Chest
Volume 110, Issue 3, September 1996, Pages 670-679
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clinical investigations
Sleep Apnea Syndrome and Cerebral Hemodynamics

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The dynamics of cerebral blood flow velocity (CBFV) during sleep were investigated in the right middle cerebral artery of 10 patients with sleep apnea syndrome (SAS) (mean age, 37 years) and 10 healthy control subjects (mean age, 32 years) throughout the entire sleep period. A computer-assisted pulsed (2 MHz) transcranial Doppler ultrasonography system was modified for continuous long-term and on-line recording of cerebral hemodynamics. Concurrently, simultaneous polysomnography, continuous BP recordings, and measurement of the end-expiratory carbon dioxide were undertaken. CBFV showed comparable nocturnal profiles in both groups with decreases during non-rapid eye movement (NREM) sleep and increases during rapid eye movement (REM) sleep, indicating that the general pattern of brain perfusion during normal sleep is maintained in SAS. Sleep stage changes were not regularly accompanied by corresponding changes in CBFV. This reflected a quantitative uncoupling between cerebral electrical activity and cerebral perfusion during sleep and indicated a dissociation in the activity of central regulatory mechanisms. Sleep stage-related analysis showed slightly reduced CBFV in patients with SAS compared with healthy control subjects during wakefulness and the first NREM sleep period, suggesting depressed brain activity in the patient group. The higher CBFV values observed in patients with SAS compared with control subjects during REM sleep and sleep stage 2, both preceding and following REM sleep, underline the influence of dynamically changing sleep patterns on cerebral perfusion in these patients. Reproducible rapid decreases in CBFV were related to EEG arousals. Since apneas are terminated by arousals, these results showed that direct neuronal influences on brain perfusion during apnea are evident.

Section snippets

Subjects

Subjects were recruited for the investigation after the study had been approved by the local ethics committee. A total of 16 patients with SAS and 16 healthy individuals participated in the study after giving their informed consent. Six patients and six healthy subjects were excluded from data analysis because of movement artifacts with subsequent probe dislocation. Recordings of the right middle cerebral artery (MCA) of 10 patients with SAS (mean age, 37 years) and 10 control subjects (mean

Results

Patients and control subjects showed a gradual reduction in MFV, as compared with wake values, during deepening NREM sleep in the first sleep cycle. Even intermittent increases in depth of sleep did not affect the continuously decreasing mean level of MFV. Despite a subsequent rise in depth of sleep from sleep stage 4 to sleep stage 2 preceding the first REM period, MFV continued decreasing and tended to be lower in sleep stage 2 than in the preceding deep sleep phase (Fig 1). From the first to

Discussion

Computer−assisted TCD offered the unique opportunity to record cerebral hemodynamics on−line, over a time course of seconds, and continuously throughout the entire sleep period in combination with polysomnography. Data presented in this study reveal two main aspects: (1) that the CBFV in patients with SAS is related to the dynamic process of alternating sleep stages and (2) that changes of CBFV not only depend on chemical (Pco2) but also on neuronal (arousal) influences during sleep apnea

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    Presented in part at the “Third International Marburg Symposium on Cardiocirculatory Function during Sleep,” Germany, August 31-September 2, 1994.

    Manuscript received July 26, 1995; revision accepted April 12, 1996.

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