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From the Sleep Disorders Unit (Drs. Oksenberg, Arons, and Radwan), Loewenstein Hospital Rehabilitation, Raanana, Israel; and the Department of Nephrology (Dr. Silverberg), Tel-Aviv Medical Center, Tel-Aviv, Israel.
Correspondence to: Arie Oksenberg, PhD, Sleep Disorders Unit, Loewenstein Hospital Rehabilitation Center, POB 3 Raanana, Israel; e-mail: psycot3{at}post.tau.ac.il
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Abstract |
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Design: Retrospective analysis.
Setting: Sleep Disorders Unit at Loewenstein Hospital Rehabilitation Center.
Patients: Eighty-three consecutive adult OSA patients who underwent a complete nCPAP titration. From this group, 60 patients who spent at least 30 min in both the supine (Sup) and lateral (Lat) positions and 46 patients who had data on both positions during REM and NREM sleep were included in the analysis.
Results: In
most OSA patients (52; 86.7%), the recommended op-nCPAP was obtained
when the patients slept in the Sup posture. The mean op-nCPAP
was significantly higher in the Sup posture (10.00 ± 2.20 cm
H2O) than it was in the Lat posture (7.61 ± 2.69 cm
H2O). The op-nCPAP was significantly higher in the Sup
position than it was in the Lat position in both REM and NREM sleep, as
well as in the severe BMI group (BMI 
30) and in the less obese
group (BMI < 30). Similarly, in the severe (RDI 40) and less
severe groups (RDI < 40), as well as in both age groups (< and
> 60 years of age), the op-nCPAP was significantly higher in the Sup
posture than it was in the Lat posture. Irrespective of the four
parameters mentioned, the actual differences in op-nCPAP between the
two body postures were almost identical, ranging between 2.31 and 2.66
cm H2O.
Conclusions: For most OSA patients, the op-nCPAP level is significantly higher in the Sup position than it is in the Lat position. This is true for REM and NREM sleep, for obese and nonobese patients, for patients with different degrees of severity, and for young and old OSA patients. Since the op-nCPAP was highest in the Sup posture during REM sleep, no nCPAP titration should be considered complete without the patient having slept in the Sup posture during REM sleep.
Key Words: body posture • continuous positive airway pressure titration • obstructive sleep apnea • optimal continuous positive airway pressure • sleep position
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The aim of this study was to estimate the impact that body position has on the titration of the optimal nCPAP (op-nCPAP) for the successful treatment of OSA patients and to evaluate how rapid eye movements (REM) and non-REM (NREM) sleep, body mass index (BMI), RDI, and age are related to the relationship between op-nCPAP and body posture during sleep.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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20)
and agreed to undergo an nCPAP titration test. The data on 83 consecutive OSA patients who underwent a complete nCPAP titration evaluation in our Sleep Disorders Unit between March 1991 and March 1994 were assessed. The titration nCPAP test was usually performed the night following the diagnostic PSG evaluation, but in some cases, the test was performed within 1 or 2 weeks after the diagnostic evaluation. The group included only six female OSA patients. In the total group, the mean ± SD for age was 53.08 ± 10.6 years, for BMI was 33.01 ± 5.59, and for RDI was 62.5 ± 23.3.
PSG Recordings
The patients arrived at the sleep unit around 8:00
PM, and the PSG recordings usually began between 10:00
PM and midnight. The PSG recordings were carried out using
polygraphs (Nihon Koden 4321 and 4414; Nihon Koden; Tokyo,
Japan) and included the parameters that have been detailed
elsewhere.6
The recordings were carried out at a paper
speed of 10 mm/s, and sleep stages were scored according to the
standard.9
Changes in body position were marked in the polygraph and in a chart recorder by the PSG technician who followed the patient's behavior through a closed-circuit TV monitor.
Apnea was defined as an episode of complete breathing cessation of
10 s. Hypopneas were considered as such if a partial breathing
cessation (> 20% reduction in oral/nasal airflow compared with the
level of the previous five breaths) occurred accompanied either by a
drop of arterial oxygen saturation of at least 3% or by an arousal
event. The apnea index and the RDI were calculated as the number of
apneas per sleep hour and the number of apneas plus hypopneas per sleep
hour, respectively. Arousals were scored according to accepted
definitions.10
The CPAP system (Companion 318 unit; Puritan-Bennet; Lenexa, KS) used during the titration test was designed for clinical use, and it had a remote control unit connected to the polygraph. All of the op-nCPAP values are expressed in centimeters of H2O.
