CPAP have not been well reported. Furthermore, factors that are predictive of improved compliance with CPAP have not been clearly established. This can be explained, in part, by the lack of a consistent relationship between SAHS severity, as evaluated by conventional nocturnal measures, and the extent of daytime impairment. Therefore, it is important to assess the impact of SAHS on QoL and its relationship with CPAP compliance. Although generic QoL questionnaires in SAHS have shown substantial responses to CPAP treatment, their value as a predictor of CPAP response is unknown. The present study was designed to assess predictive factors of QoL improvement and hours of use of CPAP among patients using CPAP after 1 year of treatment.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
The population studied consisted of 133 consecutive patients with SAHS recruited from our sleep unit, in whom CPAP treatment was indicated. All patients underwent diagnostic polysomnography, and the CPAP pressure was selected after a titration study. CPAP treatment criteria were as follows: severe clinical symptoms (active somnolence not attributable to other causes) along with an apnea-hypopnea index (AHI) > 15 or an AHI > 30 with mild-to-moderate clinical symptoms, systemic hypertension, or cardiac disease.12

Anthropometric data, oxyhemoglobin saturation (SaO2) while awake, and daytime sleepiness, assessed by the Epworth sleepiness scale (ESS),13 were recorded at baseline. From all the polysomnography parameters, only mean and minimum SaO2, and AHI were introduced into our database and used for the analysis. From the CPAP titration study, the only parameter recorded was optimal CPAP, selected as the minimal pressure that abolished snoring, apnea, and hypopneas, making sure that patients achieved the supine position and one rapid eye movement sleep stage. Patients were supplied with CPAP devices that were financed by the National Health Service of our country. Patients were followed up at 3 months and 12 months of CPAP therapy. At each visit, the importance of CPAP use was reinforced, and data on weight and ESS score were recorded. To assess compliance, the objective use of CPAP was recorded by reading the built-in clock counter of the CPAP device, and dividing the difference of hours of use from the last visit by the number of days elapsed. The study was approved by the ethics committee of the hospital, and patients gave their informed consent to participate in the 1-year follow-up.

QoL Measurements
QoL was assessed by the Nottingham health profile (NHP), a multidimensional generic instrument that has been found to be appropriate for Spanish patients with SAHS.14 It contains 38 items classified into six dimensions: pain, sleep, emotional reactions, physical mobility, social isolation, and energy. The NHP questionnaire was self-administered by patients before treatment and after 3 months and 12 months. Scores were calculated as a count of the number of items endorsed, and ranged from 0 (no perceived distress) to 100 (maximum perceived distress).15 For patients with missing data, scores were calculated only for dimensions with a maximum of one item missing out of three. The imputation method consisted of assigning the mean value of the other items belonging to the dimension.

Analysis
Data are expressed as mean (SD). Differences in baseline characteristics according to follow-up outcome were tested using the {chi}2 or t test, as appropriate. QoL was compared with that of the 50- to 59-year-old range group of the general population of Barcelona, which served as a reference value.15 To assess the association of basal characteristics with the change in total NHP score, a generalized estimating equation for repeated measures was constructed including the three measurements of the NHP (baseline, 3 months, and 1 year); this method takes into account the correlation between subjects. Patients were classified as having "good use" if their mean daily CPAP use was ≥ 4 h; otherwise, they were classified as having "poor use."10 Multivariate logistic regression was used to identify factors that were predictive of good CPAP compliance (use of ≥ 4 h) at 3 months and 1 year of treatment.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Characteristics of the patients studied and follow-up results at 1 year of the 133 patients recruited are shown in Table 1 and Figure 1 , respectively. Eleven patients were unavailable for follow-up, 17 patients abandoned CPAP (12.8%), and 4 patients died (3%). At 1 year, 101 patients were still using CPAP (76%), but 13 of these patients did not complete all questionnaires and were considered unavailable for analysis purposes. Thus, 88 patients who were still using CPAP and had complete follow-up were used for analysis (66% of the initial population). Characteristics of patients in the different groups were similar except for a significantly lower AHI and ESS scores in patients who abandoned CPAP and in those who died, respectively, compared with the group studied. The mean hours of CPAP use and ESS score did not differ among patients who completed follow-up and those who were still using CPAP at 1 year, but did not complete all NHP questionnaires: 5.8 (2.2) vs 5.7 (2.5) and 5.2 (3.3) vs 6.5 (4.2), respectively.


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  		Table 1.. Characteristics of Patients*

 


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  		Figure 1.. Follow-up data of patients included in the study.

 
Outcome measures at 1 year of treatment are shown in Table 2 . Most patients (77.3%) used CPAP for ≥ 4 h. No significant differences were observed in baseline characteristics, including baseline body mass index, AHI, CPAP, ESS, and baseline NHP among patients using CPAP > 4 h or < 4 h: mean, 6.6 h (1.5) and 2.5 h (1.4), respectively. Body mass index was similar in the two groups both at baseline (mean, 33.6 [6] vs 33 [7]) and at 1 year of treatment (mean, 32.8 [6.3] vs 32.5 [6.6]). However, patients using CPAP < 4 h showed a significantly higher mean baseline SaO2 while awake compared with those using CPAP > 4 h: 95.5% (1.78) and 93.9% (3.6), respectively; p < 0.02.


