Discussion
This study provides additional clinically relevant information to the previous validation study of a forehead PT device.21 The results show that the use hours, the percentage of nights used per week and the percentage of patients with good compliance were similar in both groups during the follow-up period. As expected, the percentage of time in the supine position was significantly lower in the AD group than in the ID group. No relevant side effects were reported, and patient satisfaction was high in both groups.
The median daily use of the device was higher than 6.5 hours/day in both groups, which is equivalent to other published studies with similar AD,8 17 19 22–27 where the mean/median daily use ranged from 7.6 hours/night at a month26 to 5.2 hours/night at 12 months.20 The fact that daily use was almost equivalent between the ID and AD patient groups provides confirmation that the device vibration was well tolerated and did not hamper the routine use of the device. These results are in line with our previous publication in which no differences in arousal index or sleep efficiency were observed between both groups during PSG at the end of the follow-up period.21
As expected, our forehead device was able to significantly reduce the time patients spent with their heads in the supine position in the AD group. This is in agreement with our previous publication,21 in which the AD group had a greater and significant reduction in the AHI and time in the supine position measured at the chest compared with the ID group, thus suggesting that applying the vibration at the forehead could be effective in changing both head and body position. Our results are not directly comparable to those of other studies, since all of them provide data on body position measured at the chest by PSG and not at the forehead. However, they reported similar reductions in the percentage of time in the supine position measured at the chest,13 17 24 28–30 although many of them had values higher than our results.1 9 19 20 23 25–27 31
The time spent in the supine position measured by the device at the forehead in the ID group (median 12.4%) was low compared with the value measured at the chest by PSG in our previous publication (mean 43.7%).21 Although not directly comparable, our findings are in line with the results of van Kesteren et al,32 who reported an overall 23% reduction in mean time spent with their heads in the supine position compared with their trunks in the supine position, but their heads turned sideways. Additionally, this reduction increased to approximately 55% in those patients in whom head placement in the supine position aggravated the severity of OSA.32 The reduction in time spent with patients' heads in the supine position compared with their trunks could be explained by a placebo effect, since the simple fact of placing the device on the forehead could induce the patients to modify their head position.
Likewise, it is necessary to highlight the role that head position plays in the reduction in the AHI, as has been shown in other studies2 32 33 in which an overall reduction between −5 and −10 events/hour in the AHI is observed when only the head is in lateral position. This reduction can be of a greater magnitude in less obese patients,2 such as POSA patients.3 Consequently, applying the stimulus at the head can provide beneficial effects, allowing a greater freedom of movement for patients to adopt different positions during sleep (especially for women who sleep more in the supine position).32 34 This could be very useful in the management of POSA patients who also suffer from musculoskeletal problems, especially shoulder and back pain, which has been reported as an adverse effect in other studies.17 28
Other devices that apply a vibration stimulus on the chest are designed to allow a training phase of 10 nights, in which the vibration activity increases progressively to gradually train the patient in avoiding the supine sleep position19 26 28; however, no data on the effect during the first nights have been previously reported. Our day-by-day analysis of the use time during the first 2 weeks of treatment revealed that patients in both the ID and AD groups used the device during the same time from the first day and that the use time was maintained relatively constant during the first 2 weeks and throughout the follow-up period. A similar behaviour was observed when analysing the percentage of time in the supine position on a daily basis; a reduced percentage of supine sleep in the AD group was also achieved from the beginning and with small variations during the follow-up period. These findings suggest that the therapeutic effect is obtained from the first night and that no training period is necessary. The earlier effect of the device avoids having patients undertreated during some days and is important for achieving a prompt reduction of symptoms.
Patients in both groups used the device the same percentage of days per week during the whole follow-up period (85.7%), which is in agreement with other studies ranging between 100% at a month13 17 and 69% at a year8 and suggests that the treatment is well tolerated at mid-term.
In this study, we analysed two different criteria for compliance. First, good compliance was defined as ≥4 hours/night and ≥70% of nights as CPAP criteria.5 We obtained high compliance rates in both groups, similar to other studies evaluated between 1 and 12 months of follow-up.8 17 19 25 31 Considering that when this criterion is applied to PT, it provides compliance rates higher than usual values for CPAP,6 it can be speculated that a more restrictive criterion could be more suitable in positional treatment for encouraging patients to adhere to therapy. Additionally, it has been reported that the effectiveness of treatment is directly related to the amount of therapy used.35 36 When considering ‘optimal’ compliance, we obtained compliance rates at 3 months with AD higher than values reported for CPAP at the same follow-up period.36 37 Other studies on PT have also used this criterion, although with lower compliance rates.24 This ‘optimal’ compliance criterion is in line with other studies that suggest that CPAP use of 5 hours/night is necessary to restore sleepiness to normal levels.35 36
Patients were satisfied with the device, rating all the studied items with values of 8.5 or higher over 10 in both groups. This positive evaluation is supported by the high daily use and the percentage of compliant patients compared with CPAP treatment.8 9 Other studies have shown similar positive patient satisfaction.25
No major side effects that required interruption of treatment were recorded. Minor side effects were described, being the most reported in both groups; frequent awakenings were significantly higher in the AD group (60%), although half of them reported this side effect less than once per week. This value is in line with other studies on similar devices reporting awakening rates between 61% and 78%,1 9 although higher than others.20 This could be explained by the intended effect of the vibratory stimulus for inducing a body position change that might be subjectively perceived, as reported in other studies.1 22 23 25 However, these awakenings did not translate into a worsening in subjective evaluation of device by patients (figure 5), in patient compliance (figure 4), or in objective measurements in macro and microstructure of sleep by PSG.21
Although a few patients reported skin irritation in the ID group, none of them required medical intervention, and all completed the study protocol. The differences between the two groups were attributed to chance.
Other side effects were reported occasionally. In other studies, side effects were also reported, such as discomfort, with rates between 17% and 29%,1 20 difficulty initiating sleep in 67%,1 or back or shoulder pain, with incidences ranging from 4% to 33%.1 13 23 25 Since our device allows patients to turn only their heads without turning their bodies, it could be useful for those patients with musculoskeletal problems.
Our study had the limitation of not having a simultaneous recording of the postural device with the sleep study by PSG, which supposes the difficulty of comparing the changes in head position with respect to body. In addition, the lack of consensus regarding the criteria for measuring position changes and their influence on treatment results for PT assumes an additional difficulty when comparing different treatment modalities.