Biology subjects

Greene, C. L.

Publications and source records attributed to Greene, C. L..

3 recordsLinked to original sources

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↗

bioRxiv2023

Dysphagia as a missing link between post-surgical- and opioid-related pneumonia

ObjectivePostoperative pneumonia remains a common complication of surgery, despite increased attention. The purpose of our study was to determine the effects of routine surgery and post-surgical opioid administration on airway protection risk. MethodsEight healthy adult cats were evaluated for dysphagia in 2 experiments. 1) In 4 female cats airway protection status was tracked following routine abdominal surgery (spay surgery) plus low-dose opioid administration (buprenorphine 0.015mg/kg, IM, q8-12h; n=5). 2) Using a cross-over design (2 male, 2 female) cats were treated with moderate (0.02mg/kg) or high (0.04mg/kg) dose buprenorphine (IM, q8-12h; n=5) to determine changes in airway protection status or evidence of dysphagia. ResultsAirway protection was significantly affected in both experiments, but most severely post-surgically where 75% of the animals exhibited silent aspiration. ConclusionOropharyngeal swallow is impaired by the partial mu-opioid receptor agonist buprenorphine, most remarkably in the post-operative setting. These findings have implications for the prevention and management of aspiration pneumonia in vulnerable populations.

physiology↗

bioRxiv2021

Laryngeal and swallow dysregulation following acute cervical spinal cord injury

Proper function of the larynx is vital to airway protection, including swallow. While the swallow reflex is controlled by the brainstem, patients with cervical spinal cord injuries (cSCI) are likely at increased risk of disordered swallow (dysphagia) and pneumonia, and the underlying mechanisms are unknown. We aimed to determine if acute spinal cord injury would disrupt swallow function in animal models. We hypothesized that 1) loss of descending efferent information to the diaphragm would affect swallow and breathing differently, and that 2) loss of ascending spinal afferent information would alter central swallow regulation to change motor drive to the upper airway. We recorded amplitudes of laryngeal and inspiratory muscle electromyograms (EMGs), submental and pharyngeal muscle EMGs, and cardiorespiratory measures in freely breathing pentobarbital-anesthetized cats and rats. First, we assessed the effect of a lateral hemisection at the second cervical level (C2) in cats during breathing. Posterior cricoarytenoid (laryngeal abductor) EMG activity during inspiration increased nearly two-fold, indicating that inspiratory laryngeal drive increased following cSCI. Ipsilateral to the injury, the crural diaphragm EMG was significantly reduced during breathing (62 {+/-} 25 percent change post-injury), but no animal had a complete termination of all activity; 75% of animals had an increase in contralateral diaphragm recruitment after cSCI, but this did not reach significance. Next, we assessed the effect of C2 lateral hemisection in cats during swallow. The thyroarytenoid (laryngeal adductor) and thyropharyngeus (pharyngeal constrictor) both increased EMG activity during swallow, indicating increased upper airway drive during swallow following cSCI. There was no change in the number of swallows stimulated per trial. We also found that diaphragm activity during swallow (schluckatmung) was bilaterally suppressed after lateral C2 hemisection, which was unexpected because this injury did not suppress contralateral diaphragm activity during breathing. Swallow-breathing coordination was also affected by cSCI, with more post-injury swallows occurring during early expiration. Finally, because we wanted to determine if the chest wall is a major source of feedback for laryngeal regulation, we performed T1 total transections in rats. As in the cat C2 lateral hemisection, a similar increase in inspiratory laryngeal activity (posterior cricoarytenoid) was the first feature noted after rat T1 complete spinal cord transection. In contrast to the cat C2 lateral hemisection, diaphragmatic respiratory drive increased after T1 transection in every rat (215 {+/-} 63 percent change), and this effect was significant. Overall, we found that spinal cord injury alters laryngeal drive during swallow and breathing, and alters swallow-related diaphragm activity. Our results show behavior-specific effects, suggesting that swallow may be more affected than breathing is by cSCI, and emphasizing the need for additional studies on laryngeal function during breathing and swallow after spinal cord injury.

neuroscience↗