Sleep Apnea Physiological Burdens and Cardiovascular Morbidity and Mortality

Abstract

Rationale: Obstructive sleep apnea is characterized by frequent reductions in ventilation, leading to oxygen desaturations and/or arousals. Objectives: In this study, association of hypoxic burden with incident cardiovascular disease (CVD) was examined and compared with that of "ventilatory burden" and "arousal burden." Finally, we assessed the extent to which the ventilatory burden, visceral obesity, and lung function explain variations in hypoxic burden. Methods: Hypoxic, ventilatory, and arousal burdens were measured from baseline polysomnograms in the Multi-Ethnic Study of Atherosclerosis (MESA) and the Osteoporotic Fractures in Men (MrOS) studies. Ventilatory burden was defined as event-specific area under ventilation signal (mean normalized, area under the mean), and arousal burden was defined as the normalized cumulative duration of all arousals. The adjusted hazard ratios for incident CVD and mortality were calculated. Exploratory analyses quantified contributions to hypoxic burden of ventilatory burden, baseline oxygen saturation as measured by pulse oximetry, visceral obesity, and spirometry parameters. Measurements and Main Results: Hypoxic and ventilatory burdens were significantly associated with incident CVD (adjusted hazard ratio [95% confidence interval] per 1 SD increase in hypoxic burden: MESA, 1.45 [1.14, 1.84]; MrOS, 1.13 [1.02, 1.26]; ventilatory burden: MESA, 1.38 [1.11, 1.72]; MrOS, 1.12 [1.01, 1.25]), whereas arousal burden was not. Similar associations with mortality were also observed. Finally, 78% of variation in hypoxic burden was explained by ventilatory burden, whereas other factors explained only <2% of variation. Conclusions: Hypoxic and ventilatory burden predicted CVD morbidity and mortality in two population-based studies. Hypoxic burden is minimally affected by measures of adiposity and captures the risk attributable to ventilatory burden of obstructive sleep apnea rather than a tendency to desaturate.

Keywords: arousals; cardiovascular disease; hypoxic burden; obstructive sleep apnea; ventilatory burden.

Figure 1.

Example of hypoxic burden, ventilatory burden, and arousal burden calculation. Left: The overlaid $\dot{\mathrm{V}}$e and oxygen saturation as measured by pulse oximetry (Sp_O2) signals associated with all respiratory events for one individual. These signals were synchronized at the termination of respiratory events (time 0) and averaged to calculate the average event depth and duration and the search window to calculate the hypoxic burden. Right: A 3-minute period, including EEG with scored arousals, airflow with scored respiratory events, and ventilation and Sp_O2 signals.

Figure 2.

Study sample flowchart. CVD = cardiovascular disease; MESA = Multi-Ethnic Study of Atherosclerosis; MrOS = Osteoporotic Fractures in Men Study; NSRR = National Sleep Research Resource; PSG = polysomnogram.

Figure 3.

Hypoxic burden (y-axis) is strongly associated with ventilatory burden (x-axis). The R² value for this association was 0.79. HB = hypoxic burden; VB = ventilatory burden.