Although strong associations have been demonstrated between sleep disordered breathing and cardiovascular diseases, much is not known regarding the mechanisms by which SDB produces blood pressure changes and increases morbidity. Further analysis of the polysomnography and blood pressure data could yield important insights into the physiologic events responsible for cardiovascular morbidity. Such information could then be used to develop diagnostic tests that identify those people at highest risk and thus who might especially benefit from intervention. This would be of potentially great public health importance, given the prevalence of SDB and the availability of treatments for SDB.