To examine the roles of obstructive apnea (OA) and central apnea (CA) in oxygen desaturation on hypertension and sleep apnea syndrome (SAS), we performed a sleep study on 41 elderly subjects (mean age 69.5 +/- 6.8 years, male:female = 31:10). Nocturnal oxygen desaturation was documented with a pulse oximeter and apneas (OA and CA) were diagnosed on the basis of results of respiratory inductive plethysmography and oronasal flow. Significant desaturation (SDS, greater than 5% drop in SpO2 from baseline value) and desaturation index (DI; epsilon SDS (%) x duration (hour)) were calculated using the continuous nocturnal monitoring system with a pulse oximeter. We defined central type apnea above 50% as the central type group (n = 8, mean age 58.6 +/- 2.9, mean BMI 21.3 +/- 1.0, male:female = 7:1), and obstructive type and mixed type apnea above 50% as the obstructive type group (n = 21, mean age 70.0 +/- 3.2, mean BMI 25.3 +/- 1.0, male:female = 17:4). Other subjects were assigned to the control group (n = 12, mean age 64.3 +/- 2.3, mean BMI 23.8 +/- 1.2, male:female = 7:5). The DI (delta 5%) of the central type was 0.34 +/- 0.17, and that of the obstructive type was 1.78 +/- 0.7 showing a significant increase in the latter compared to the control group (p < 0.02). The DI (< 90%) of the central type was 0.14 +/- 0.07, and that of the obstructive type was 1.72 +/- 0.75, and that of the obstructive type was significantly greater than in the control group (p < 0.05) and central type (p < 0.05). There were 4 cases (33.3%) with hypertension in the control group and 4 cases (50.0%) with hypertension in the central type group, but there were 15 cases (71.4%) with hypertension in the obstructive type group. Hypertensive prevalence in the obstructive group was significantly more than in the control group (p < 0.05). No significant difference in body mass index or age were seen in the obstructive group and control group. There was a significant correlation between mean blood pressure and apnea index (AI). The AI of the hypertensive group was significantly higher than that of the normotensive group (p < 0.001). These results suggest that subjects with significant obstructive apneas may be at greater risk for hypertension than subjects with central apneas and that hypertension in the pathogenesis of SAS may be related to the severity of apneas rather than oxyhemoglobin desaturation.