Cumming School of Medicine
Department of Radiology

Author Of 1 Presentation

Imaging Oral Presentation

FC03.04 - Investigating the temporal relationship between inflammation and fdNIRS-measured hypoxia in an MS population  

Speakers
Presentation Number
FC03.04
Presentation Topic
Imaging
Lecture Time
13:36 - 13:48

Abstract

Background

Previously, we used frequency domain near-infrared spectroscopy (fdNIRS), a non-invasive imaging modality, to show that brain hypoxia exists in a subset of MS patients. Currently, there is limited knowledge on the effects of hypoxia in MS. However, some studies suggest that hypoxia may exacerbate inflammation of the central nervous system (CNS). It is important to elucidate the time-course of hypoxia in relation to inflammation to further understand its role in MS.

Objectives

The aim of the present study was to use fdNIRS to determine if hypoxia in MS resolves quickly or if it is a chronic condition.

Methods

We used fdNIRS to quantify cortical microvasculature hemoglobin saturation (StO2) in 55 controls and 85 MS patients. StO2 values that were 2 standard deviations (SD) below the control mean were defined as hypoxic (<55.7%). Arterial oxygen saturation (SaO2) was measured using a pulse oximeter to confirm that reduced StO2 was not systemic in origin. To determine whether the temporal pattern of StO2 relates to changes in acute CNS inflammation, we recruited a subset of MS patients (hypoxic: n=12; normoxic: n=7) for a longitudinal study. We measured StO2 once a week for 4 consecutive weeks, and then once a month for 5 subsequent months. Due to COVID-19-related lab closures, we were only able to obtain StO2 data for the first 8 weeks for 13 of these patients (hypoxic: n=8; normoxic: n=5).

Results

StO2 in MS patients was significantly lower compared to controls (57.6±7.6% vs. 62.3±3.6%, respectively, p=0.002), with no differences in SaO2. For the longitudinal study, we found that StO2 values for normoxic and hypoxic MS groups did not change significantly over the course of 8 weeks (F (9, 36.9) =1.44, p=0.255).

Conclusions

To our knowledge, we are the first group to use fdNIRS to identify a subset of MS patients who experience persistent brain hypoxia. As hypoxia in MS patients persists beyond 4 weeks, we argue that it can present as a chronic condition. This indicates that, in these patients, physiological responses such as angiogenesis have not occurred or are not sufficient to result in resolution of hypoxia. With such chronic hypoxia we would predict that in these patients, some symptoms may be a result of this chronic hypoxia. Also, we argue that such chronic hypoxia could exacerbate and further stimulate a pathological immune response (a hypoxia inflammation cycle).

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Author Of 1 Presentation

Imaging Poster Presentation

P0563 - Could light scattering measured with frequency domain near-infrared spectroscopy provide new information on cerebral edema in MS? (ID 1220)

Speakers
Presentation Number
P0563
Presentation Topic
Imaging

Abstract

Background

Studies utilizing frequency-domain near-infrared spectroscopy (fdNIRS) have demonstrated that approximately 30% of multiple sclerosis (MS) patients have brain hypoxia. The effects of hypoxia on these individuals, however, are yet to be fully elucidated. Literature shows that hypoxia can induce cerebral edema, characterized by an increase in brain water content, and mitochondrial swelling. This phenomenon can be detected using NIRS technology as an increase in light scattering and may provide extensive insight into MS pathology.

Objectives

The aim of our study was to determine if there are differences in light scattering and absorbance as measured by fdNIRS (OxiplexTS Frequency Domain Near-Infrared Spectrometer, ISS, USA) between controls and MS patients

Methods

fdNIRS measurements were obtained from the frontal cortex of 54 controls and 83 MS patients. The parameters measured included hemoglobin saturation in tissue microvasculature (StO2), scattering coefficient (μs) and absorption coefficient (μa) at 690 and 824 nm. Light scattering and absorption values were averaged across wavelengths. Each parameter was compared between controls and MS patients using a Student’s t-test.

Results

As previously shown, we found that in MS patients, StO2 percentage was significantly lower than in controls (57.40±7.66 vs. 61.28±6.27, respectively, p=0.002). The mean light scattering (μs) in the MS population was significantly higher than controls (9.25±1.36cm-1 vs. 8.65±1.34cm-1, respectively, p=0.015), with no differences in the mean absorbance (μa) (0.11±0.02cm-1 vs. 0.11±0.02cm-1, respectively, p=0.99).

Conclusions

We report that reduced StO2 in MS patients occurs alongside an increase in light scattering with no detected difference in absorbance. These results resemble a prior study investigating NIRS parameters on acute mountain sickness, which demonstrated that an increase in light scattering without changes in absorption is indicative of hypoxia-induced cerebral edema. Cerebral edema may also be associated with mitochondrial dysfunction, which in conjunction with pre-existing hypoxia, may contribute to detrimental brain damage. Previously, we used fdNIRS to confirm the presence of hypoxia in MS. This study shows it may also be a useful tool to investigate consequential cerebral edema and or mitochondrial integrity in MS.

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