de Lecea, A. | bioRxiv Science

bioRxiv2026

Three-Dimensional Fluid-Structure Interaction Reveals Trade-offs Among Oxygen Delivery, Shear, and Washout in Pediatric Roller-Pump Cardiopulmonary Bypass

Objective: To determine how roller speed, tubing occlusion, and hematocrit jointly regulate oxygen delivery, shear, and washout in pediatric roller-pump cardiopulmonary bypass. Methods: A three-dimensional, closed-loop fluid-structure interaction model resolved roller-tube contact, tubing deformation, and blood flow. Forty simulations combined 4 roller speeds (38-95 revolutions per minute), 2 occlusion levels (77% and 83%), and 5 hematocrit levels (15%-50%). Cycle-averaged flow, oxygen delivery, peak shear stress, and viscosity-normalized relative residence time were quantified. Results: Roller compression produced retrograde leakage through the occluded gap, localized peak shear stress exceeding 100 pascals, and adjacent stagnation and recirculation. Flow increased nearly linearly with roller speed and was higher at greater occlusion, with little hematocrit dependence. Higher speed and occlusion increased peak shear stress while reducing relative residence time; higher hematocrit further increased peak shear stress. Similar oxygen delivery could arise from substantially different flow environments: among 10 conditions providing oxygen delivery of approximately 9-12 milliliters per minute, peak shear stress ranged from approximately 25 to 70 pascals. Within conditions satisfying an illustrative minimum oxygen-delivery threshold, lower hematocrit permitted speed and occlusion settings yielding lower peak shear stress and relative residence time. Conclusions: Pediatric roller-pump settings that provide similar oxygen delivery can expose blood to markedly different shear and washout environments. Joint evaluation of these metrics may guide selection of speed, occlusion, and hematocrit to meet a target oxygen delivery while reducing shear and improving washout. Keywords: Cardiopulmonary bypass; roller pump; pediatric cardiac surgery; fluid-structure interaction; shear stress; relative residence time

bioengineering↗

bioRxiv2025

Hierarchical and Spatial Mapping of Whole-Brain c-Fos Activity Reveals Distinct Opioid and Withdrawal Neuronal Ensembles

How opioid exposure and withdrawal states shape brain activity at the systems and circuit level remains poorly understood. Here, we use whole-brain, cellular-resolution c-Fos mapping to define brain-wide activity patterns and neuronal ensembles associated with morphine administration and withdrawal. To account for the brains anatomically nested structure, we developed and applied a hierarchical statistical framework that detects region-specific changes in activity and outperforms conventional methods that treat brain regions as individual, unrelated units. These distributed signals formed ensembles with consistent and anatomically structured patterns of activity, both within subregions and across multiple connected brain areas. By combining TRAP2-based activity tagging with acute whole-brain c-Fos staining, we identified morphine- and withdrawal-activated ensembles and found that they are largely non-overlapping at the single-cell level, even within the same brain region. Integration with existing spatial transcriptomics datasets identified molecular markers for these state-specific ensembles in key brain areas such as the nucleus of accumbens, amygdala and ventral tegmental areas. Lastly, by integrating Allen mouse whole-brain transcriptional datasets, we identified the molecular identity of the morphine- administration and withdrawal ensembles. These findings define dissociable neuronal ensembles that encode opposing drug states and introduce a scalable framework for linking whole-brain activity to molecular and circuit-level mechanisms. HighlightsO_LIWhole-brain neural activity mapping identifies the regional and spatial difference of morphine-administration and withdrawal neuronal ensembles. C_LIO_LIBRANCH, a hierarchical statistical testing framework, offers increased sensitivity and anatomical interpretability for whole-brain datasets. C_LIO_LITRAP2-based activity tagging reveals brain-wide separation of acute morphine and withdrawal ensembles at the cellular level. C_LIO_LIA systematic analysis of the whole brain neural activity data combined with spatial transcriptomic data revealed molecular features of opioid-related neural ensembles. C_LI

neuroscience↗