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  		Table 2.. Outcome Measures at 1 Year According to Compliance With CPAP*

 
NHP dimensions of energy, emotional reactions, and sleep were the most impaired. Considering all patients, NHP results had improved in 67 patients (76.1%) at 1 year, showed no change in 7 patients (8%), and worsened in 14 patients (15.9%). All NHP dimensions, except social isolation, had improved significantly after 1 year of CPAP treatment. The evolution of each NHP dimension from baseline to 3 months and 12 months of CPAP use, compared with the general population, is depicted in Figure 2 . Notice the positive change in all NHP dimensions, which approached the levels of the general population. The positive change was most evident for the dimensions of energy, emotional reactions, and sleep.



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  		Figure 2.. NHP scores of patients with SAHS at baseline, after 3 months and 12 months of CPAP treatment, and of the general population.

 
Results of the generalized estimating equation model obtained to examine the association of basal characteristics with repeated measures of NHP total scores (3 months and 1 year) are shown in Table 3 . The NHP total score differences between groups of patients are shown in the left part of Table 3. From baseline clinical characteristics, only the age explained statistically significant differences between patients in total NHP scores. Patients > 64 years old presented worse QoL than the reference group, which includes patients < 50 years old (NHP total score 17.5 points higher, p = 0.007). The differences within patients according to factors evaluated are shown in the right part of Table 3, and coefficients should be interpreted as the difference in change by year of the NHP total score experienced by any given typical patient who exhibits the characteristic compared with the reference category. The NHP change after 1 year of treatment experienced by patients with characteristics equal to the reference category of all the factors introduced into the model was - 19.6 (95% confidence interval [CI], - 33.7 to – 5.47). From the polysomnography parameters recorded (AHI, mean and minimum SaO2), the minimum SaO2 presented a higher correlation with NHP and was introduced into the model. Minimum SaO2 was the only factor significantly associated with change in NHP total score. Patients with minimum SaO2 > 60% experienced lower improvement in QoL. For example, applying coefficients of the model, patients with minimum SaO2 between 60% and 79% experienced a change of - 11.4 (– 19.6 + 8.2) points compared to the – 19.6 points of improvement of the reference group (minimum SaO2 < 60%). Hours of CPAP use > 4 h or < 4 h were not associated with NHP improvement.


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  		Table 3.. Association of Basal Patient Characteristics With Repeated Measures of NHP Total Score at 3 Months and 1 Year of Treatment

 
The association between baseline characteristics of patients and hours of CPAP use at 3 months and at 1 year of treatment is shown in Table 4 . At 3 months, no factors predictive of good CPAP compliance were identified, except male gender, with respect to women. After 1 year of treatment, NHP and AHI at baseline were significantly associated with hours of CPAP use. Patients with AHI values between 50 and 78 and/or NHP total scores ≥ 9.95 at baseline were more likely to be good users of CPAP.


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  		Table 4.. Association of Basal Characteristics With Good Compliance (≥ 4 h) at 3 Months and at 1 Year of Treatment

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
This study showed that patients with SAHS have QoL impairment that can be improved to general population levels when treated with CPAP. This improvement was observed at 3 months and persisted at 1 year of treatment, and was evident for all NHP dimensions, especially emotional reactions, sleep, and energy (the most impaired dimensions before treatment). Minimum SaO2 at diagnostic polysomnography was a significant predictor of improved QoL. Severe SAHS (AHI > 50) and an impaired NHP score were predictive factors of > 4 h of CPAP use. Interestingly, daytime sleepiness assessed by the ESS score was not associated with NHP improvement or longer CPAP use, and patients using CPAP for > 4 h or < 4 h showed no differences in the magnitude of QoL and somnolence improvement.

The use of CPAP over long follow-up periods has mainly been assessed in retrospective studies.616 Several prospective series1718192021 show long-term use of CPAP in approximately 60% of patients. In our study, 76% of the patients recruited were still using CPAP at 1 year, and most used the device for > 4 h. Many authors have found CPAP compliance to be related to SAHS severity, as evaluated by AHI, hypoxemia, or baseline hypersomnolence,22 or to the difference in mean SaO2 during sleep and in hypersomnia scores before and after treatment by nasal CPAP.161718 Others have shown CPAP use to be linked to prior sleepiness rather than to illness severity,6 improvement in subjective sleepiness, SAHS symptoms, vitality, and general well-being,519 or failed to show predictors of compliance.21 Our results suggest that there are no predictive factors of CPAP use at 3 months, but that both disease severity, assessed by AHI, and impaired QoL before treatment predict the use of CPAP at 1 year.

