Predictors of changes in cerebral perfusion and oxygenation during obstructive sleep apnea

Abstract

Obstructive sleep apnea syndrome (OSAS) is a common sleep disorder. Severe OSAS defined as apnea-hypopnea index (AHI) ≥ 30/h is a risk factor for developing cerebro-cardiovascular diseases. The mechanisms of how repetitive sleep apneas/hypopneas damage cerebral hemodynamics are still not well understood. In this study, changes in blood volume (BV) and oxygen saturation (StO2) in the left forehead of 29 newly diagnosed severe OSAS patients were measured by frequency-domain near-infrared spectroscopy during an incremental continuous positive airway pressure (CPAP) titration protocol together with polysomnography. The coefficients of variation of BV (CV-BV) and the decreases of StO2 (de-StO2) of more than 2000 respiratory events were predicted using linear mixed-effect models, respectively. We found that longer events and apneas rather than hypopneas induce larger changes in CV-BV and stronger cerebral desaturation. Respiratory events occurring during higher baseline StO2 before their onsets, during rapid-eye-movement sleep and those associated with higher heart rate induce smaller changes in CV-BV and de-StO2. The stepwise increased CPAP pressures can attenuate these changes. These results suggest that in severe OSAS the length and the type of respiratory event rather than widely used AHI may be better parameters to indicate the severity of cerebral hemodynamic changes.

Figure 1

The histogram of the durations of the respiratory events under the measurements without CPAP (n = 884) and with the CPAP (n = 1873). 55 events longer than 60 s during titration are not shown.

Figure 2

The samples of near-infrared spectroscopy (NIRS) changes in obstructive sleep apneas and hypopneas. The dash lines indicate the start and the end of the events. The cerebral desaturations (de-StO2) are marked in the three events. BV is blood volume. a.u. is arbitrary unit.

Figure 3

The distributions of the coefficient of variation (CV) of cerebral blood volume (BV) and the decrease of cerebral StO2 (de-StO2). Changes in CV of BV and de-StO2 are correlated as shown in (A). The box plot suggests the outliers of CV of BV are larger than 3% and the cut-off 3% is marked with the dash line in its distribution (B). Similarly, the cut-off for outliers is 8.7% as shown in the box plot of de-StO2 and it is marked with the dash line in the distribution (C).

Figure 4

The changes in the coefficient of variation (CV) of cerebral blood volume (BV) and the decrease of cerebral tissue oxygen saturation (StO2) versus the duration of events in each patient. The data points of different colors indicate data from different patients, and the lines of different colors are the linear fitting of the data points. The black line is the mean of all patients. We only show the events of durations shorter than 60 s, considering that only a minority of events is longer than 60 s and they may be outliers that can bias the fitting trends.