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.

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.