Breathing techniques modulate the magnitude and direction of cerebrospinal fluid flow

2095 

Abstract Submission 

Vidhya Vijayakrishnan Nair¹, Tyler C. Diorio¹, Qiuting Wen², Vitaliy L. Rayz¹, Yunjie Tong¹

¹Purdue University, West Lafayette, IN, ²Indiana University School of Medicine, Indianapolis, IN

Vidhya Vijayakrishnan Nair  
Purdue University
West Lafayette, IN

Tyler C. Diorio  
Purdue University
West Lafayette, IN

Qiuting Wen  
Indiana University School of Medicine
Indianapolis, IN

Vitaliy L. Rayz  
Purdue University
West Lafayette, IN

Yunjie Tong  
Purdue University
West Lafayette, IN

With mounting data indicating the relevance of CSF flow in aiding waste clearance from the brain, as well as potential pathophysiological linkages to neurodegenerative diseases(Braun & Iliff, 2020; Li et al., 2022; Simon & Iliff, 2016), developing effective strategies to enhance CSF flow in the brain is critical. Here, we attempt this using simple, widely-used breathing exercises: paced breathing and breath holding. The existing functional Magnetic Resonance Imaging (fMRI) based approach used in previous studies exclusively records CSF motion in the 4th ventricle in a singular direction, either craniad or caudad, contingent on the positioning of the scan volume(Fultz et al., 2019; Picchioni et al., 2022; Vijayakrishnan Nair et al., 2022, 2023; Yang et al., 2022). This prohibits the evaluation of net CSF flow. Therefore, an additional goal of the current study is to overcome this limitation and reconstruct net CSF movement signals through the use of breathing techniques during the fMRI scans. These challenges act as a unique physiological control condition bridging the unidirectional craniad and caudad CSF signals into net biphasic CSF movements. Furthermore, we also employ a novel methodology(Diorio et al., 2023) to estimate the velocities of these net biphasic CSF movements.

All participants' MRI data were acquired using a 3T SIEMENS MRI scanner with a 64-channel head coil. The scans included structural T1-weighted MPRAGE, and resting state/breathing challenge fMRI. A chest belt was also worn by all participants to record respiration signals. The fMRI scans were carefully designed to capture the craniad/caudad CSF movements respectively from the brain/neck volumes, utilizing the inflow effect. The inflow effect refers to the increase in fMRI signal intensity that occurs when 'fresh' fluid (not exposed to radiofrequency pulses) enters a region of the imaging volume, as demonstrated in figure 1A for various inflow scenarios. The CSF inflow signals were extracted from a suitable voxel at the center of the 4th ventricle by overlaying the fMRI over the structural T1-weighted image registered to the fMRI space (figure 1B and 1C). Further, these unidirectional CSF inflow signals were converted into velocities based on fact that the maximum possible inflow signal increase occurs when the full volume of a given voxel has been "refreshed" with incoming fluid in each repetition time (figure 1A) as well as theoretical considerations from Gao et al. 1988(Gao et al., 1988). Finally, net biphasic velocities were computed by summing the independently captured craniad and caudad unidirectional velocities (figure 1D).

The group averaged time series plots of unidirectional craniad and caudad CSF velocities in the resting state and the net biphasic CSF velocities during the breathing challenges are shown in figure 2. It can be seen that the amplitude of CSF velocity oscillations is much larger during the paced breathing and breath holding challenges in comparison to resting state. In detail, the standard deviation (representing the amplitude variation) of biphasic CSF velocities during breath holding is significantly larger (p-value = 0.02) than the resting state, whereas that of paced breathing is only relatively larger (p-value = 0.85) in comparison to resting state. We also estimate that breath holding challenge generates a net volume displacement of -1.04±1.33 mL in the caudad direction, whereas paced breathing elicits a net volume displacement of 0.28±1.45 mL in the craniad direction, in comparison to a mere 0.16±0.68 mL across the entire duration of the corresponding scans.

Our results demonstrate that these respiratory challenges enhance the magnitude as well as control the direction of CSF movement in the fourth ventricle. We also successfully report our novel approach where we use these breathing challenges as a unique control condition to reconstruct net CSF velocities from independently captured unidirectional inflow signals.

Methods Development ²

Anatomy and Functional Systems ¹

BOLD fMRI

Cerebral Metabolism and Hemodynamics

Neurophysiology of Imaging Signals

Cerebral Blood Flow

Cerebro Spinal Fluid (CSF)

FUNCTIONAL MRI

MRI

Treatment

Other - Breathing Challenges