BACKGROUND: In patients with obstructive sleep apnea syndrome(OSAS),there are several factors increasing upper airway resistance and there is a predisposition to compromised respiratory function during waking and sleep related to constitutional factors including a tendency to obesity. Several recent studies have suggested a possible relationship between sleep apnea(SA) and systemic hypertension. But the possible pathophysiologic link between SA and hypertension is still unclear. In this study, we have examined the relationship among age, body mass index(BMI), pulmonary function parameters and polysomnographic data in patients with OSAS. And also we tried to know the difference among these parameters between hypertensive OSAS and normotensive OSAS patients. METHODS: Patients underwent a full night of polysomnography and measured pulmonary function during waking. OSAS was diagnosed if patients had more than 5 apneas per hour(apnea index, AI). A careful history of previously known or present hypertension was obtained from each patient, and patients with systolic blood pressure > or = 160mmHg and/or diastolic blood pressure > or = 95mmHg were classified as hypertensives. RESULTS: The nocturnal nadir of arterial oxygen saturation(SaO2 nadir) was negatively related to AI and respiratory disturbance index(RDI), and the degree of nocturnal oxygen desaturation(DOD) was positively related to AI and RDI. BMI contributed to AI, RDI, SaO2 nadir and DOD values. And also BMI contributed to FEV1, FEV1/FVC and DLco values. There was a correlation between airway resistance(Raw) and AI, and there was a inverse correlation between DLco and DOD. But there was no difference among these parameters between hypertensive OSAS and normotensive OSAS patients. CONCLUSION: The obesity contributed to the compromised respiratory function and the severity of OSAS. AI and RDI were important factors in the severity of hypoxia during sleep. The measurement of pulmonary function parameters including Raw and DLco may be helpful in the prediction and assessment of OSAS patients. But we could not find clear difference between hypertensive and normotensive OSAS patients.