Biology subjects

Chan, S.-t.

Publications and source records attributed to Chan, S.-t..

5 recordsLinked to original sources

bioRxiv2021

Correcting Cardiorespiratory Noise in Resting-state Functional MRI Data Acquired in Critically Ill Patients

Resting-state functional MRI (rs-fMRI) is being used to develop diagnostic, prognostic, and therapeutic biomarkers for critically ill patients with severe brain injuries. In studies of healthy volunteers and non-critically ill patients, prospective cardiorespiratory data are routinely collected to remove non-neuronal fluctuations in the rs-fMRI signal during analysis. However, the feasibility and utility of collecting cardiorespiratory data in critically ill patients on a clinical MRI scanner are unknown. We concurrently acquired rs-fMRI (TR=1250ms), cardiac and respiratory data in 23 critically ill patients with acute severe traumatic brain injury (TBI), and 12 healthy control subjects. We compared the functional connectivity results after denoising with cardiorespiratory data (i.e., RETROICOR) with the results obtained after standard bandpass filtering. Rs-fMRI data in 7 patients could not be analyzed due to imaging artifacts. In 6 of the remaining 16 patients (37.5%), cardiorespiratory data were either incomplete or corrupted. In both patients and control subjects, the functional connectivity corrected with RETROICOR did not significantly differ from that corrected with bandpass filtering of 0.008-0.125 Hz. Collectively, these findings suggest that there is a limited feasibility and utility to prospectively acquire high-quality cardiorespiratory data during rs-fMRI in critically ill patients with severe TBI for physiological correction.

neuroscience↗

bioRxiv2021

Cerebrovascular responses to O2-CO2 exchange ratio under brief breath-hold challenge in patients with chronic mild traumatic brain injury

Breath-by-breath O2-CO2 exchange ratio (bER) is a respiratory gas exchange (RGE) metric, which is the ratio of the changes in the partial pressure of O2 ({Delta}PO2) to CO2 ({Delta}PCO2) between endinspiration and end-expiration, has been demonstrated to characterize the cerebrovascular responses to breath-hold challenge in healthy individuals. We aimed to explore if bER could characterize cerebrovascular responses in patients with chronic mild traumatic brain injury (mTBI) under breath-hold challenge. We also investigated the correlation between bER and the severity of post-concussion symptoms. Blood-oxygenation-level-dependent (BOLD) images were acquired using functional magnetic resonance imaging (fMRI) on eleven patients with chronic mTBI and eleven controls without brain injury history when performing a breath-hold task. Time series of RGE metrics of {Delta}PO2, {Delta}PCO2, and bER were computed, and their cross-correlation with regional change in BOLD ({Delta}BOLD) was calculated. Symptom burden was assessed using the Rivermead Post Concussion Questionnaire (RPQ), and its correlation with RGE changes was also measured. Compared with controls, a diffuse decrease in the correlation between regional {Delta}BOLD and bER was found in the brain of mTBI patients (pfdr<0.05). No significant difference was found between patients and controls for the correlation of regional {Delta}BOLD with {Delta}PO2 and {Delta}PCO2. The averaged changes in bER ({rho}=0.79, p=0.01) and {Delta}PO2 ({rho}=0.70, p=0.03) in breath-hold epochs decreased with increased symptom severity indicated by RPQ scores. Our imaging and symptom severity findings suggest that bER can be used to characterize cerebrovascular responses to breath-hold in mTBI patients. RGE may contribute to the post-concussive symptom severity.

neuroscience↗

bioRxiv2019

Functional magnetic resonance imaging of regional impaired cerebrovascular reactivity for migraineurs in the interictal state

