Composition of nocturnal hypoxaemic burden and its prognostic value for cardiovascular mortality in older community-dwelling men

Abstract

Aims: To investigate the composition of nocturnal hypoxaemic burden and its prognostic value for cardiovascular (CV) mortality in community-dwelling older men.

Methods and results: We analysed overnight oximetry data from polysomnograms obtained in 2840 men from the Outcomes of Sleep Disorders in Older Men (MrOS Sleep) study (ClinicalTrials.gov Identifier: NCT00070681) to determine the number of acute episodic desaturations per hour (oxygen desaturation index, ODI) and time spent below 90% oxygen saturation (T90) attributed to acute desaturations (T90desaturation) and to non-specific drifts in oxygen saturation (T90non-specific), respectively, and their relationship with CV mortality. After 8.8 ± 2.7 years follow-up, 185 men (6.5%) died from CV disease. T90 [hazard ratio (HR) 1.21, P < 0.001], but not ODI (HR 1.13, P = 0.06), was significantly associated with CV death in univariate analysis. T90 remained significant when adjusting for potential confounders (HR 1.16, P = 0.004). Men with T90 > 12 min were at an elevated risk of CV mortality (HR 1.59; P = 0.006). Approximately 20.7 (5.7-48.5) percent of the variation in T90 could be attributed to non-specific drifts in oxygen saturation. T90desaturation and T90non-specific were individually associated with CV death but combining both variables did not improve the prediction.

Conclusion: In community-dwelling older men, T90 is an independent predictor of CV mortality. T90 is not only a consequence of frank desaturations, but also reflects non-specific drifts in oxygen saturation, both contributing towards the association with CV death. Whether T90 can be used as a risk marker in the clinical setting and whether its reduction may constitute a treatment target warrants further study.

Keywords: Cardiovascular; Death; Hypoxaemia; Mortality; Oximetry; Sleep.

Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2018. For permissions, please email: journals.permissions@oup.com.

Figures

Figure 1

Examples of pulse oximetry traces (SaO2) derived from overnight polysomnography. (A) Low baseline oxygen saturation, but not acute desaturation events determine T90. (B) Distinct desaturations, but not baseline saturation—indicated by the blue arrows—determine T90.

Figure 2

(A) Histogram of total sleep time spent below 90% oxygen saturation (T90), T90 attributed to desaturations (T90desaturation), and to non-specific drifts of oxygen saturation (T90non-specific) across the study cohort. The inset displays a zoomed-in view for T90 ≥ 100 min. (B) Relationship between T90 indices and oxygen desaturation index (ODI). (C) Box plots of T90 quartiles in men with no, mild and moderate-to-severe sleep-disordered breathing as determined by the apnoea hypopnoea index (AHI).

Figure 3

Survival analysis of nocturnal hypoxaemic burden metrics. (A) oxygen desaturation index (ODI), (B) time spend below 90% oxygen saturation (T90); (C) T90 attributed to non-specific drifts of oxygen saturation (T90non-specific); (D) T90 attributed to acute desaturations (T90desaturation). Graphs show Kaplan–Meier curves for quartiles (Q) and log-rank test results.

Figure 4

Kaplan–Meier survival analysis of participants based on combined scores of time spend below 90% oxygen saturation (T90) attributed to non-specific drifts of oxygen saturation (T90non-specific) and T90 attributed to well-defined acute desaturations (T90desaturation). The arrows indicate high (Quartile 4) vs. low (Quartile 1–3) as defined by dichotomization (see Methods section for details).

Take home figure

In community-dwelling older men, T90 is an independent predictor of CV mortality.