Sleep disordered breathing, hypoxia and inflammation: associations with sickness behaviour in community dwelling elderly with and without cardiovascular disease.

BACKGROUND: Inflammation can induce a cluster of symptoms, referred to as sickness behaviour (e.g., depressive symptoms, sleep disturbances, pain and fatigue). Cardiovascular disease (CVD) and sleep disordered breathing (SDB) are common in older adults. CVD is associated with an increased inflammatory activity and in SDB, hypoxia can also increase inflammation. The purpose of this study is to explore if SDB-related hypoxia is associated differently with inflammation and the presence of sickness behaviour in older adults with and without CVD.

METHODS: Three hundred and thirty-one older adults, whose mean age is 78 years, underwent one-night polygraphic recording to measure SDB and hypoxia. CVD was established by a clinical investigation. Questionnaires were used to measure sickness behaviour and depressive symptoms. High sensitivity C-reactive protein was used as a marker of inflammation.

RESULTS: Structural Equation Modelling showed that SDB-related hypoxia was associated with inflammation (β > 0.40) which mediated indirect associations with sickness behaviour (β = 0.19) and depressive symptoms (β = 0.11), but only in those with CVD (n = 119). In this model, inflammation had a direct effect on sickness behaviour (β = 0.43) and an indirect effect on depressive symptoms (β = 0.24). Hypoxia had the strongest effect (i.e., β = 0.41; significant) on inflammation, whereas the AHI or ODI had weak and non-significant effects (β = 0.03 and β = 0.15).

CONCLUSIONS: Older adults with CVD and SDB are at a particular risk of developing sickness behaviour and depressive symptoms. The effect of SDB was mainly caused by hypoxia, suggesting that hypoxia is an important marker of SDB severity in older adults with CVD.