Aims: Near-infrared spectroscopy (NIRS) is a non-invasive, easy to apply, optical technology for measuring cerebral blood oxygenation, but there is lack of comprehensive population data to aid interpretation and clinical use. Given the importance of cerebral perfusion in the context of evolving guideline recommendations for more aggressive lowering of blood pressure (BP) in hypertension, even in the oldest old, understanding of normative NIRS values is timely. We estimated normative values of cerebral oxygenation measured by NIRS in a large community-dwelling population sample of adults aged > = 50 years (n = 3110). We hypothesized that measurements would be attenuated by cardiovascular risk factors.
Methods: Data from Wave 3 of The Irish Longitudinal Study on Ageing (TILDA) was utilized. Frontal lobe cerebral oxygenation was continuously measured via a Portalite, while participants rested in the supine position. Beat-to-beat BP was measured simultaneously. Normative data was modelled using generalized additive models for location, scale, and shape (GAMLSS). Multivariate linear regressions were used to examine associations with cardiovascular risk factors.
Results: All three measures of NIRS (TSI, O2Hb and HHb) declined with increasing age. O2Hb and HHb were significantly lower in males than females. Increased smoking, excess alcohol intake, a higher waist-hip ratio, diabetes, angina, congestive heart failure, transient ischemic attack and total cardiovascular disease burden were all associated with decreased cerebral oxygenation.
Conclusion: We present for the first time, normative resting-state NIRS reference data from a large population, which contributes to clinical interpretation of NIRS and advances the use of NIRS as a standard clinical tool.
Keywords: Aging; Cerebral oxygenation; NIRS; Near infra-red spectroscopy; Resting-state.
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