CPAP Titration Protocol
During the patients' initial interview, they received the first
explanation about the way the CPAP machine works and about the pros and
cons of this type of treatment. Additional information about CPAP was
provided during the summary meeting in which the patients received a
detailed explanation of the results of the diagnostic PSG evaluation.
Before beginning the nCPAP titration test, the PSG technician showed
the patient the CPAP unit and the different types of masks available
and explained how the mask with the headgear would be fitted. In
addition, an adaptation trial of about 15 to 20 min was carried out
with the CPAP unit running while the patient was sitting awake and
relaxed. This procedure was always carried out in order to allow the
patients to understand the way the system works and to adjust to it
more easily.
The op-nCPAP level was defined as the minimal pressure that overcame apneas, hypopneas, and the arousals related to these breathing abnormalities, as well as the stabilizing arterial oxygen saturation levels. The op-nCPAP overcame snoring in most of the cases, but in some cases, a light snoring sound was heard. The op-nCPAP was titrated for the Sup and Lat body positions and in the different sleep stages. The op-nCPAP was defined as the minimum pressure that eliminated the above mentioned breathing abnormalities and that, by decreasing it, caused the reappearance of some of these breathing abnormalities.
Data Analysis
The comparison of op-nCPAP values between the Sup and Lat
postures according to REM and NREM sleep, BMI, RDI, and age was carried
out by using a simple or two-tailed paired Student's t
test. For the comparison between different BMI categories, analysis of
variance (ANOVA) for unweighted means was used. Differences between the
means were tested by using Scheffe's post hoc test. All of
the values are expressed as mean ± SD. A p value < 0.05 was
considered significant. Data analysis was performed by using a
statistical package (SAS Version 6.12; SAS Institute; Cary, NC).
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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As seen in Figure 1 , in most of the 60 OSA patients (86.7%), the op-nCPAP levels were obtained when the patients slept in the Sup posture. In five patients (8.3%), the op-nCPAP level was the same in both postures, and in only three patients (5.0%), the op-CPAP level was higher in the Lat position.
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The effect of REM and NREM on op-nCPAP in these patients is shown in Table 1 . The op-nCPAP was significantly higher in the Sup posture than it was in the Lat posture in both REM (t = 9.90; p < 0.0001) and NREM (t = 10.06; p < 0.0001) sleep. In addition, the op-nCPAP was significantly higher in REM sleep than it was in NREM sleep in both the Sup (t = 5.69; p < 0.0001) and Lat positions (t = 5.36; p < 0.0001). Thus, the sequence from highest to lowest op-nCPAP values was as follows: Sup REM > Sup NREM > Lat REM > Lat NREM.
The effect of BMI on op-nCPAP is also seen in Table 1
and Figure 2 . In Table 1
, it can be seen that the op-nCPAP was significantly higher
in the Sup position than it was in the Lat position in both the obese
group (BMI 30; N = 39; t = 8.14; p < 0.0001) and the
nonobese group (BMI < 30; N = 20; t = 6.24; p < 0.0001). Also,
the op-nCPAP level was significantly higher in the obese group than it
was in the nonobese group in both the Sup (t = 2.94; p < 0.0047)
and Lat (t = 2.63; p < 0.010) positions. Thus, the sequence from
highest to lowest op-nCPAP values was as follows: Sup obese > Sup
nonobese > Lat obese > Lat nonobese. When the group was
divided into four BMI categories (Fig 2)
(1. BMI 
30, N = 20; 2.
