Cerebral autoregulation in patients with obstructive sleep apnea-hypopnea syndrome

Objective To evaluate the cerebral autoregulation in patients with obstructive sleep apnea-hypopnea syndrome （OASHS） using transcranial Doppler （TCD）-CO2 test and head-upright tilt test （HUTT） from the aspects of nocturnal hypoxemia/hypercapnia and sleep structure. Methods Seventy-six patients with OSAHS visiting our hospital from February 2007 to May 2009 were chosen in our study and divided into severe OSAHS group （n=26）, moderate OSAHS group （n=29） and mild OSAHS group （n=21） according to the apnea-hypopnea index （AHI）, and the lowest oxygen saturation （LSaO2）; 32 healthy controls, having snore history, were adopted too. Polysomnography monitor was used for night-7-h sleep monitoring and blood pressure monitoring; sleep-related indicators and blood pressure at different times were analyzed. Cerebrovascular reactivity was calculated in terms of the breath-holding index （BHI） and vascular motor reactivity （VMR） by TCD-CO2 test; Changes of cerebral blood flow velocity （CBFV）, blood pressure （Bp）, and the time from squatting-to-tilt position for the mean arterial pressure （TMAP） and the CBFV （TCBFV） returning to 〉90% of baseline levels were detected by HUTT to assess the cerebral pressure-autoregulation. Results The AHI, microarousal index （MI） and the percentages of S1 in the non-rapid eye movement sleep period in the severe, moderate and mild OSAHS groups were all significantly higher than those in the control group （P〈0.05）; the LSaO2 and the percentages of S3＋4 in the non-rapid eye movement sleep period in all the OSAHS groups were significantly lower than those in the control group （P〈0.05）; no significant difference in blood pressure before apnea was noted between the OSAHS groups and the control group （P〉0.05）, however, the systolic blood pressure while apnea in all the OSAHS groups was significantly higher than that in the control group （P〈0.05）. As compared with the controls and mild OSAHS group （1.89±0.36, 1.75±0.41）, severe and moderate OSAHS groups （0.71 ±0.17, 1.12±0.23, respectively） showed significantly decreased BHI （P〈0.05）; As compared with the controls （0.68±0.11）, and the mild, moderate and severe OSAHS groups （0.20±0.04, 0.34±0.07 and 0.55±0.17, respectively） showed significantly decreased VMR （P〈0.05）; TMAP in the moderate and severe OSAHS groups was significantly longer than that in the controls and mild OSAHS group （P〈0.05）; TCBFV in the mild, moderate and severe OSAHS groups was significantly longer than that in the controls （P〈0.05）. Significant difference on the levels of Bp and CBFV during tilt was noted between the moderate and severe OSAHS groups （P〈0.05）; Pearson analysis showed a linkage between Bp and CBFV changes （r=0.384, P=0.005）. Conclusion Cerebrovascular autoregulation is impaired in patients with OSAHS, especially in the moderate and severe groups, which may increase the risk of stroke. The major risk factors for cerebrovascular autoregulation in patients with OSAHS are night hypoxemia, hypercapnia, blood pressure fluctuation and severe sleep disorders. Key words: Sleep apnea, obstructive;  Cerebrovascular autoregulation;  Transcranial Doppler ultrasonography