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(Chest. 2006;129:638-643.)
© 2006 American College of Chest Physicians

Equivalence of Autoadjusted and Constant Continuous Positive Airway Pressure in Home Treatment of Sleep Apnea*

Yvonne Nussbaumer, MD; Konrad E. Bloch, MD, FCCP; Therese Genser and Robert Thurnheer, MD, FCCP

* From the Pulmonary Division (Drs. Nussbaumer and Thurnheer and Ms. Genser), Department of Internal Medicine, Kantonsspital Münsterlingen, Münsterlingen; and Pulmonary Division (Dr. Bloch), Department of Internal Medicine, University Hospital of Zurich, Zurich, Switzerland.

Correspondence to: Robert Thurnheer, MD, FCCP, Pulmonary Division, Department of Internal Medicine, Kantonsspital Münsterlingen, 8596 Münsterlingen, Switzerland; e-mail: robert.thurnheer{at}stgag.ch

Abstract

Whether computerized autoadjusted continuous positive airway pressure (aCPAP) is effective or even superior to constant continuous positive airway pressure (cCPAP) in the treatment of obstructive sleep apnea syndrome (OSAS) is still controversial. We performed a randomized, double-blind, controlled, cross-over trial comparing efficacy of sleep apnea home therapy by a novel aCPAP machine (REMStarAuto; Respironics; Murrysville, PA) operated in autoadjusted or constant mode. Thirty sleep apnea patients were recruited consecutively. Mean baseline Epworth sleepiness scale (ESS) score was 12.7 ± 0.6 (± SD), mean sleep resistance time was 26 ± 2 min (Osler test; Stowood Scientific Systems; Oxford, UK), and mean apnea-hypopnea index (AHI) was 41.1 ± 3.6 h. Patients were randomly assigned to 1 month of home therapy with aCPAP followed by 1 month with cCPAP, or vice versa. After 1 month with treatment, the mean ESS score, sleep resistance time, and AHI were significantly improved (6.6 ± 0.6, 37 ± 1 min, and 4.6 ± 0.7 h, respectively; all p < 0.05 vs baseline). Similar effects were achieved with cCPAP (p = not significant vs aCPAP). Twenty-six patients preferred aCPAP, and 4 patients preferred cCPAP (p < 0.001). We conclude that patients with OSAS preferred aCPAP over cCPAP in the initial phase of therapy. The effectiveness aCPAP in improving major outcomes was equivalent to cCPAP. Since aCPAP does not require initial titration, it is a simple and promising modality for sleep apnea home therapy.

Key Words: auto-continuous positive airway pressure • continuous positive airway pressure • randomized trial • sleep apnea • treatment • vigilance

The obstructive sleep apnea syndrome (OSAS) is an important disorder affecting between 2% and 4% of adults.1 OSAS is associated with excessive daytime sleepiness, impaired quality of life, and risk of traffic accidents.23 Continuous positive airway pressure (CPAP) applied to the nose, the standard treatment for OSAS, improves vigilance, quality of life, and traffic safety.456 The therapeutic mask pressure that abolishes apnea, hypopnea, and snoring in all sleep stages and body positions has conventionally been determined by "manual" in-laboratory titration.7 This is expensive and responsible for long waiting lists. In addition, the therapeutic CPAP determined in a single titration night is a tradeoff between pressure-related side effects and efficacy in preventing upper-airway obstruction. This is because the pressure required to maintain upper-airway patency changes during a night depending on body position, sleep stage, nasal obstruction, ingestion of alcohol or hypnotic agents,8 and over time based on changes in body weight and upper-airway properties. This variability of CPAP requirement has generated considerable interest in devices adjusting mask pressure by feedback control according to patterns of pressure, flow, or other signals during treatment (autoadjusted CPAP [aCPAP] devices). Autoadjustment of treatment pressure allows for a decrease in CPAP when apneas and hypopneas disappear, and an increase when respiratory disorders reappear. This has led to the assumption that continuous adaptation of mask pressure to the actual needs of the patient might improve effectiveness of therapy by preventing sleep disturbances from unnecessarily high mask pressures, by enhancing comfort and treatment adherence.9 Mean mask pressure applied during aCPAP home therapy is generally lower than the manually titrated pressure.1011 Compliance with aCPAP was higher than with constant CPAP (cCPAP) in some studies912 but not all studies.1011 Whether aCPAP home therapy results in similar or even greater improvement of subjective and objective sleepiness and respiratory disturbances as cCPAP is still a matter of debate.101314