BMI, 30 to 34.9, N = 19; 3. BMI, 35 to 39.9, N = 14; and 4. BMI
> 40, N = 6), it was found that as BMI increased, the op-nCPAP also
increased significantly for the Sup posture (ANOVA,
F3,55 = 5.73; p < 0.0017) and for the Lat
posture (ANOVA, F3,55 = 6.07; p < 0.001),
but the differences between the means (Scheffe's post hoctest) were significant in the Sup posture only between
categories 1 and 4 (p < 0.05) and in the Lat posture between
categories 1, 2, and 3 and category 4 (p < 0.05). For the three less
severe BMI categories (categories 1, 2, and 3), the op-nCPAP was
significantly higher in the Sup position than it was in the Lat
position (t = 6.24, p < 0.0001; t = 6.27, p < 0.0001; and
t = 5.24, p < 0.0002, respectively). The difference in op-nCPAP
between Sup and Lat positions in the most severe BMI category was not
statistically significant (t = 2.39; p < 0.062). The effect of RDI
is also seen in Table 1
. For the RDI 40 group (N = 47), as well
as for the RDI < 40 group (N = 12), the op-nCPAP values were
significantly higher in the Sup position (t = 8.63; p < 0.0001)
than they were in the Lat position (t = 6.27; p < 0.0001).
However, in the group with severe RDI (RDI 40) compared to the less
severe group (RDI < 40), the op-nCPAP was significantly higher
(t = 2.61; p < 0.013) only for the Sup posture.
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60 years old (N = 18) and patients
< 60 years old (N = 42). It is noteworthy that irrespective of the four parameters studied, the actual differences in op-nCPAP between the two body postures were almost identical, ranging between 2.31 and 2.66 cm H2O.
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Our results are not surprising, however, since the detrimental effect of the Sup posture on the incidence and severity of breathing abnormalities during sleep has been well described.1 In addition, the results of this study provide more evidence that shows that there is a greater upper airway resistance11 12 and greater tendency for the upper airway to collapse13 14 in the Sup position than there is in the Lat position during sleep.
We found that the op-nCPAP was higher in the Sup position in both REM and NREM sleep, and it presents the following sequence: Sup REM > Sup NREM > Lat REM > Lat NREM. These data confirm the data of Issa and Sullivan.13 This effect is probably due to the marked atonia characterizing REM sleep, which results in an increased upper airway resistance.
Patients with higher BMIs, as well as those with higher RDIs, require higher op-nCPAP values to eliminate their breathing abnormalities than the less severe ones do, but here again, the Sup position played a dominant role. Similar data have been obtained by others.15 No differences in op-nCPAP were seen in OSA patients who were < or > 60 years of age, but as for BMI and RDI, in both groups of patients the op-nCPAP was higher in the Sup position than it was in the Lat position. Thus, irrespective of the BMI, RDI, and age, in order to recommend an adequate op-nCPAP, the nCPAP titration test must include the evaluation of the patient in the Sup position and during REM sleep.
The significant differences between the op-nCPAP in the Lat vs the Sup position, together with the differences in the op-nCPAP needed to overcome the breathing abnormalities during REM vs NREM sleep, could be used as a strong argument for the use of "smart" CPAP machines, which adapt the pressure according to the different needs of the OSA patients.16
Only a few articles have investigated the effect of body position on op-nCPAP.
Pevernagie and Shepard,17 in a retrospective study of 100 OSA patients, compared the op-nCPAP (which they defined as the pressure that eliminated sleep-disordered breathing events and snoring in the Sup position) in 79 patients. Forty-nine PP (62%) had a lower op-nCPAP (8.0 ± 2.2) than the 30 NPP (38%; 9.1 ± 1.8). This difference between PP and NPP was significant but small. This small difference is not surprising since the RDI in the back posture was similar for both groups of patients, and by definition, the op-nCPAP level was that pressure that overcame the breathing abnormalities in the Sup posture. Unfortunately, not enough data were available for the comparison of the op-nCPAP in the Lat posture.
Neill et al14 compared the upper airway closing pressure (UACP), which is the mean of the minimum pressures generated in the last two breaths before an arousal occurred in a nasal occlusion test, and the upper airway opening pressure (UAOP), which is the minimal CPAP required to prevent apneas and hypopneas, in eight obese males with severe OSA in three postures (Sup, Sup elevated to 30°, and Lat) during NREM sleep. They found that the upper airway became less collapsible (reduced UACP) and easier to open (reduced UAOP) in the 30° elevated posture compared with the Sup sleep posture. Compared to the Sup posture, the Lat posture had a similar UACP but did allow the upper airway to open more easily (reduced UAOP). Both the elevation and Lat positioning produced a reduction of about 50% in the therapeutic CPAP pressure compared to the Sup posture. The eight patients in this study were obese and had severe OSA, and six were found to be nonpositional. It would be interesting to carry out a similar study that uses the same protocol but investigates only positional OSA patients. It would be expected that in this population, the adoption of the Lat posture would demonstrate a significant improvement in UACP. This study and the previous one from the same group18 showed that adopting the reclining sitting position produced a significant improvement of breathing function during sleep. These studies demonstrate again that changes in body posture during sleep have important therapeutic implications for patients with breathing disorders.
