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* From the Pneumology Department, Klinik Ambrock, Hagen, Germany.
Correspondence to: Georg Nilius, MD, Klinik Ambrock, Ambrocker Weg 60 58091, Hagen, Germany; e-mail: nilius{at}klinik-ambrock.de
Abstract
Objectives: To compare polysomnographic data and compliance in sleep apnea patients receiving continuous positive airway pressure (CPAP) and pressure-relief CPAP (PRCPAP) [C-flex; Respironics; Murrysville, PA] as first treatment in the sleep laboratory and subsequently at home.
Design: A prospective, randomized, crossover design was used in the sleep laboratory, and a prospective randomized design was used at home.
Patients: Data were collected from 52 sleep apnea patients for whom CPAP was used for the first time.
Interventions: Treatment with constant CPAP and PRCPAP.
Measurements and results: Patients with a first-time diagnosis of obstructive sleep apnea syndrome (OSAS) underwent conventional CPAP titration. Thereafter, polysomnography was performed at the titrated pressure using both the fixed CPAP pressure mode and the PRCPAP mode in a randomized crossover approach. The patients were then discharged home for 7 weeks of treatment with the last-applied treatment mode, and compliance data were established at the end of that time. The average apnea-hypopnea index was 53.3/h in the "diagnostic night," 5.8/h with CPAP, and 7.0/h with PRCPAP. The native arousal index was 35.2/h, 12.6/h with CPAP, and 12.9/h with PRCPAP (not significant [NS]). The central apnea index was 0.7/h with CPAP and 1.2/h with PRCPAP (p < 0.05). Compliance after 7 weeks was, on average, 9.4 min longer with PRCPAP than with CPAP (NS). Evaluation of a 13-item questionnaire showed scores of 16.4 for PRCPAP and 18.1 for constant CPAP (NS) [the fewer the complaints, the lower the score]. With regard to oral dryness, the score with PRCPAP (1.4) was significantly lower than with constant CPAP (1.9) [p < 0.05]. This difference was no longer detectable after 7 weeks.
Conclusion: In terms of the effectiveness in treating obstructive sleep apnea, PRCPAP and constant CPAP are comparable. During the first night of treatment, patients receiving PRCPAP had less dryness of mouth; over a period of 7 weeks, this difference disappeared. Nightly use of the device was comparable in both groups. PRCPAP is therefore a new ventilation mode that enables effective treatment of OSAS patients. Further studies should be done to investigate the effects of expiratory pressure lowering in low-compliance patients and patients requiring CPAP > 9 cm H2O or experiencing dry mouth with CPAP.
Key Words: compliance • continuous positive airway pressure • obstructive sleep apnea • pressure relief continuous positive airway pressure
Continuous positive airway pressure (CPAP) is the therapy of choice for the treatment of OSAS. Although CPAP is effective treatment of objective and subjective complaints,12 acceptance expressed as duration of nocturnal use is only from 3.9 h3 to 6.5 h45 per night over the long term. Many patients receiving CPAP complain of dry nose and throat.6789 The application of airway humidification ameliorates this problem and improves the compliance rate.10 A further step in the development of the CPAP devices was the modification of the airway pressure pattern. Automated CPAP devices measure airway obstruction and lower the pressure as necessary.2111213141516171819
One strategy aimed at reducing the pressure applied was the introduction of a bilevel device capable of varying inspiratory and expiratory levels.202122 Neither automatic CPAP nor bilevel positive airway pressure have substantially improved long-term compliance.23
The main problem with obstructive sleep apnea syndrome (OSAS) is narrowing of the upper airways during inspiration. Positive airway pressure at the beginning of expiration is not necessary because the risk of collapse is reduced during this part of the respiratory cycle.
A new CPAP device (C-flex; Respironics; Murrysville, PA), termed pressure-relief CPAP (PRCPAP), that differs from conventional CPAP in the lowering of the pressure at the onset of expiration is now available. The magnitude of the reduction in pressure depends on the expiratory flow and can be preset in three different steps. The reduction of pressure at the beginning of expiration is intended to reduce the sensation of breathing against high pressure without causing the upper airways to collapse.
In this prospective randomized study comparing PRCPAP at setting 3 (the level of greatest pressure reduction during expiration) with constant CPAP, we aimed to investigate the efficacy of the new device in reducing respiratory events and arousals in patients with newly diagnosed OSAS. We hypothesized that patients receiving PRCPAP would show better compliance (measured as objective CPAP usage) over a period of 7 weeks.