Since aCPAP has the potential to enhance comfort and simplify sleep apnea therapy, we tested the hypothesis that treatment effects are equivalent when the same machine (REM-Star Auto; Respironics; Murrysville, PA) is operated in the aCPAP vs cCPAP mode during the initial phase of home therapy. A prospective, double-blind randomized, cross-over protocol was employed. Main outcomes were the differences between the treatment modes in subjective and objective sleepiness, quality of life, nocturnal breathing disturbances, and compliance, as well as preference for one or the other mode. Some of these results have been reported in the form of an abstract.15

Materials and Methods

Patients
Consecutive patients with excessive sleepiness and apnea-hypopnea index (AHI) >10 obstructive events per hour were included. Patients with congestive heart failure, chronic rhinitis, and other sleep disorders were excluded. The protocol was approved by the local ethics committee. For the diagnosis of sleep apnea, unattended home sleep studies were performed with a 7-channel respiratory polygraph (PolyMESAM; MAP; Martinsried, Germany),16 recording nasal airflow,17 thoracoabdominal movement, ECG, oxygen saturation, body position, and leg movement. The polygraph was mounted by the study nurse in the outpatient clinic. Time periods from 11 PM to 5:30 AM were taken for automated analysis. All sleep studies were manually controlled scoring 1-min epochs. Apnea was defined as a cessation of airflow at the nose for at least 10s, and hypopneas were scored when a decrease in the amplitude of airflow signal to < 50% of the level prevailing before the event accompanied by a fall in oxyhemoglobin saturation of at least 3% was identified. Home monitoring has been shown to be as reliable as laboratory polysomnography in the prediction of success of nasal CPAP treatment, at least in patients without significant comorbidity.18

Blower Machine
The REMStar Auto device, an aCPAP machine programmable by an insertable computer chip card, was employed. In six patients, the 90th pressure percentile applied by the REM-Star Auto device was not statistically different from the ninetieth percentile applied by a previously validated device (Res Med AutoSet; Respironics)11 during 2 titration nights, one with each device. Mean 90th pressures percentiles were 7.0 (SE, 0.37) and 7.9 (SE, 0.54) cm H2O, respectively (p = not significant [NS]).

Protocol
Patients were instructed that they would sleep with a blower device working in different modes without giving further information about the modes. The patients were treated over two periods of 1 month with aCPAP and cCPAP modes, respectively, applied by the same device in random order. At the time of randomization, a pair of two identically looking chip cards was assigned to each patient. One card contained the code to operate the CPAP device in constant mode at the 90th pressure percentile applied during 1-night aCPAP titration. The other card contained the code to operate the CPAP device in aCPAP mode with a pressure range from 5 to 15 cm H2O. Patients were instructed to use the CPAP device for 1 month with one of the two cards, and for another month with the other card. Patients and attending physicians were blinded to treatment modes and order of application.

Measurement and Outcomes
Subjective sleepiness was assessed by the Epworth sleepiness scale (ESS).19 Health-related quality of life was assessed by the Short Form-36 (SF-36) questionnaire.20 Symptoms, treatment benefits, and side effects were rated by patients on visual analog scales ranging from 0 to 100 mm. Daytime vigilance was evaluated by the Osler test2122 (Stowood Scientific Systems; Oxford, UK). The mean time until seven successive responses to a light signal were missed, and the mean number of missed stimuli per minute23 were recorded during two test sessions on the same day at 9 AM and 11 AM.

Statistical Analysis
Data are summarized as mean ± SE. Repeated evaluations were performed with paired t tests or analysis of variance. Preference of CPAP mode was calculated with the Fisher exact p test. The agreement between applied mask pressure during cCPAP and aCPAP treatment was assessed by the method of Bland and Altman.24 The effect size was calculated as ratio of the mean difference to baseline to the SD of the mean at baseline.25 An effect size of 0.2 is considered small, 0.5 is considered intermediate, and 0.8 is considered high.

According to Jones and coworkers,26 equivalence between treatment modes was assumed if the 95% confidence interval (CI) of an observed difference fell entirely within a specified equivalence range. Differences in the ESS score of < 2 points,5 in the SF-36 vitality score of < 10 points,4 in AHI of < 5/h, and in sleep resistance time < 4 min were considered to reflect equivalence.5 With a sample size of 30 patients, the study was powered with > 80% to detect the following significant differences in major outcomes ({alpha} < 0.05): ESS score, 1; SF-36 vitality score, 11; AHI, 5/min; sleep resistance time, 3 min.

Results

Patients
Thirty-four patients were included; 4 of these patients did not complete the protocol. Two patients were given humidifiers, one stopped treatment because of claustrophobia, and another subject was unavailable for follow-up. Results from 27 men and 3 women were available for analysis. The mean age was 49 years (SE, 2 years; range, 29 to 65 years), mean body mass index was 31.1 kg/m2 (SE, 0.6 kg/m2), and mean neck circumference was 42.7 cm (SE, 2.2 cm).

