Obstructive sleep apnea: the state of cerebral hemodynamic reserve

Background: Individuals with obstructive  sleep apnea syndrome (OSAS) have an increased risk of disabling disorders of the cardiovascular system, including  stroke.  The  mechanisms   of OSAS effects on cerebral blood flow and cerebral vascular autoregulation have not been clear enough. Aim: To study characteristics of cerebral blood flow in patients  with OSAS and the effect of CPAP therapy on cerebral hemodynamic reserve. Materials and  methods: One  hundred and  two  patients with various OSAS severity (61 male  and  41 female) and  20 healthy  volunteers  participated in the study. We performed  ultrasound assessment of cerebral  blood  flow with functional  tests  and calculated  reactivity indices. Results: With more severe OSAS, no significant differences in cerebral vascular reactivity compared to the control group were  registered. However, there  was a trend  to some  decrease  in the  index of constriction  and dilation  in the  vertebral  arteries  and  the  basilar artery, as well as to its increase in the middle cerebral artery in severe and moderate OSAS. The index of vasomotor  reactivity of cerebral  arteries was significantly (р < 0.05) lower in patients with  severe  OSAS:  for vertebral  arteries,  up  to 38.9 ± 8.5 and for basilar artery, up to 36.8 ± 15.7, compared to  the  control  group  (52.1 ± 9.8 and 50.1 ± 11.2, respectively). In patients who initiated CPAP therapy, there were no changes  in velosity, resistance  and  reactivity parameters of cerebral vessels after 2 months. Conclusion: We were able to  confirm a significant  impairment  of cerebral vascular autoregulation  in patients  with severe OSAS, predominantly in the posterior circulatory region. CPAP-therapy of 2 months'  duration  did not lead to restoration  of cerebral hemodynamic reserve.