Journal Article

Dynamic brain-body coupling of breath-by-breath O2-CO2 exchange ratio with resting state cerebral hemodynamic fluctuations

Evans, Karleyton C., van der Kouwe, Andre, Kwong, Kenneth K., Zheng, Yong-ping, Ahn, Andrew C., Rosen, Bruce R., Selb, Juliette, Song, Tian-yue, Chan, Suk-tak

2020

Overview

The origin of low frequency cerebral hemodynamic fluctuations (CHF) in the resting state remains unknown. Breath-by breath O2-CO2 exchange ratio (bER) has been reported to correlate with the cerebrovascular response to brief breath hold challenge at the frequency range of 0.008-0.03Hz in healthy adults. bER is defined as the ratio of the change in the partial pressure of oxygen (ΔPO2) to that of carbon dioxide (ΔPCO2) between end inspiration and end expiration. In this study, we aimed to investigate the contribution of respiratory gas exchange (RGE) metrics (bER, ΔPO2 and ΔPCO2) to low frequency CHF during spontaneous breathing. Twenty-two healthy adults were included. We used transcranial Doppler sonography to evaluate CHF by measuring the changes in cerebral blood flow velocity (ΔCBFv) in bilateral middle cerebral arteries. The regional CHF were mapped with blood oxygenation level dependent (ΔBOLD) signal changes using functional magnetic resonance imaging. Temporal features and frequency characteristics of RGE metrics during spontaneous breathing were examined, and the simultaneous measurements of RGE metrics and CHF (ΔCBFv and ΔBOLD) were studied for their correlation. We found that the time courses of ΔPO2 and ΔPCO2 were interdependent but not redundant. The oscillations of RGE metrics were coherent with resting state CHF at the frequency range of 0.008-0.03Hz. Both bER and ΔPO2 were superior to ΔPCO2 in association with CHF while CHF could correlate more strongly with bER than with ΔPO2 in some brain regions. Brain regions with the strongest coupling between bER and ΔBOLD overlapped with many areas of default mode network including precuneus and posterior cingulate. Although the physiological mechanisms underlying the strong correlation between bER and CHF are unclear, our findings suggest the contribution of bER to low frequency resting state CHF, providing a novel insight of brain-body interaction via CHF and oscillations of RGE metrics.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Adult / Adults / Arteries / Biology and Life Sciences / Blood / Blood flow / Blood Flow Velocity - physiology / Brain / Brain - physiology / Brain mapping / Brain research / Breathing / Carbon dioxide / Carbon Dioxide - blood / Carbon dioxide exchange / Cerebral blood flow / Cerebrovascular Circulation - physiology / Cerebrovascular system / Correlation / Correlation analysis / Cortex (parietal) / Coupling / Female / Flow velocity / Fluctuations / Frequency ranges / Functional magnetic resonance imaging / Gas exchange / Gases / Healthy Volunteers / Hemodynamics / Hemodynamics - physiology / Humans / Low frequencies / Magnetic resonance / Magnetic resonance imaging / Magnetic Resonance Imaging - methods / Male / Medicine and Health Sciences / Metabolism / Middle Cerebral Artery - physiology / Neuroimaging / Oscillations / Oxygen / Oxygen - blood / Oxygenation / Partial Pressure / Physical Sciences / Physiology / Research and Analysis Methods / Respiration / Respiratory Rate - physiology / Rest - physiology / Temporal variability / Temporal variations / Ultrasonography, Doppler, Transcranial - methods / Ultrasound / Vasodilation - physiology