Study design and participants
In this preliminary single-arm, non-randomized study, all participants completed overnight polysomnography with recording of head angles during sleep at the Mass Lung & Allergy, P.C. Sleep Disorders Center (Worcester, MA) between November 2016 and November 2017. The study was conducted in accordance with the Declaration of Helsinki and International Conference on Harmonisation (ICH) guidelines for Good Clinical Practice, and the study protocol was reviewed and approved by the New England IRB (Newton, MA). Participants were informed of the purpose of the study and provided written informed consent. Eligible participants were 21–60 years of age with a diagnosis of positional OSA from recent polysomnography results using the AASM guidelines of positional OSA defined as a lower AHI in the non-supine position than in supine (de Vries et al. 2015). Participants self-reported daytime drowsiness that persisted with use of continuous positive airway pressure (CPAP) therapy. They had to show compliance with CPAP use in the week prior to the screening visit, follow directions during an overnight sleep study, and discontinue CPAP therapy for two consecutive nights. Exclusion criteria included documented diagnosis of insomnia, chronic ear infections, persistent neck pain, persistent chronic posture physical issues, previous C-spine fusion, history of cardiac arrythmia, history of seizures, allergy to standard tape used in sleep centers, non-English speaking, hospitalization within the previous 4 weeks, use of antibiotics or steroids within the previous 4 weeks, any major uncontrolled disease or condition, such as congestive heart failure, malignancy, end-stage heart disease, amyotrophic lateral sclerosis (ALS), or severe stroke, or other condition as deemed appropriate by investigator, history of severe osteoporosis, excessive alcohol intake (> 6 oz hard liquor, 48 oz beer or 20 oz wine daily), or illicit drug use, and daily use of prescribed narcotics (> 30 mg morphine equivalent).
Sleep study and head rotation measurement
A proprietary sensor patch (Sleep Systems, LLC, Bedford, NH, USA) was developed for this trial and integrated with a dual axis inclinometer (SignalQuest, Lebanon, NH, USA), which was then packaged by Sleep Systems, LLC into a bedside unit fitted to the Embla communication system for the polysomnography montage. Before sleep, the sensor patch was attached to the participant’s forehead with adhesive and tape. The sensor was calibrated for each participant for head rotation angles 0° to 180° and head incline angles of 0° to 90°. Head rotation of 90° corresponds to lying supine with the head facing the ceiling; head rotation of 0° and 180° correspond to the head rotated fully to the right or left horizon, respectively (Fig. 1A). Using Fowler’s positioning model, head incline of 0° corresponds to lying supine with head facing the ceiling and 90° represents sitting upright (Fig. 1B).
Each participant was asked to fall asleep in their usual torso and head position for sleeping. Once asleep, data were recorded for all head and torso positions at as many of these positions as allowed. Each participant was coached in all sleeping positions for at least 30 min to collect data. Standard polysomnogram data were collected during the overnight study by a sleep research technologist, including 6-channel electroencephalogram (EEG), left and right electrooculogram (EOG), three chin electromyography (EMG), snoring sensor, airflow measured by oronasal thermistor and nasal pressure transducer, respiratory effort measured by thoracic and abdominal respiratory inductance plethysmography, pulse oximetry, left and right anterior tibialis EMG, electrocardiogram, body position and integrated digital audio and video recordings.
Sleep research technologists, who were blinded to head position associated with each sleep epoch, performed sleep and event scoring in accordance with The American Academy of Sleep Medicine Manual for the Scoring of Sleep and Events Version 2.0.3 (The and Manual for the Scoring of Sleep and Associated Events: Rules, Terminology, and Technical Specifications.Darien, IL:American Academy of Sleep Medicine 2014). In addition to standard polysomnogram data collection, AHI (total number of apnea and hypopnea episodes per hour of sleep), SpO2, torso position, and head rotation angle and head incline angle as determined by the forehead sensor, were recorded for each sleep epoch (defined as a period of sleep that maintained head angle with angular consistency ≤ 2°). The peak AHI was calculated for every epoch as the highest AHI of each head rotational subgroup.
The polysomnogram montages were specifically altered to include investigational channels for head rotation and head incline angles. A custom interface was developed to maintain compatibility with specific bedside polysomnography recorder auxiliary inputs. Small sponge wedges were added to compensate for individual forehead shape to keep angular errors ≤ 2°.
Body and head positioning during sleep
During the overnight sleep test, participants were coached by sleep research technologists to sleep with head rotation angles of ≤ 20°, 30–150°, and ≥ 160°, where horizon refers to head rotation fully to the left (180°) or right (0°). Each rotation angle was measured and recorded by the participant’s forehead sensor. Each head position was attempted with the torso in both supine and non-supine positions. The sleep research technologist-initiated changes in head position from right to left at specific degrees after a minimum sleep epoch duration of 10 min (goal 30 min) by placement of pillow wedges to keep the head stable at each angle. However, participants were able to change position while they slept. All positions, both coached and natural, were recorded for each sleep epoch.
Primary and secondary outcomes
The primary outcome was change in AHI severity with head rotation ≤ 20° above the horizon compared with > 20° above the horizon. The secondary outcome was change in SpO2 associated with head rotation ≤ 20° above the horizon vs > 20° above the horizon. To determine the effect of torso position on AHI, the peak AHI was calculated for sleep epochs when the participant was sleeping with torso supine compared with sleep epochs with torso non-supine (i.e., sleeping on right or left side or prone).
Formal power calculations were not performed for this exploratory analysis. All analyses were two-sided with a significance level at P < 0.05 and reported with 95% confidence levels. Data were analyzed for AHI and SpO2 dependence on head rotation ≤ 20° and > 20° above the horizon. Mean AHI was also calculated for supine versus non-supine torso positions overall and within the head rotation angle subgroups of ≤ 20° and > 20° above the horizon.