Impairment of daytime cerebrovascular reactivity in patients with obstructive sleep apnoea syndrome

Several studies have demonstrated a clear association between snoring, slee p apnoea and increased risk of stroke. However, the possible role of sleep apnoea in the pathophysiogenetic mechanisms of cerebrovascular disease is s till unknown. Our aim in this study was to investigate cerebral haemodynami c changes during the waking state in eight patients with sleep apnoea syndr ome (OSAS) by means of transcranial Doppler (TCD). In particular, we studie d cerebral vascular reactivity (CVR) to hypercapnia calculated by means of the breath holding index (BHI). The investigation was performed in the earl y morning, soon after awakening, and in the late afternoon. Data were compa red with those of eight healthy subjects matched for age and vascular risk factors. OSAS patients showed significantly lower BHI values with respect t o controls both in the morning (0.56 vs. 1.36; P < 0.0001) and in the after noon (1.12 vs. 1.53; P < 0.0001). In patients, BHI values in the afternoon were significantly higher than in the morning (P < 0.0001). These data demo nstrate a diminished vasodilator reserve in OSAS patients, particularly evi dent in the morning. This reduction of the possibility of cerebral vessels to adapt functionally in response to stimulation could be linked to hyposen sitivity of cerebrovascular chemoreceptors after the continuous stress caus ed by nocturnal hypercapnia.