Duration of respiratory arrest predicts mortality risk in obstructive sleep apnea syndrome (OSAS), but not as one might imagine, concludes this study from Oregon Health & Science University. Research published in the American Journal of Respiratory and Critical Care Medicine reports that participants with short apneas and hypopneas (stopped breathing and “shallow” breathing, respectively) are at increased risk of death at 10 years.
Previous studies have shown that the apnea-hypopnea index, a widely used measure of apnea severity, is linked to mortality and heart disease. However, according to these researchers, this measure remains crude and is not a good predictor of risk for women. The study indeed shows that the duration of abnormal respiratory events could be a much more reliable predictor of mortality risk in men and women. In addition, the measurement is simple to determine, using the same polysomnography studies as those currently carried out.
The researchers analyzed the records of 5,712 adults, average age 63, participating in the National Heart, Lung, and Blood Institute (NHLBI)'s Sleep Heart Health Study and followed for 11 years. The analysis shows that:
- participants with closer breathing have a 31% increased risk of death;
- this association is strongest in participants with moderate sleep apnea: in this group, the risk of death is increased by 59%.
The result is obviously counter-intuitive., because "one would expect that long interruptions of breathing would induce a more severe prognosis, but it is quite the opposite", comments the main author, Dr Butler, professor at the Institute of Sciences of Oregon Occupational Health: "Shorter periods of breathing disturbance indicate a low threshold of arousal, associated with sleep fragmentation, elevated sympathetic tone, and increased risk of hypertension." Moreover, these results suggest that there may be several mechanisms by which sleep apnea leads to increased mortality.
The study does not demonstrate the causal link between shorter breaths and death. These shorter interruptions could be a marker of underlying issues leading to increased death tolls, rather than the cause itself.
However, the duration of respiratory disturbances does appear to be a significant predictor of mortality risk.