The investigators used the computerized database of the Wisconsin Sleep Cohort to answer the following specific questions. What were the physiologic characteristics of SDB events in the non-clinical population in terms of severity, high airway resistance, obstructive and central components and associated after-effects on EEG arousal and ventilatory overshoots? Did these important elements of the SDB event change as SDB progressed over time? Did the ventilatory or cardiovascular consequences of apnea or hypopnea and its immediate aftermath determine the likelihood of subsequent sleep-disordered breathing events? 2. What were the immediate and long-term cardiovascular consequences of sleep-disordered breathing events; what characteristics of these SDB events (such as oxygen desaturation, arousal, ventilatory overshoot airway resistance, etc.) determined the cardiovascular responses and consequences? 3. What was the effect of aging on SDB and its sequelae as studied in the truly healthy elderly? 4. What role did anatomical characteristics of the upper airway play in determining the frequency and severity and type of sleep-disordered breathing? Did these anatomical determinants differ in the general non-clinical population versus the obstructive sleep apnea (OSA) population? ... in the obese versus the non-obese?