Sleep is understood to be an essential function in humans; and though too little sleep has a number of health and societal consequences, many people do not get enough sleep each night. There are a number of pathological conditions that contribute to poor sleep and the most common of these sleep disorders is sleep-disordered breathing (SDB), affecting 2–4% of adults in the general population. SDB is characterized by brief periods of airway occlusion during sleep, resulting in oxyhemoglobin desaturations (intermittent hypoxemia) and central nervous system arousals (sleep fragmentation) which precipitate acute cardiovascular changes and have been linked to cardiovascular disease and death. Parsing the relative contribution of hypoxemia and sleep fragmentation to the adverse health outcomes associated with SDB is an important step to developing SDB treatment strategies and identifying populations at high risk for adverse health outcomes. This project utilized novel measures for sleep fragmentation that enable the quantification of sleep structure based on the number, frequency, and hazard of sleep stage transitions. These measures were related to subjective sleep quality, SDB severity, and all-cause mortality. Overall a high frequency of sleep stage transitions were associated with increased odds of reporting poor quality sleep (chapter 2). In analysis of number of and hazard of transitioning (chapter 3), more severe SDB was related to higher numbers of transitions to and from wakefulness as well as a tendency towards faster transitions out of sleep (i.e. towards wakefulness). Finally, transitions to and from sleep increased the odds of death, while transitions within sleep decreased the likelihood of dying (chapter 4).

Measures of sleep stage transitioning have not been commonly used in analysis of sleep data. As the results presented here indicate, transitions may provide useful information for understanding the impact of sleep on human health. As consensus on the importance of good quality sleep to maintaining health and longevity continues to build more non-traditional measures of sleep should be investigated to better understand these relationships.