A Study Of The Physiological Effects Of Sleep Apnea On Cerebral Blood Flow Velocity

It is estimated that sleep apnea is prevalent in the US in about 18 million people. The prevalence rate is approximately 6% in the US. Sleep apnea reduces the quality of life of patients. Sleep apnea is characterized by repetitive pauses in breathing during sleep. Recent studies also show loss of gray matter in people diagnosed with sleep apnea. To study the physiological effects of sleep apnea on cerebral blood flow velocity (CBFV), CBFV was measured in subjects simulating apnea. Sixteen volunteers (29 ± 5 yr and BMI 24.1±4.8, 9M and 7F) were recruited as control subjects. We measured CBFV with the Transcranial Doppler (TCD) and two protocols varying in the length of normal breathing between breath holds were followed for simulating apnea. The volunteers performed the maneuvers in two different positions, sitting and supine. Order of the protocols was randomized. We also studied five volunteer subjects (53.6 ± 7.4 yrs and BMI 33.66±7.27, 4M and 1F) undergoing an in-lab sleep apnea test (8 hour polysomnography). We hypothesized that there is an increase in the CBFV during sleep apnea. Various metrics were extracted from this data and comparisons were made between the measurements for the periods of normal breathing versus those during periods of apnea. The results show a significant increase in the trend of the velocity during apnea as compared to the trend of velocity during normal breathing. In the simulated apnea study, we found that the mean slope of the trend of the maximum velocity was 0.45X10-3± 0.75 X10-5 cm/s2 during normal breathing in the sitting position was and 0.76 X10-4 ± 0.19X10-7 cm/s2 in the supine position but these values increased to 0.12X10-2 ± 0.24X10-4 in the sitting position and 0.015 ± 0.112X10-3cm/s2 in the supine position during simulated apnea. In the sleep apnea study, we found that the slopes of the trends increased from 0.25X10-2 ± 0.56X10-3 cm/s2 during normal breathings to 0.005 ± 0.528 X10-4cm/s2 during hypopnea and 0.0075 ± 0.365 X10-3 cm/s2 during apnea. From these results, we can conclude that the CBFV increased during simulated apnea and also during apnea and hypopnea as compared to normal breathing.