The present study compared OSA index values and the percentage of supine sleep time using RootiRx device in both hospital and home settings. Because patch-type wearable devices cause less interference to individuals’ sleep than do PSG measurements, lower values for parameters such as the CVHRI, CEI, Rx index, and percentage of supine sleep time were noted in the home setting (Table 2 and Fig. 2). Moreover, significant correlations were observed between the variations in the percentage of supine sleep time and the OSA index values (Fig. 3). In other words, greater changes in the sleep time spent in the supine position were correlated with greater changes in the OSA index values. Participants with SE ≥ 90% in hospital also exhibited higher Rx index values and higher percentages of supine sleep time in the hospital setting (Fig. 4). Furthermore, even in patients with SE ≥ 80% and SE ≥ 90% in hospital settings, significant correlations were observed between increased ∆Rx index values and ∆Supine% (Fig. 5), indicating that patch-type wearable devices such as RootiRx may cause less interference to sleeping position than does PSG even when these individuals exhibited high SE in hospital settings. According to our literature review, this is the first study to investigate these correlations between variations in sleeping position and OSA indexes in hospital- and home-based data.
Higher OSA indexes were noted in the hospital than at home, indicating that in-laboratory PSG may overestimate OSA severity. This finding may be partially ascribed to environmental factors, such as the equipment, testing room, and bed, which may hinder changes in sleeping position.
Discrepancies between OSA severity measurements obtained in hospitals and at home have been documented. A study conducted in 1996 centred on the effects of PSG on sleeping position, suggesting that PSG may influence the diagnosis of positional OSA.(24) In that study, 12 patients with positional OSA who had undergone standard PSG returned for 2 additional nights of study without the attachment of PSG leads. The mean percentage of supine sleep time (56%) was greater during the PSG night than during the non-PSG nights. A large-scale retrospective study (2019) on positional OSA treatment with the Sleep Position Trainer, a vibrating device, reported that the PSG apparatus caused an increase in the percentage of supine sleep time and may increase the measured OSA severity.(25) The median AHI decreased from 13.3/h to 10.3/h (P < .001), and 33% of the patients exhibited a change in OSA severity (AHI obtained in hospital settings vs adjusted AHI obtained at home). These outcomes support our findings that PSG measurements may affect sleeping position and increase the percentage of sleep time in the supine position. Therefore, the effects of PSG equipment on sleeping position may lead to higher AHI values, leading to the overestimation of OSA severity.
The significant correlations between the ∆Supine% and differences in OSA indexes, including the ∆CVHRI, ∆CEI, and ∆Rx index, indicated that the increase in the percentage of supine sleep time and the corresponding increase in OSA severity might be a general pattern rather than being limited to specific patient groups. Moreover, this finding has clinical relevance because if sleeping position is influenced by the PSG apparatus and this causes significant overestimation of OSA severity, treatment strategies are likely to be affected.
Some may argue that OSA severity as determined through PSG may be affected by other environmental factors. To address this concern, we analysed the sleep parameters in participants with high SE, in whom the possibility of OSA severity overestimation owing to sleep stage can be largely excluded. Because such patients had long sleep times in the hospital setting, the AHI values obtained from PSG and the OSA index values obtained from the RootiRx were not categorised according to short sleep time. In other words, in patients with high SE, the overestimation of OSA severity is more likely to be attributable to sleeping position than to alterations in total sleep time. Moreover, the ∆Rx index was significantly correlated with the ∆Supine% in the high SE groups. These results suggest that the overestimation of OSA severity in hospitals may be mainly due to patients’ sleeping positions. Therefore, the home-based OSA index values likely represent the participants’ actual OSA severity because they were not restricted by cumbersome PSG devices and could freely alter their sleeping position.
This study has some limitations. First, the RootiRx data set lacked sleep staging measurements obtained through electroencephalography. The RootiRx device determines the sleep stage of the wearer by using a validated algorithm, such as a fast Fourier transform and neural networks.(26–28) Although the accuracy of the predicted sleep stage and estimated total sleep time was approximately 85–90%, the arousal response or the precise percentages of rapid eye movement (REM) sleep and non-REM sleep could not be obtained. The associations between the first-night effect, REM latency, and duration should be further explored.(29) Second, during RootiRx recording, the effects of environmental factors in the hospital and home sleep environments could not be controlled. Environmental factors include radiant temperature, air temperature, relative humidity, carbon dioxide concentration, illumination, and equivalent noise level.(30) Moreover, ECG signals are the mechanism of the RootiRx device. Thus, the CVHRI index could have been affected by abnormal heart rhythms, such as atrial fibrillation and ventricular tachycardia (with or without pacemaker implantation) and arrhythmia caused by any other type of cardiovascular condition. Hence, in patients with related heart diseases, the Rx index and CVHRI might not be accurate measures of OSA. In such patients, CEI may be a more suitable parameter for diagnosing OSA.