Although increased use of CPAP could be presumed to produce greater improvement, our results suggest that regular users of CPAP achieve benefits despite the number of hours of CPAP use, since patients using CPAP for > 4 h or < 4 h showed a similar QoL and somnolence improvement. The minimum therapeutic usage of CPAP remains unknown. Hers et al23 demonstrated a clinically important residual benefit that persists in the latter part of the night after CPAP withdrawal. Therefore, patients might adjust their CPAP use to a level that produces subjective benefits in daytime function.

As for CPAP use, a consistent correlation between SAHS severity, as defined by the AHI, and health profile indexes has not been found.152425 D’Ambrosio et al5 showed the magnitude of improvement in QoL to be related to the degree of QoL impairment before treatment, rather than to severity of the disease as measured by respiratory disturbance and arousal indexes. In our study, the worse the degree of hypoxemia at diagnostic polysomnography, the more the patients improved their QoL. Other studies2627 have found an association between hypoxemia and impaired neuropsychological and cognitive function.

Generic QoL questionnaires have proved useful for assessing the wide-ranging impact of SAHS on perceived health. Jenkinson et al2728 compared different approaches to measuring health in patients with SAHS: the patient-generated index (PGI), the EuroQoL, and the Short-Form-36 (SF-36). The PGI resulted in the highest level of change of all the measures. The EuroQoL yielded contrary results to the findings of both the PGI and the SF-36. In SAHS patients, SF-36 scores were lower than those of the general population at baseline, but improved to normative levels after treatment.330 The NHP has been used in several studies in patients with SAHS to assess QoL before and after treatment. In one study,24 NHP was more impaired in patients with SAHS than in nonsnoring healthy subjects, but neither general health status nor somnolence were related to SAHS severity expressed as AHI. Greater improvement in NHP was found with CPAP than conservative measures alone, at 3 months, in the domains of energy and social isolation, with a marginal trend in the dimensions of physical mobility and emotional reactions, and no differences in pain and sleep,11 which is in agreement with our study, in which improvements were observed in all NHP domains except social isolation. This improvement was evident at 3 months and persisted at 1 year. Two studies3132 demonstrated a good mean score in each dimension of the NHP in 75% of patients who continued CPAP treatment for > 6 months. Perceived health was significantly related to improvement in symptoms, overall satisfaction, and objective compliance.3132 Another study5 found that the magnitude of improvement was related to the degree of QoL impairment prior to treatment rather than to disease severity. We found that the only predictor of QoL improvement was minimum SaO2 < 60%, regardless of AHI, ESS score, or age at baseline. This could suggest that minimal SaO2 during the night has an effect on QoL perception that is not mediated by daytime somnolence, at least as measured by the ESS. One limitation of this study is that the magnitude of change in AHI and SaO2 during the CPAP titration night was not evaluated as a possible predictor of QoL and CPAP compliance. During CPAP titration studies, CPAP pressure was increased manually until snoring, apneas, and hypopneas were abolished, making sure that patients achieved the supine position and at least one rapid eye movement sleep stage. Taking into account that the majority of patients achieved a normal AHI during the titration night, the magnitude of change in AHI is highly correlated with the AHI impairment at baseline.

Reference values in the NHP were obtained from a study of 1,220 persons from our general population15; thus, persons with chronic conditions were included. Although disease-specific questionnaires are usually more sensitive to small changes in health, one advantage of generic QoL questionnaires is that they ask general questions that could apply to any disease or health state and permit a comparison across diseases. Our patients with SAHS showed NHP scores similar to those described in patients with chronic obstructive lung disease and angina pectoris,33 lower than people with rheumatoid arthritis, and higher than those with migraine or the healthy population.33

In conclusion, this study shows that patients with SAHS in whom CPAP is indicated have a lower QoL when compared to the general population. In patients using CPAP, QoL improved at 3 months to the level of the general population, and this improvement persisted at 1 year of treatment, independently of the hours of CPAP use. SAHS severity assessed by AHI and QoL impairment were predictive factors of hours of CPAP use, while the degree of baseline nocturnal hypoxemia was the only predictive factor of QoL improvement.


   Acknowledgements
 
The authors thank Christine O’Hara for manuscript correction, and Maite Valdeolivas and Rosa Llòria for secretarial support.


   Footnotes
 
Abbreviations: AHI = apnea-hypopnea index; CI = confidence interval; CPAP = continuous positive airway pressure; ESS = Epworth sleepiness scale; NHP = Nottingham health profile; PGI = patient-generated index; QoL = quality of life; SAHS = sleep apnea-hypopnea syndrome; SaO2 = oxyhemoglobin saturation; SF-36 = Short-Form-36

This study was supported, in part, by Red Respira (Instituto Carlos III. FIS RTYC-CO3/11)-SEPAR.

Received for publication September 5, 2003. Accepted for publication May 18, 2004.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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