Outcomes
The effect of treatment with aCPAP was compared to that with cCPAP and to baseline. Main results are given in Table 1 . Individual results for subjective vigilance as well as for AHI are shown in Figures 1, 2 .


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  		Table 1.. Effects of aCPAP and cCPAP Therapy*

 

Figure 1
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  		Figure 1.. Individual results of ESS scores at baseline and with the two different treatment modes.

 

Figure 2
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  		Figure 2.. Individual results of AHI at baseline and with the two different treatment modes.

 
Subjective Assessment
There was a significant and clinically relevant improvement in symptoms by both treatment modalities to a similar degree. Mean decrease in the ESS score was > 6 points for cCPAP and aCPAP. The effect size was 1.99 for cCPAP and 2.07 for aCPAP. The 95% CI of the mean difference between the treatment modalities was – 1.6 to + 1.1, suggesting equivalence (Fig 3 ). The SF-36 vitality score was significantly improved with either treatment, whereas in the other domains of the SF-36 no significant differences to baseline were found (Table 1).


Figure 3
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  		Figure 3.. To evaluate whether the effects of aCPAP and cCPAP were equivalent, the 95% CIs of the differences in major outcomes are displayed as solid horizontal lines. Differences are computed as values during autoadjusted minus corresponding values during cCPAP therapy. Vertical dashed lines delineate equivalence ranges assumed to represent no clinically relevant difference. While none of the differences were statistically significant, the 95% CIs of differences in SF-36 vitality scores, and sleep resistance time extended beyond the equivalence ranges in favor of aCPAP. The meaning of a positive difference is indicated at the right side of each panel.

 
Overall acceptance was not different between CPAP modes (Table 2 ). At the end of the study, all patients wished to continue CPAP therapy. When asked which treatment period they had preferred (before unblinding) 26 patients opted for the period with aCPAP, whereas only four preferred cCPAP (Fisher exact test, p < 0.001).


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  		Table 2.. CPAP Tolerance and Preference*

 
The sleep questionnaire indicated significant differences in noise perception and discomfort from high pressure in favor of aCPAP (Table 1). No differences in sleep quality, side effects from mask and nasal discomfort or symptoms from mouth leak were noted. More relevant side effects requiring interruption of therapy or consultations were absent.

Objective Daytime Vigilance
Sleep resistance improved significantly, independent of CPAP mode. With cCPAP, mean sleep resistance time improved by 8.1 min (SE, 1.7 min), and with aCPAP by 10.9 min (SE, 2.0 min) [p < 0.001 vs baseline; p = NS between groups]. The effect sizes were 0.69 for cCPAP and 0.93 for aCPAP. Although the difference in sleep resistance between the two CPAP modes were not statistically significant (37.2 min with aCPAP vs 34.4 min with cCPAP), equivalence could not be confirmed, since the 95% CI of the difference (– 0.2 to + 5.8 min) extended beyond the predefined range of 4 min in favor of aCPAP (Fig 3). Missed stimuli per minute decreased significantly from baseline by 0.36 (SE, 0.09) with aCPAP and by 0.67 (SE, 0.14) with cCPAP (p = NS).

Nocturnal Respiration, Treatment Pressure, and Compliance
At baseline, mean AHI was 41.1/h (SE, 3.6/h) and mean oxygen desaturation index (ODI) was 29.0 (SE, 4.0). Mean AHI decreased significantly by 35.7/h (SE, 3.2/h) with cCPAP and by 36.5/h (SE, 3.7/h) with aCPAP (p < 0.05 vs baseline; p = NS between CPAP modes). Equivalence of both treatment modes was confirmed with a 95% confidence interval of the difference from – 1.7 to + 3.3, which falls entirely within the range of equivalence of AHI of ± 5/h (Fig 3). The mean ODI was reduced by 25.0/h (SE, 3.5/h) and 24.8/h (SE, 3.8/h), respectively (p < 0.05 vs baseline; p = NS between CPAP modes). Treatment effect size for AHI was 1.82 for cCPAP and 1.86 for aCPAP; corresponding values for ODI were 1.13 and 1.12, respectively. Mean mask pressure during 1 month of therapy was lower with aCPAP. Mean difference was – 1.3 cm H2O (SE, 0.4 cm H2O; 95% CI, – 2.1 to – 0.5 cm H2O; p < 0.05).

Mean nightly CPAP use of 4.8 h (SE, 0.3 h) with cCPAP was similar to that with aCPAP of 5.1 h (SE, 0.3 h) [p = NS; Table 1]. In each group, there was one patient with "nonadherence" (use < 2 h), and there were eight patients in the cCPAP group and eight patients in the aCPAP group with mean nightly use > 6 h.

