Noninvasive determination of brain tissue oxygenation during sleep in obstructive sleep apnea: a near-infrared spectroscopic approach

Abstract

Study objectives: Recurrent apneas and hypoxemia during sleep in obstructive sleep apnea (OSA) are associated with profound changes in cerebral blood flow to the extent that cerebral autoregulation may be insufficient to protect the brain. Since the brain is sensitive to hypoxia, the cerebrovascular morbidity seen in OSA could be due to chronic, cumulative effects of intermittent hypoxia. Near-infrared spectroscopy (NIRS) has the potential to noninvasively monitor brain tissue oxygen saturation (SO2), and changes in concentration of oxyhemoglobin [O2Hb], deoxyhemoglobin [HHb] and total hemoglobin [tHb] with real-time resolution. We hypothesized that brain tissue oxygenation would be worse during sleep in OSA relative to controls and sought to determine the practical use of NIRS in the sleep laboratory.

Design: We evaluated changes in brain tissue oxygenation using NIRS during overnight polysomnography.

Setting: Studies were conducted at University of Illinois, Chicago and Carle Hospital, Urbana, Illinois.

Patients: Nineteen subjects with OSA and 14 healthy controls underwent continuous NIRS monitoring during polysomnography.

Measurements and results: We observed significantly lower indexes of brain tissue oxygenation (SO2: 57.1 +/- 4.9 vs. 61.5 +/- 6.1), [O2Hb]: 22.8 +/- 7.7 vs. 31.5 +/- 9.1, and [tHb]: 38.6 +/- 11.2 vs. 48.6 +/- 11.4 micromol/L) in OSA than controls (all P < 0.05). However, multivariate analysis showed that the differences might be due to age disparity between the two groups.

Conclusions: NIRS is an effective tool to evaluate brain tissue oxygenation in OSA. It provides valuable data in OSA assessment and has the potential to bridge current knowledge gap in OSA.

Figures

Figure 1

Complete Instrument Setup with Optical Probe. Figure 1 shows details of the experimental setup with the measuring optical probes that are placed on the forehead. Two independent channels with 8 laser diodes (4 each in the 690 nm and 830 nm frequency range) are depicted.

Figure 2

Digital Display of Raw Data During NIRS Collection. Figure 2 shows real time raw data as displayed on the PC monitor during NIRS recording. The upper left corner shows instantaneous numerical readout of brain oxygen saturation (StO2], total hemoglobin concentration (THC), oxyhemoglobin concentration (oxy), and deoxyhemoglobin (De-oxy) in the 2 wavelengths on the right (Rt) and left (Lt) forehead. The lower portion of the graph show graphic display of the cumulative trend in absolute values of brain tissue oxygenation indexes over the recording period.

Figure 3

Trend of Oxyhemoglobin and Histogram of Single Average Method. Figure 3 shows trend in brain tissue oxygen saturation during a 6-hour overnight NIRS recording in a study subject in the upper graph. The signal is separated into right (red) and left (green) based on probe location on the forehead. The bottom histogram shows derivation of the single average value of brain tissue oxygen saturation based on over 20,000 data points for the entire night on both sides of the forehead. Similar analysis is done for the other NIRS variables.

Figure 4

Scatter Plots of Four NIRS Outcomes and Age by OSA and Control Group. Scatter plots showing the effect of age on brain tissue oxygenation indexes in the OSA and healthy control groups. A= brain oxygen saturation; B = brain oxyhemoglobin concentration; C= brain deoxyhemoglobin concentration and D= brain total oxyhemoglobin concentration.