Materials and Methods
The study was approved by the Ethics Commission of the University of Witten/Herdecke, and all the patients gave written consent to participate. One patient withdrew consent immediately prior to discharge from the sleep laboratory.
Fifty-two patients with suspected OSAS who were referred to a university sleep laboratory by pneumologists and general practitioners were recruited (46 men and 6 women; mean age ± SD, 56.9 ± 9.4 years; mean body mass index, 32.7 ± 5.5 kg/m2; mean height, 174.4 ± 6.9 cm; mean weight, 92.2 ± 17.2 kg). All patients underwent polysomnography for the first time. OSAS was diagnosed when the apnea-hypopnea index (AHI) was > 20/h. Exclusion criteria were an inability to follow instructions, failure to give informed consent, acute infection, acute cardiac disease such as acute coronary artery syndrome, New York Heart Association grade 3 or 4 heart failure, and acute pulmonary thromboembolism.
Study Design
After evaluating daytime sleepiness with the Epworth sleepiness scale (ESS)24 and performing diagnostic polysomnography, the patients participated in our standard daytime CPAP training program. After choosing between several nasal interfaces (nasal or nasal/mouth masks from different manufacturers), the patients underwent a daytime CPAP training session of 4 h at a constant pressure of 4 cm H2O. On the following night in the sleep laboratory, manual CPAP titration was performed by increasing the pressure from 6 cm H2O in hourly incremental steps of 1 cm H2O up to 12 cm H2O. The lowest effective pressure was chosen for the CPAP treatment session in the sleep laboratory the following night, and for subsequent treatment at home, during which the AHI was < 5/h, and snoring and respiratory-related arousals were abolished.
On the next 2 laboratory nights, the effects of constant CPAP or PRCPAP at pressure-reduction setting 3 were studied in randomized order using polysomnography. Each morning, the patients were asked to complete a questionnaire; after the second night, the patients were sent home with the device set to the program of the previous night. At the end of week 7, the patients were visited at home by a technician. Compliance was assessed by reading the usage time shown on the integrated clock, and the patients were asked to complete the above-mentioned questionnaire. The technician had no information from the investigators about the modality that the patients were receiving. Nevertheless, it was not possible to blind the technician totally because information about the mode used was written in the memory function of the CPAP machine.
The physician (A.H.) and technicians reviewing the polysomnographic data and performing the manual CPAP titration were blinded to the treatment mode employed. Only the person (F.D.) responsible for randomization had knowledge of the order of the treatment modes in the individual patient, and he also set the devices to the respective mode. The patients were informed that they would receive two different modes of treatment involving different forms of pressure application but were given no further details. Since the devices used appeared identical, patients were unaware of the mode actually applied.
After 7 weeks, each patient was visited at home by a technician. The internal storage of the device was accessed to obtain information on compliance during treatment (Fig 1 ).
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The polysomnographic recordings were scored manually by one experienced observer (A.H.). Sleep stages and arousals were analyzed in accordance with the criteria of Rechtschaffen and Kales25 and the American Sleep Disorders Association.26 Arousals were defined as respiration induced when they occurred at the earliest with the onset of, at the latest 2 s after, an apnea or hypopnea. If two or more snoring signals occurred in a sleep period of 30 s, this period was registered as a snoring period.
Obstructive apnea was defined as a reduction in respiratory flow of at least 20% compared with baseline and lasting at least 10 s despite ongoing respiratory effort. Hypopnea was defined as a reduction in airflow of at least 50% compared with baseline that lasted at least 10 s.
The patients completed a questionnaire after each treatment night with PRCPAP and constant CPAP in the sleep laboratory and after 7 weeks of treatment at home. Each item was scored on a 5-step scale ranging from 0 (very good) to 5 (very poor).
Sleepiness
Subjective sleepiness was evaluated by using the Epworth sleepiness scale (ESS).24 The self-reporting questionnaire is shown in Figure 2
. The questionnaire was an in-house instrument and had not previously been validated. The items were oriented to the most important side effects observed with CPAP treatment6 and took account of the possible effects of pressure lowering with PRCPAP.
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Results
Following history taking, physical examination, and diagnostic polysomnography, 52 patients gave informed consent to participate in the study. One patient withdrew his previously given consent immediately prior to being discharged home. Twenty-six patients were randomly assigned to constant CPAP, and 25 patients were assigned to PRCPAP. There were no significant differences between the two groups in any of the anthropometric data (statistical data not shown).