Discussion

In this double-blind, randomized, controlled trial, 1 month of aCPAP treatment was equivalent to cCPAP in improving major outcomes of sleep apnea therapy, including daytime sleepiness, impaired quality of life, and nocturnal respiratory disturbances. With both treatment modes, a significant and clinically relevant relief of the symptoms of OSAS was achieved. Our results suggest that the algorithm implemented in the aCPAP device performs well in respiratory event detection and automatic mask pressure adjustment, and that this is appreciated by the patients who indicated a clear preference for the aCPAP compared to the cCPAP mode.

The effect sizes achieved in major outcomes with aCPAP and cCPAP therapy of ≥ 1.82 for AHI, ≥ 1.99 for ESS score, and ≥ 0.69 for sleep resistance time compare favorably with previous evaluations of cCPAP (effect sizes ≥ 1.61, ≥ 1.40, and ≥ 0.38, respectively).27 Effect sizes > 0.8 are considered as clinically important.25 Moreover, aCPAP was at least equivalent to cCPAP in improvement of these outcomes (Fig 3). Mean CPAP use of 5.1 h for aCPAP and 4.8 h for cCPAP is comparable to previous studies510 and clearly exceeds a mean use of 3.4 h considered as the lower end of treatment time that provides a clinically significant treatment benefit.28

The 90th pressure percentile titrated during a night of aCPAP adaptation has been taken for cCPAP treatment in accordance to a previous study29 with the ResMed AutoSet device, in which the 90th percentile best approximated manually titrated CPAP pressure. In the comparison we performed in six patients, the 90th pressure percentiles titrated with the ResMed AutoSet and the REMstar Auto showed no significant difference, and the treatment effects on respiratory disturbance and vigilance were similar to those in previous studies.27,28 In one study,30 autoadjusted titration has been shown to represent a valid alternative to standard in-laboratory CPAP titration.

Previous studies have addressed the efficacy of aCPAP devices in home therapy of OSAS over several weeks. A randomized study14 including eight patients treated for 3 weeks with the Morphée autoCPAP device (Pierre Medical; Verrieres le Buisson, France) in automatic mode and eight patients in constant mode revealed a better compliance in the aCPAP group of 6.5 h per night vs 5.1 h per night in the cCPAP group. In 1997, Sériès and Mark13 demonstrated in a small (n = 10) cross-over study a similar AHI when patients were treated with the Morphée aCPAP device compared to manually titrated cCPAP. In a single-blind parallel study, Konermann et al9 found better compliance, sleep quality, and lower treatment pressures with aCPAP with the Horizon machine (De Vilbiss; Somerset, PA) compared to cCPAP. However, no data on daytime vigilance were available for this cohort.9 A similar parallel study31 using the Somnosmart device (Weinmann; Hamburg, Germany) also reported lower treatment pressures and higher preference for aCPAP, but no objective data about daytime vigilance were available either. In a randomized cross-over study,12 44 patients selected according to their requirements for a high therapeutic pressure ≥ 10 cm of H2O were treated with AutoSet T or with manually titrated fixed pressure over 6 weeks each. The AutoSet T (ResMed; North Ryde, Australia) mode was superior in sleep symptom scores, SF-36 vitality, and mental health scores. Moreover, median treatment pressures were lower and adherence per night was significantly better with the autoadjusting device, but objective vigilance was not assessed. In a randomized trial10 of two aCPAP devices vs cCPAP addressing objective and subjective sleepiness, nocturnal breathing disturbances, treatment adherence, and quality of life, no differences between cCPAP and aCPAP by the two tested devices (AutoAdjust LT; DeVilbiss; AutoSet T; ResMed) were found.

Conclusions

This double-blind, randomized, controlled trial compares cCPAP to aCPAP in the home treatment of obstructive sleep apnea. Our investigation adds to the evidence demonstrating equivalent improvements of symptoms and measured sleep resistance by aCPAP using a novel device. We found no advantage of aCPAP regarding major outcome parameters such as objective sleepiness, symptoms, or quality of life, but the majority of patients preferred treatment in the autoadjusting mode. Therefore, aCPAP is a promising alternative to conventional CPAP treatment with fixed mask pressure.

Footnotes

Abbreviations: aCPAP = autoadjusted continuous positive airway pressure; AHI = apnea-hypopnea index; cCPAP = constant continuous positive airway pressure; CI = confidence interval; ESS = Epworth sleepiness scale; NS = not significant; ODI = oxygen desaturation index; OSAS = obstructive sleep apnea syndrome; SF-36 = Short Form-36

The study was supported by MEDELA AG, Switzerland, distributor of Respironics products in Switzerland.

Received for publication May 31, 2005. Accepted for publication September 15, 2005.

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