The effect of continuous positive airway pressure on total cerebral blood flow in 23 healthy awake volunteers

Continuous positive airway pressure (CPAP) is the gold standard treatment for obstructive sleep apnea (OSAS). However, the influence of CPAP on cerebral blood flow (CBF) is not well understood. Ultrasound can be used to estimate CBF, but there is no widespread accepted protocol. This study investigates the influence of CPAP on total CBF in 23 healthy awake subjects by measuring flow velocity (FV) and lumen diameter of the left and right proximal Internal Carotid Arteries (ICA), Vertebral Arteries (VA), and Middle Cerebral Arteries (MCA) using Duplex Color Doppler Ultrasound (US) with and without CPAP at a level of 15 cm H₂O. Transcutaneous Carbon Dioxide (PtcCO2) level, heart rate, Blood Pressure (BP), and oxygen saturation (SaO₂) were monitored before and after each test. The measurements indicate that CPAP results in a decrease of CBF by 12.5% (p-value <; 0.05). The theoretically predicted decrease in CBF from PtcCO2 variation was 6.5%. This method allows a noninvasive bedside estimation of CBF. An increase in mean airway pressure of 15 cm H₂O significantly decreases CBF likely due to indirect effect on PtcCO2 level. These results support that the effect of CPAP on total CBF should be further explored in stroke patients before CPAP is widely used as an early treatment of sleep apnea.