Determinants of the awakening rise in systemic blood pressure in obstructive sleep apnea syndrome

To investigate the factors responsible for the morning rise in blood pressure (BP) in obstructive sleep apnea syndrome (OSAS) we examined a group of 253 consecutive snorers or OSAS patients. On the basis of their AHI the patients were classified in four groups. BP was measured on the evening before sleep onset and on the following morning after 15 min of rest by a finger arterial pressure device (Finapres). In 150 subjects BP was monitored during the night by a Finapres device. In the morning BP increased in the patient group with an average difference of 9.9 +/- 0.5 mmHg for systolic (SBP) and 9.9 +/- 0.4 mmHg for diastolic pressure (DBP). The increase was significant in snorers and OSAS patients without differences between groups. The morning rise in SBP was related to diurnal values of SBP, age and AHI whereas the time spent in apnea and the diurnal values of DBP significantly contributed to the DBP increase. In the subgroup of 150 patients in whom BP was analyzed during sleep, the awakening increase was related to the absolute BP value during sleep and to the BP changes from wakefulness to sleep. The magnitude of the BP changes from evening to morning was not dependent on the degree of BP variability during sleep. We conclude that the awakening increase in BP in patients with snoring or OSAS may be mediated by the setting of pressure response to apnea or to mechanical effort during sleep. Anthropometric variables and diurnal cardiovascular setting may play an additional role in modulating the final pressure response to upper airway obstruction.