Polysomnographic Data From the Diagnostic Polysomnography
Mean total sleep time (TST) for all 52 patients was 307.2 ± 58.9 min. Mean percentage of stage S1 sleep was 13.3 ± 9.7%, mean percentage of S2 sleep was 61.5 ± 11.3%, mean percentage of S3/4 sleep was 12.6 ± 9.5%, and mean percentage of rapid eye movement (REM) sleep was 12.8 ± 7.2%. Mean arousal index was 35.2 ± 21.5/h. Mean central apnea index was 2.8 ± 4.3/h, mean obstructive apnea index was 22.2 ± 18.5/h, and mean mixed apnea index was 4.8 ± 7.8/h. An overall mean of 23.5 ± 10.4 hypopneas per hour was noted. Total AHI was 53.3 ± 21.2/h, and mean minimal oxygen saturation was 76.3 ± 10.2%.
There was a statistically significant difference in TST between the two subgroups treated with PRCPAP or constant CPAP at home, but no significant differences were observed for any other polysomnographic parameters (data not shown). Table 1 shows polysomnographic data comparing constant CPAP with PRCPAP on the first night of CPAP therapy.
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Snoring decreased from 68.6 ± 31.69/h at baseline to 12.1 ± 21.9/h with PRCPAP (p < 0.0001) and 10.7 ± 20.6/h with constant CPAP (p < 0.0001). The total number of arousals decreased significantly from 35.2 ± 21.5/h to 12.9 ± 8.6/h with PRCPAP (p < 0.0001) and 11.6 ± 5.7/h with constant CPAP (p < 0.0001). The difference between the two modes was not significant (p = 0.33), and both were associated with a significant improvement in REM (p < 0.001) and S3/4 sleep (p < 0.001).
Both modes brought about an improvement in daytime sleepiness. The ESS score decreased from 10.9 at baseline to 5.8 after 7 weeks of treatment with PRCPAP, and from 10.2 at baseline to 6.1 with constant CPAP (the difference between CPAP and PRCPAP was not significant [NS], p = 0.83). The results of manual pressure titration show a mean pressure of 8.7 ± 1.3 cm H2O for the 26 patients sent home with constant CPAP and 9.0 ± 1.7 cm H2O for the 25 patients receiving PRCPAP.
After 7 weeks of therapy, the patients in the constant CPAP group used the device 5.2 h per night; patients in the PRCPAP group used the device 5.3 h per night. The difference of 9.4 min per night was not statistically significant (p = 0.99).
We additionally analyzed patients needing a pressure 
9 cm H2O. Manual CPAP titration identified 25 patients in need of such a pressure (13 patients receiving PRCPAP and 12 patients receiving constant CPAP). In this subgroup, the nightly duration of use was 5.6 h in the PRCPAP group and 5.3 h in the constant CPAP group; the difference of 18.6 min between the two groups was not statistically significant (p = 0.79).
Results of the Questionnaire
Only 45 patients completed the entire questionnaire, and only the data for these patients were considered in the final analysis. The total side effects score after the first night was 16.4 in the PRCPAP group and 18.1 for the constant CPAP group (NS). Among the side effects reported, only dryness of mouth showed a statistically significant difference: in the PRCPAP group, the patients scored a mean of 1.4 points for this side effect after the first night, compared with 1.9 points (p < 0.05) in the constant CPAP group.
After 7 weeks of treatment at home, the total score in the PRCPAP group was 15.5 (23 patients) and in the constant CPAP group was 16.5 (22 patients) [difference not statistically significant]. An analysis of the individual questions after 7 weeks revealed no statistically significant difference between the groups for any item.
Discussion
PRCPAP (C-flex; Respironics) is a new CPAP option that lowers the pressure at the start of expiration. The results of this study confirm that both therapy modes are equally effective in terms of respiratory parameters and sleep profile. With PRCPAP in the sleep laboratory, the overall group had a mean of 1.2 ± 2.5 central apneas per hour, compared with 0.7 ± 1.0/h with CPAP. Although statistically significant, this difference has no clinical relevance.