There is still an unmet need of mapping the potential impairment of cerebrovascular reactivity (CVR) in episodic migraineurs in the interictal state. We mapped CVR of 6 episodic migraineurs and 5 headache-free controls (HC) with blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) under carbon dioxide (CO2) challenge of 30-second epochs with elevated end-tidal partial pressure of CO2 (PETCO2) by 4-8mmHg. Three migraineurs have migraine without aura (MOA) and the other three have migraine with aura (MA). We found that only MOA subjects showed a reduced or negative BOLD response to CO2 at the red nucleus. All 3 MOA subjects were characterized by bilateral posterior communicating artery hypoplasia (bPCAH) identified by MR angiography (MRA). MOA and HC subjects did not show any significant difference in BOLD responses to CO2 challenge in cortical and white matter while MA subjects showed poor positive association between BOLD responses and PETCO2 in large territories of the cortex and white matter tracts. The combined use of fMRI under CO2 challenge and MRA presented a unique approach to investigate the mechanisms of episodic migraine in the interictal state demonstrating for the first time negative CVR at the red nucleus of the midbrain in patients with MOA. CVR maps obtained from both the midbrain and cortical regions provided various signatures to explore the differences between migraineurs and HC and between MOA and MA.

neuroscience↗

bioRxiv2019

Cerebrovascular reactivity assessment with O2-CO2 exchange ratio under brief breath hold challenge

Hypercapnia during breath holding is believed to be the dominant driver behind the modulation of cerebral blood flow (CBF). Here we showed that the cerebrovascular responses to brief breath hold epochs were coupled not only with increased partial pressure of carbon dioxide (PCO2), but also with a decrease in partial pressure of oxygen (PO2). We used transcranial Doppler ultrasound to evaluate the CBF changes during breath holding by measuring the cerebral blood flow velocity (CBFv) in the middle cerebral arteries, a pair of cerebral arteries that supply most parts of the brain. The regional CBF changes during breath hold epochs were mapped with blood oxygenation level dependent (BOLD) signal changes as surrogate of CBF changes using functional magnetic resonance imaging (fMRI) technique. Given the interdependence of the dynamic changes between PCO2 and PO2, we found that the breath-by-breath O2-CO2 exchange ratio (bER), namely the ratio of changes in PO2 ({Delta}PO2) to changes in PCO2 ({Delta}PCO2) between end inspiration and end expiration, was superior to either {Delta}PO2 or {Delta}PCO2 alone in coupling with the changes of CBFv and BOLD signals under breath hold challenge. The regional cerebrovascular reactivity (CVR) results derived by regressing BOLD signal changes on bER under breath hold challenge resembled those derived by regressing BOLD signal changes on end-tidal partial pressure of CO2 (PETCO2) under exogenous CO2 challenge. Our findings provide a novel insight on the potential of using bER to better quantify CVR changes under breath hold challenge, although the physiological mechanisms of cerebrovascular changes underlying breath hold and exogenous CO2 challenges are potentially different.

neuroscience↗

bioRxiv2019

Dynamic Brain-Body Coupling of Breath-by-Breath O2-CO2 Exchange Ratio with Resting State Cerebral Hemodynamic Fluctuations

The origin of low frequency cerebral hemodynamic fluctuations (CHF) in resting state remains unknown. Here we studied the contribution of respiratory gas exchange (RGE) metrics to CHF during spontaneous breathing. RGE metrics include the breath-by-breath changes of partial pressure of oxygen ({Delta}PO2) and carbon dioxide ({Delta}PCO2) between end inspiration and end expiration, and their ratio breath-by-breath O2-CO2 exchange ratio (bER). We used transcranial Doppler sonography to evaluate CHF changes during spontaneous breathing by measuring the cerebral blood flow velocity (CBFv) in the middle cerebral arteries. The regional CHF changes during spontaneous breathing were mapped with blood oxygenation level dependent (BOLD) signal changes using functional magnetic resonance imaging (fMRI) technique. We found that prominent oscillations with periods of 0.5 to 2 minutes characterized {Delta}PO2, {Delta}PCO2 and bER. The oscillations of bER were coherent with CHF during spontaneous breathing at the frequency range of 0.008-0.03Hz which is consistent with the low frequency resting state CHF. CHF had strong correlation with bER, followed by {Delta}PO2 and then by {Delta}PCO2. Brain regions with the strongest bER-CHF coupling overlapped with many areas of default mode network. Although the physiological mechanisms underlying the strong correlation between bER and CHF are not completely understood, our findings suggest the contribution of bER to low frequency resting state CHF. It also provides a novel insight of brain-body interaction via CHF and oscillations of RGE metrics.

neuroscience↗