Participants
This study was approved by the Northwestern University Institutional Review Board and all participants completed written informed consent. Women who were undergoing polysomnography due to suspected OSA were recruited for the study from the Northwestern Medical Center Sleep Disorders Laboratory. Patients were recruited at the diagnostic, split night or titration study and completed questionnaires before CPAP was set up at home. Inclusion criteria included: female gender and CPAP naïve. Exclusionary criteria included: diagnosis of chronic obstructive pulmonary disease, neurological disorders, use of supplemental oxygen, plan to undergo surgery in the next 3 months, use of other treatments for OSA (including bariatric surgery, upper airway surgery, or oral appliance), dementia, inability to read or write in English and unstable psychiatric disorders.
Procedure
Female participants undergoing diagnostic, split night, or CPAP titration studies aged 18–70 were recruited using flyers and phone calls. Participants who were interested in the study were invited to complete questionnaires in a one hour visit to the sleep research laboratory. Pre-treatment questionnaires were scheduled after an OSA diagnosis was confirmed via polysomnography but before CPAP was set up in their home. All PSG were conducted in the laboratory (no home PSG studies) and were scored using standard AASM criteria. Patients participated in the standard clinic protocol for titration and CPAP initiation. All participants had mask fittings and CPAP education with a sleep technician at the titration or split night study. Patients were assigned to durable medical equipment (DME) companies for CPAP set-up per the clinic’s usual practices. The DME company representative again reviewed the use and care of the equipment as well as the importance of compliance. CPAP machine settings were determined by the ordering physician who was blinded to study enrollment status of each patient. Adherence was determined objectively, based on reports generated by querying the internal recording system that accompanies the CPAP devices. The data was obtained by electronic download at 10–12 weeks after treatment initiation.
Measures
Demographics: Age, gender, race, education, and income were assessed by self-report.
Depressive Symptoms: Depressive symptoms were assessed using the Center for Epidemiologic Studies Depression Scale, (CES-D; Radloff
1977). This 20-item measure is a commonly used and well-validated measure of depressive symptoms in which scores ≥ 16 are associated with clinically elevated depressive symptoms in middle-aged and older adults.
Subjective Sleepiness: The Epworth Sleepiness Scale (ESS) was used to assess self-reported subjective sleepiness at baseline (Johns
1991). In this questionnaire, participants rate the likelihood they would fall asleep in 8 different situations, such as being a passenger in a car. Scores range from 0–24 and scores >10 have been associated with excessive sleepiness (Johns
1991).
Relationship Quality: Relationship quality was measured by the Quality of Relationship Inventory (QRI) support and conflict subscales at baseline and follow-up (Pierce et al.
1991). The support subscale contained items related to emotional support in the marriage, such as “To what extent could you count on your spouse for help with a problem?” and “To what extent could you count on this person to listen to you when you are very angry at someone else?” The conflict subscale contained items related to the frequency and extent of marital conflict, such as, “How angry does your spouse make you feel?” and “How often do you have to work hard to avoid conflict with your spouse?” Subscales were scored as the average of the 7 support items and average of the 12 conflict items. Reported test-retest reliability correlations ranged from 0.48 to 0.79 (Pierce et al.
1997; Verhofstadt et al.
2006). This questionnaire in our sample demonstrated adequate internal consistency (Cronbach’s alpha = 0.80 for the support subscale and 0.74 for the conflict subscale).
Social Support: Social support was measured using the Enhancing Recovery in Coronary Heart Disease Patients social support index (ESSI) (Mitchell et al.
2003). This 8 item questionnaire measures structural, instrumental, and emotional social support. Scores range from 8 to 34, with higher scores indicating greater social support. This measure had good internal consistency in our sample (Cronbach’s alpha = 0.86). Although it was developed in cardiac patients, this measure has been used in other medical populations including cancer and HIV (Penedo et al.
2012; Mergenova et al.
2016).
Sleep Apnea Self-Efficacy: Self efficacy related to sleep apnea was measured by the Self Efficacy Measure for Sleep Apnea. This 26-item measure contains 3 subscales: risk perception of OSA (e.g., “chances of falling asleep driving”), outcome expectancies of CPAP (e.g., “job performance will improve”), and treatment self-efficacy (e.g., “I would use CPAP if it made my nose stuffy”). Patients completed this measure at baseline. In validation studies of OSA patients, this scale demonstrated good psychometric properties. Cronbach’s alpha was reported as 0.90 for the total scale, 0.85–0.89 for the 3 subscales and reported test-retest reliabilities ranged from 0.68–0.77 (Weaver et al.
2003). In our sample, Cronbach’s alpha was between 0.70 and 0.89.
Perceived important of OSA treatment: We assessed perceived importance for OSA treatment in one item: “How important is it to you that you are treated for OSA”. Item responses range from 0 (not at all) to 5 (very motivated).
Pre-sleep Arousal was measured by the Pre-sleep arousal scale (Nicassio et al.
1985). This 16 item scale has two subscales “cognitive” and “somatic”. Items for the cognitive arousal subscale include the feeling of having an active mind before sleep, anxious or depressed thoughts. The somatic pre-sleep arousal subscale includes physical feelings of anxiety and restlessness before sleep, such as a racing heart. Items are scored from 1 (not at all) to 4 (extremely). Scores range from 8–40. This scale has demonstrated adequate reliability and internal validity (Nicassio et al.
1985; Jansson-Frojmark and Norell-Clarke
2012).
Insomnia Symptoms were measured by the Insomnia Severity Index (ISI). This 5 item scale assesses symptoms of insomnia as well as satisfaction with quality of sleep and concern about the impact of sleep on quality of life (Morin
1993). Chronbach’s alpha demonstrated adequate internal consistency (0.74) and this measure has been demonstrated to have adequate concurrent validity and sensitivity to improvements in sleep (Bastien et al.
2001).
Apnea severity was determined by the apnea severity index (apnea or hypopnea events per hour) on the diagnostic polysomnography or the diagnostic portion of the split night polysomnogram.
Data analysis
Data were analyzed using SPSS Version 20. Participant characteristics were described using means, standard deviations, and percentages. Associations between relationship status, quality, and CPAP adherence were evaluated using Pearson correlations and linear regression. All tests were 2-tailed and statistical significance was defined as p < 0.05.