Sleep is a physiological process with an internal program of a number of well defined sleep stages and intermediate wakefulness periods. The sleep stages do modulate the autonomous nervous system and thereby the sleep stages are accompanied by different regulation regimes for the cardiovascular and respiratory system. The differences in regulation can be distinguished by new analysis techniques on the recorded signals. In addition to normal sleep regulation some sleep disorders affect the cardiovascular and respiratory regulation. The most prevalent disorder linked to sleep and changes in the autonomous system is obstructive sleep apnea. In patients with obstructive sleep apnea marked short term changes in cardiovascular and respiratory regulation are observed during sleep. These abnormalities in regulation are further differentiated between the sleep stages. For long term changes obstructive sleep apnea is recognized as a major risk factor for arterial hypertension. Treatment of obstructive sleep apnea lowers blood pressure during the night and over time also lowers blood pressure during daytime. In this study we investigated 18 patients with sleep apnea and normal blood pressure, 10 patients with sleep apnea and arterial hypertension and 10 normal subjects as controls. Both patient groups were tested with cardiorespiratory polysomnography before and under CPAP therapy. The effects on cardiovascular and respiratory regulation during sleep and daytime are investigated in the three groups.