Sleep disordered breathing and depression : moderating impact of perceived stress and response to CPAP

Abstract

While patients with Obstructive Sleep Apnea Syndrome (OSAS) commonly have depressive symptoms, evidence about the link between OSAS and depression has been inconsistent. Similarly, while Continuous Positive Airway Pressure (CPAP) treatment for OSAS has been claimed to be effective in ameliorating depressive symptoms, results of the impact of CPAP on depressive symptoms have been inconclusive. This thesis describes two studies which aim to contribute to the clarification of these issues. The Phase 1 study examined the relationship between OSAS, depression and its subdomains and also the moderating role of current perceived stress on these relationships. Results from 254 participants using psychophysiological data on OSAS severity (Respiratory Disturbance Index, RDI; Oxygen Desaturation Index, ODI; Apnea-Hypopnea Index, AHI) did not reveal significant relationships between OSAS, depression and its subdomains. Findings were mixed in the relationship between self-report measures of OSAS severity and degree of impairment (Epworth Sleepiness Scale, ESS; Berlin Questionnaire, BQ; Self-Efficacy Measure for Sleep Apnea, SEMSA) and depression and its subdomains. While both BQ and SEMSA correlated with depression and the somatic subdomain of depression, they did not correlate with the affective subdomain. There was a small relationship between BQ and the cognitive subdomain of depression. Results from ESS did not show any significant relationships between OSAS and depression. Hierarchical Regression examining the moderating role of perceived stress in the relationship between OSAS and depression suggested that perceived stress did not moderate the relationships between these variables. The Phase 2 study involved three follow-up assessments of participants from Phase 1 comparing CPAP users and non- CPAP users. Participants were followed up at 3, 6 and 12 months after the completion of the Phase 1 study. The study investigated whether a long term treatment using CPAP improved sleepiness (ESS), depression and its subdomain and perceived stress, and also examined the moderating role of perceived stress on the relationship between any improvements in depression and sleepiness in OSAS patients. 219 participants participated in Follow-up 1, 214 in Follow-up 2 and 210 in Follow-up 3. Using repeated measures ANOVA results indicated a significant reduction in both sleepiness and depressive symptoms over the follow-up periods for both groups but no differences in these effects for the CPAP and non-CPAP participants. Similarly, the results indicated that significant improvements in perceived stress but unrelated to the use of CPAP over the 12-month period. Perceived stress did not moderate the relationship between CPAP usage and depression during all the assessments. This thesis identified the differences on the relationship between self-report measures of OSAS, psychophysiological indices of OSAS, depression and its subdomains and the probable reasons leading to these discrepancies. It also highlighted the likely causes for the reduction of sleepiness, perceived stress and depressive symptoms over time irrespective of using CPAP or not. This thesis was unique in integrating a moderating role for perceived stress on these relationships and paves the way for further investigation on moderator effects on the relationship between OSAS and depression. The limitation and suggestion for future study were also discussed. Show more