Polysomnography and sleep position, a Heisenberg phenomenon? A large-scale series

Background The severity of position-dependent obstructive sleep apnea (POSA) depends on the nonsupine and supine apnea–hypopnea index (AHI) as well as the time spent in supine position. The latter in particular is susceptible to variation. Several small-scale studies suggest that wearing polysomnography (PSG) apparatus leads to an increase in supine sleeping position.
Objectives The aim of this study was to evaluate the effect of wearing PSG apparatus on sleeping position and on OSA severity.
Material and methods A large-scale, retrospective study was performed, including a consecutive series of POSA and non-apneic snoring patients who were prescribed positional therapy (Sleep Position Trainer [SPT]). The effect of wearing PSG apparatus on sleeping position was evaluated by comparing body position during the PSG night and inactive (diagnostic) phase of SPT.
Results The mean percentage of total recording time (TRT) in supine position was 43.1% during the PSG night phase compared with 28.6% of TRT during the inactive (diagnostic) phase of SPT; i.e., a significant decrease of 33.6% (p < 0.001). When adjusting the AHI using TRT in different sleeping positions measured with the SPT, the median AHI decreased from 13.3/h (9.0–20.4) to 10.3/h (6.8–16.2); p < 0.001. When using the adjusted AHI, 33% (N = 66) of all patients had a change in OSA severity.
Conclusions The results of this study indicate that wearing PSG apparatus leads to an increase in the percentage of supine sleeping position causing an overestimation of OSA severity, especially in patients with POSA. This can have significant impact on both clinical and scientific practice.