Issa and Sullivan13 described three OSA patients in whom the UACP was significantly lower in the Sup posture compared to the Lat position in all sleep stages. Although details of the weight and severity of these patients was not provided, it appears that they were less obese than the patients of Neill et al.14 As a result, it is probable that they were positional OSA patients, which would explain the differences in the results.
One limitation of our study is that during the nCPAP titration test, we did not monitor upper airway resistance, and it is probable that if an oesophageal pressure sensor were used, the op-nCPAP values would have been a little different. Also, recent data have shown that after the disappearance of arousal caused by apneas, hypopneas, and snoring, there is still high negative intrathoracic pressure with limited inspiratory flow. Thus, if the end point of an adequate nCPAP titration is to reach a normal oesophageal pressure or the normal contour shape of the inspiratory flow, higher CPAP pressures will probably be needed.19 20 Nevertheless, in the present study, the same protocol was used for all of the OSA patients investigated so that the differences observed for op-nCPAP between the Sup and Lat postures and the effects of REM and NREM sleep, BMI, RDI, and age on the patients were independent of this mentioned limitation.
We recently6 demonstrated in a large population of OSA patients that PP represent more than one half of the patients who received OSA diagnoses in our Sleep Disorders Unit. These OSA patients have, in most of the cases, a mild to moderate form of the disease since they have the Lat posture for sleep, in which the number of breathing abnormalities is significantly much less than it is in the Sup posture. However, the critical issue is that the severity of the disease of these PP is markedly related to the amount of sleep spent or not spent in the Sup position. Sometimes a total absence of these breathing disturbances are observed in the Lat posture, and for those cases and those patients who have an RDI < 10 in the Lat posture, avoiding the Sup position during sleep (positional therapy) represents a valuable and effective form of therapy.
In addition, we showed21 in a group of 13 positional OSA patients that avoiding the Sup position during sleep for 1 month caused a significant reduction in 24 h BP values in hypertensive and normotensive patients. Based on these results, we argue that since about 30 to 40% of all essential hypertensive patients have OSA, and since more than one half of OSA patients are positional, avoiding the Sup position during sleep could, if verified by larger studies, become a new nonpharmacologic treatment for many hypertensive patients. The results of the previous studies, together with the results obtained in the present study, clearly demonstrate the detrimental impact that the Sup posture has on breathing function during sleep. It is not completely clear by which mechanism the Sup posture produces a deleterious effect on the upper airway during sleep, but most of the evidence reported up to now suggests that the gravitational factor is the most dominant element responsible for this effect.22 However, it is still not clear what the relative contribution of anatomic and physiologic components is to this effect. Further data on the effect of the Sup posture on breathing function during sleep have been recently reviewed.23
In summary, this study has shown that, for most of the OSA patients who underwent a nCPAP titration evaluation, the recommended op-nCPAP was obtained during sleep in the Sup posture. The mean op-nCPAP for the Sup posture was significantly higher than that for the Lat posture. The op-nCPAP was higher in the Sup posture in both REM and NREM sleep. OSA patients with a higher BMI required higher op-nCPAP, but for both obese and nonobese OSA patients, the op-nCPAP was higher in the Sup posture. The op-nCPAP was higher in the most severe RDI group compared with the less severe RDI group but again, for both groups, the op-nCPAP values were higher in the Sup position than they were in the Lat position. OSA patients < and > 60 years of age had similar op-nCPAP, but in both groups, the op-nCPAP was higher in the Sup posture than it was in the Lat posture.
These results demonstrate that body position has a profound effect, not only on the occurrence and severity of breathing abnormalities during sleep, but also on the adequate titration of the op-nCPAP. Since OSA patients may change their body posture several times during the night, these results also support the use of "smart" CPAP machines, which have the capability to adapt the op-nCPAP to the needs of the patient.
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Acknowledgements |
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Footnotes |
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Received for publication November 3, 1998. Accepted for publication May 5, 1999.
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