A new technique for detecting sleep apnea-related "midnight" surge of blood pressure

Patients with obstructive sleep apnea syndrome (OSAS) have been reported to be at greater risk for cardiovascular events, and midnight surge of blood pressure (BP) may be a mechanism of sleep apnea-related cardiovascular risk. However, there has been no accurate noninvasive technique to detect intermittent BP surge at the time of each sleep apnea episode. We therefore developed an experimental system to detect apnea-related short-term BP surge based on BP measurement triggered by peripheral (finger-tip) oxygen desaturation (a desaturation-triggered BP monitoring system). In 16 patients with OSAS, this new system successfully detected BP surges at the time of the sleep apnea, and the BP values were found to be significantly higher than those detected using a conventional fixed interval BP monitoring system (systolic BP [SBP] difference: 13 +/- 5.8 mmHg, p = 0.039; diastolic BP [DBP] difference: 10 +/- 6.8 mmHg, p = 0.032). The maximum SBP time rate (velocity of BP surge) showed a strong positive correlation with the apnea-hypopnea index (r = 0.855, p < 0.0001). In conclusion, we developed a noninvasive oxygen desaturation-triggered BP monitoring system that can successfully detect sleep apnea-related BP surge. The midnight BP surge detected by this new method was significantly associated with the severity of OSAS.