Hypercapnia and hypoxia increase ICP, due to a cerebral arterial vasodilation, decreasing cerebral resistance, and increasing CBF. We found a decrease in the CPP during apnea. Loeppky et al found an abnormal cerebrovascular response to carbon dioxide in awake patients with sleep apnea. It is therefore not known whether CBF decreases (due to decreasing stroke volume), increases (due to decreasing cerebral resistance), or remains unchanged during the apneic episode. If CBF is affected during the apnea, then the cerebral autoregulation is overcome.
If CBF ceases during apnea, this might even worsen the cerebral hypoxia developing during the apneic episodes. In our opinion, this is of major importance and should be determined in future studies in order to understand the cerebral consequences of sleep apnea.
Awake ICP was found to be elevated in these patients. Awake values for Po2 and Pco2 were normal. None of the patients had any known cause for the increased ICP evaluated by the CT scan, and only one patient had hypertension (>160/95 mm Hg). None of the patients showed any signs of hypertensive encephalopathy; however, repetitive ICP and CBF variations are assumed to dispose to increased ICP. This assumption is supported by the finding that ICP was higher in the morning. read only
The ICP pressure waves observed in these patients are characterized as pressure elevations following the apneic episodes, with an occurrence of one to three per minute, and this fulfills the definition of “B waves.” The ICP elevations during REM sleep can be included in the definition of ICP A waves. Symon et al noted that A waves occurred during REM sleep. The findings in this study point out th$ the ICP elevations during REM sleep are due the longer apneic episodes in this sleep stage and thereby ICP elevations giving rise to ICP A waves.
The awake and sleep apnea-related ICP elevations may be of importance in understanding the cerebral symptoms in patients with sleep apnea, especially the headaches and cognitive impairment which are prevalent in patients with sleep apnea.
In epidemiologic studies, snorers have been found to have an increased prevalence of cardiovascular complications. The ICP, CPP, and the possible changes in CBF during apnea indicate that one of the major risks for patients with sleep apnea is cerebral ischemia. This assumption is supported by the finding that snorers have a higher incidence of strokes.
Little is still known about the natural history of OSA, but the findings in this study indicate that one of the major risks in OSA is cerebrovascular complications. Moreover, in patients with B waves and A waves in the ICP during sleep, OSA should be considered.