The definition of hypopnea we applied was that generally accepted, namely a reduction in flow of > 50% compared with baseline. With both devices, we recorded this flow with an attached analog output module, and also measured the flow at the mask with a flow-pressure monitor. This enabled the detection of small reductions in the flow signal. The data revealed no significant difference between constant CPAP and PRCPAP in terms of obstructive apneas and hypopneas, but there was a small increase in AHI from 5.8/h with constant CPAP to 7.0/h with PRCPAP. This difference is of no clinical significance. On the basis of our results, we conclude that in terms of the polysomnographic data, PRCPAP at pressure-reduction setting 3 is comparable with constant CPAP for most patients with uncomplicated OSAS. The clinical benefit of treatment (reduction in sleepiness) is identical with both devices.
Data on compliance, and the ESS score were collected for both devices after 7 weeks of treatment. The mean usage of 5.3 h in the PRCPAP group and 5.2 h in the constant CPAP group was within the usual range reported in the literature. The difference (9.4 min) between the two groups was not significant. A subgroup of patients on a set pressure of 9 cm H2O revealed a difference between the two modes of 18.6 min. Approximately 20% of all patients receiving CPAP reported in the literature complained of a sensation of exhaling against a high pressure.6 It is possible that the pressure reduction during expiration on PRCPAP is more comfortable for those patients who need a higher CPAP pressure. Further studies in this subgroup of patients are needed to clarify this point. A shortcoming of the present study was the decision to treat the patients at home with either constant CPAP or PRCPAP; a crossover design would have had greater statistical power for detecting differences between the two groups.
The results of the questionnaire show no significant difference between PRCPAP and CPAP with regard to the overall score, either after the first night or after 7 weeks. Most interestingly, dryness of mouth was less pronounced with PRCPAP than with CPAP. It is therefore conceivable that PRCPAP offers relief to patients with side effects due to mouth breathing during the accommodation period. However, the effect is no longer to be seen at follow-up after 7 weeks.
The aim of various modifications of the CPAP mode has been to improve compliance. To date, it has not be shown that compliance, measured as the nightly duration of use of the machine, can be improved by using different forms of pressure application, such as bilevel ventilation or by automated CPAP machines.16212223272829 The reason for this is that the extent of possible side effects is mostly independent of the level of pressure used during CPAP.14 Another factor may be humidification, but the results obtained so far have been controversial. While the use of a humidifier cannot routinely be recommended, humidification may indeed reduce the side effects attributable to the upper airways.103031
Compliance is influenced by a number of different factors independent of the pressure mode employed. Such psychosocial factors as living alone,32 major life events32 in the recent past, high anxiety or depression scores,33 or unfavorable coping strategies34 have an influence on the use of CPAP. Patients with a higher apnea/hypopnea score have a better CPAP compliance,35 and the quality of sleep during the first night predicts subsequent compliance.35
Compliance can be improved by group work with the patients36 or by intensive support at the start of CPAP therapy.3 In contrast, less intensive support at the beginning may reduce CPAP usage.37
It must be noted that the patient group investigated here was receiving CPAP treatment for the first time, and all patients underwent the same education program. In this group with an average AHI of approximately 53/h, reduced compliance was not to be expected, and this was confirmed by the average use of the device—> 5 h each night—in both treatment modes. Compared with the results published in the literature,345 compliance was quite high in both groups. The potential advantages of expiratory pressure lowering could therefore not have played any particular role in this group. Accordingly, these data cannot simply be used to draw conclusions about patients with problems and thus low compliance. We propose that further studies be done to investigate the effects of expiratory pressure lowering in low-compliance patients. Patients requiring a CPAP pressure > 9 cm H2O and experiencing dry mouth with CPAP also need to be studied.
Footnotes
Abbreviations: AHI = apnea-hypopnea index; CPAP = continuous positive airway pressure; ESS = Epworth sleepiness scale; NS = not significant; OSAS = obstructive sleep apnea syndrome; PRCPAP = pressure-relief continuous positive airway pressure; REM = rapid eye movement; TST = total sleep time
This study was financed by a gift from Heinen U. Lowenstein.
Dr. Ruhle has received research funding from Fisher A. Paykel, Heinen U. Lowenstein, ResMed, and Weinmann, but this funding has gone into department funds.
Dr. Nilius, Andreas Happel, and Ulrike Domanski have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article
Received for publication April 6, 2005. Accepted for publication March 9, 2006.
References
This article has been cited by other articles:
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  A. Ozsancak, C. D'Ambrosio, and N. S. Hill Nocturnal Noninvasive Ventilation Chest, May 1, 2008; 133(5): 1275 - 1286. [Abstract] [Full Text] [PDF]
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