Sleep position and its effects on OSA severity have been researched for years with conflicting data and results. In 1930 Johnson and colleagues published a paper entitled “In what positions do healthy people sleep?” . The authors took pictures of a person asleep with a “telechron clock, which hangs beside the bed” and reported “a repertoire of more than a dozen gross postures” of sleep. A 1983 study describes 20 to 40 different sleep positions in a single night . Currently four sleep positions are described that refer to trunk orientation. This decreases the number of body shifts, which is around 11 per night . In the majority of patients, the severity of OSA increases while sleeping supine, and in up to 60%, AHI is 50% or greater in supine than non-supine sleep . That makes it clinically important, to identify supine and non-supine sleep positions to interpret the sleep study correctly and to make sure that the proportion of supine sleep during a single night sleep study reflects natural home sleep.
In this pilot study, we describe four patterns of supine/non-supine sleep that may become important in the phenotyping process in personalizing sleep medicine. This could help in classifying patients into different prognostic and therapeutic categories . Interestingly, a study by Mokros et al. showed that normal BMI has a very high negative predictive value for moderate to severe OSA in the lateral position, virtually excluding it in this position . Therefore, in non-obese patients, increased supine sleep (affected by PSG equipment during a sleep study) may significantly overestimate the severity of OSA. This would be similar in the Asian population, where the prevalence of pOSA has been shown to be higher [20, 21]. Also, after upper airway surgery for OSA patients become more positional dependent. Therefore an increased supine sleep during a post-op PSG is likely to significantly affect the study results [22, 23].
In our study, group 1 and 2 have a stable proportion of supine sleep regardless of measurements in-lab or at home. In these groups, the result of PSG is reliable, at least in terms of pOSA. Group 3 shows a night-to-night variability, and group 4 shows a significant difference between PSG and home sleep. In groups 3 and 4, a single-night study is not reliable and may significantly overdiagnose OSA severity. As the amount of supine sleep is one of the important factors of night-to-night variability leading to OSA severity, group 3 patients with positional OSA would also be the individuals with the highest AHI variability during consecutive PSGs and nights . Interestingly, in group 4, 6 of 7 patients had an AHI ≥ 15, and among them, 3 (50%) had positional OSA. In these three patients, the result of one night PSG could significantly overestimate the severity of OSA. This pilot study makes a strong argument against single-night sleep studies. pOSA patients from group 4 might also be mistakenly prescribed positional therapy (PT) based on one-night sleep study . This type of treatment requires not only the patient to be positional-dependent, but also to sleep long enough in supine position during regular home sleep. If an individual sleeps a high proportion of the PSG night in the supine position and does not sleep supine at home, PT might be the wrong and ineffective treatment.
Another important result of this study is the difference in mean amount of supine sleep during PSG and home sleep. In a previous study, we reported retrospectively a mean supine sleep of 44% on 445 consecutive patients undergoing PSG . The current study reports that mean supine sleep during PSG is 55% (median 61%) and during home sleep using Clebre HSAT is 35% (median 26%). Sorscher et al. studied how well patients can estimate supine versus non-supine sleep . The mean estimated supine sleep was 20% as reported by the patient, compared to 41% during a HSAT. They concluded that patients underestimate supine sleep by up to 50%. Gordon et al. used videotaping alone on 2 nights and also reported 22% of supine sleep . It is possible that patients do not underestimate supine sleep at home, as suggested by Sorscher et al., but that they simply sleep more supine during PSG due to the unfamiliar environment and use of multiple monitors.
Vonk et al. reported supine sleep in participants with positional OSA, of 43% and 29% during PSG and HSAT, respectively, using the sleep positional trainer (SPT) . Wimaleswaren et al. (conference abstract) reported on 19 patients with supine sleep of 35% and 25% during PSG and HSAT, respectively, using a body position sensor (night shift) . However, the accuracy of the night shift sensor has been questioned in another study reporting that in 2 out of 20 patients, night shift under-reported supine sleep, one in a situation of trunk supine and neck upright position and the other with trunk supine and head lateral position . The Clebre sensor used in this study is mounted on the suprasternal notch and may be a more accurate way of measuring supine sleep at home. In a previous study, we showed a 97% accuracy of Clebre sensor in detecting supine vs non-supine sleep position compared to NOX A1 PSG .
There are several limitations in this study that need to be recognized and addressed in the future research. First, the sample size in this pilot study is small which may account for the lack of correlation between sleep position and AHI, BMI, ESS, sex, or age. Another major limitation is the use of new technology that requires more study but shows great promise especially for community-based research. Additionally, using PSG and Clebre in the lab may have allowed the patients to get used to sleeping with monitors and to affect future results. The sequence of monitoring should be changed for some patients in future studies. Finally, different factors such as room temperature or humidity, as well as multiple comorbidities (cardiovascular, neuromuscular, etc.), can potentially influence the sleep positions chosen by a patient and require further study.
The strength of the study is the use of a sensor in the lab and at home which enabled detection of sleep positions that were compared to PSG  in consecutive patients. This HSAT leads to a minimal disturbance to sleep physiology and to the ability to study the same participants in the lab and for several nights at home.