NASA Bioscience and Engineering Institute at the University of Michigan

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76168/1/AIAA-2005-134-865.pd

Point-Of-Care Echocardiography And Electrocardiography In Assessing Suspected Pulmonary Embolism

POINT-OF-CARE ECHOCARDIOGRAPHY AND ELECTROCARDIOGRAPHY IN ASSESSING SUSPECTED PULMONARY EMBLOSIM. John Grotberg, James Daley, Richard A. Taylor, Chris L. Moore. Section of Ultrasound, Department of Emergency Medicine, Yale University, School of Medicine, New Haven, CT. Daniels and TwiST electrocardiogram (ECG) scores have been proposed to detect right heart strain (RHS). Tricuspid Annular Plane Systolic Excursion (TAPSE) is a reliable indicator of RHS in patients with acute pulmonary embolism (PE). I aimed to investigate the relationship between these ECG scores, TAPSE, and the level of care required for patients with acute PE. This was a prospective observational study of 110 patients undergoing CTA for suspected PE. ECGs were obtained and patients underwent bedside echocardiography. Low TAPSE was defined as ≤17 mm. Mean Daniels and TwiST scores were compared to mean TAPSE, and all were used to evaluate the risk of requiring “PE elevated care” (PEEC), defined as care more aggressive than simple heparination. Mean Daniels and TwiST scores were significantly different between low and high TAPSE groups (p\u3c0.0001), and high Daniels and TwiST scores correlated to low TAPSE (p\u3c0.0001, p=0.0002). PE positive (PE+) patients had lower mean TAPSE than PE negative (PE-) patients (p=0.0003). PE+ patients had a higher mean Daniels score and mean TwiST score than PE- patients (p=0.0024, p=0.0033). Patients requiring PEEC had lower mean TAPSE (p=0.047) and higher mean TwiST (p=0.020) values. TAPSE ≤17 mm and TwiST ≥5 had increased risks of 6.9 (p=0.045) and 4.4 (p=0.025) respectively for requiring PEEC. Both the Daniels and TwiST ECG scores correlated with TAPSE. All three were predictive of PE on CTA, while TAPSE and TwiST were predictive of requiring PEEC, suggesting their prognostic value in PE care

Preface: Biofluid mechanics

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87903/2/031401_1.pd

The steady propagation of a surfactant-laden liquid plug in a two-dimensional channel

In this study, we investigate the steady propagation of a liquid plug in a two-dimensional channel lined by a uniform, thin liquid film. The liquid contains soluble surfactant that can exist both in the bulk fluid and on the air-liquid interface. The Navier-Stokes equations with free-surface boundary conditions and the surfactant transport equations are solved using a finite volume numerical scheme. The adsorption/desorption process of the surfactant is modeled based on pulmonary surfactant properties. As the plug propagates, the front meniscus sweeps preexisting interfacial surfactant from the precursor film, and the surfactant accumulates on the front meniscus interface. As the front meniscus converges on the precursor film from the region where the interfacial surfactant concentration is maximized, the Marangoni stress opposes the flow. In this region, the Marangoni stress results in nearly zero surface velocity, which causes the precursor film thickness near the meniscus to be thicker than the leading film thickness. Since the peaks of wall pressure and wall shear stress occur due to narrowing of the film thickness, the observed increase of the minimum film thickness weakens these stresses. In the thicker film region, however, the drag forces increase due to an increase in the surfactant concentration. This causes the overall pressure drop across the plug to increase as a result of the increasing surfactant concentration. A recirculation flow forms inside the plug core and is skewed toward the rear meniscus as the Reynolds number increases. When no surfactant exists, the recirculation flow is in contact with both the front and the rear interfaces. As the surfactant concentration increases, the Marangoni stress begins to rigidify the front interface and forces the recirculation flow away from the front interface. Subsequently, the recirculation flow is directed away from the rear interface in a manner similar to that for the front interface. When the plug length is shorter, this change in recirculation pattern occurs at a smaller surfactant concentration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87308/2/082102_1.pd

The effect of gravity on liquid plug propagation in a two-dimensional channel

The effect of plug propagation speed and gravity on the quasisteady motion of a liquid plug in a two-dimensional liquid-lined channel oriented at an angle αα with respect to gravity is studied. The problem is motivated by the transport of liquid plugs instilled into pulmonary airways in medical treatments such as surfactant replacement therapy, drug delivery, and liquid ventilation. The capillary number Ca is assumed to be small, while the Bond number Bo is arbitrary. Using matched asymptotic expansions and lubrication theory, expressions are obtained for the thickness of the trailing films left behind by the plug and the pressure drop across it as functions of Ca, Bo, αα and the thickness of the precursor films. When the Bond number is small it is found that the trailing film thickness and the flow contribution to the pressure drop scale as Ca2/3Ca2∕3 at leading order with coefficients that depend on Bo and αα. The first correction to the film thickness is found to occur at O(Ca)O(Ca) compared to O(Ca4/3)O(Ca4∕3) in the Bo = 0Bo=0 case. Asymmetry in the liquid distribution is quantified by calculating the ratio of liquid volumes above and below the centerline of the channel, VṘ. VR = 1VR=1 at Bo = 0Bo=0, indicating a symmetric distribution, and decreases with Bo and Ca, but increases with the plug length LpLp. The decrease of VRVR with Ca suggests that higher propagation speeds in small airways may result in less homogenous liquid distribution, which is in contrast to the expected effect in large airways. For given values of the other parameters, a maximum capillary number CacCac is identified above which the plug will eventually rupture. When the Bond number becomes equal to an orientation-dependent critical value BocBoc, it is found that the scaling of the film thickness and pressure drop change to Ca1/2Ca1∕2 and Ca1/6Ca1∕6, respectively. It is shown that this scaling is valid for small increments of the Bond number over its critical value, Bo = Boc+BCa1/6Bo=Boc+BCa1∕6, but for higher Bond numbers the asymptotic approach breaks down.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87914/2/031507_1.pd

The propagation of a surfactant laden liquid plug in a capillary tube

This paper considers the propagation of a liquid plug, forced by a driving pressure ΔP, within a rigid tube. The tube is already lined with a liquid precursor film of thickness 2.h̄2. Both the plug and the precursor film, as well as the interface, contain small amounts of surfactant whose concentrations are assumed to be near equilibrium. Since the motions are slow, we seek asymptotic solutions for small capillary number, Ca≪1,Ca≪1, and also assume that sorption kinetics control the surfactant flux to the interface compared to bulk diffusion. An additional asymptotic assumption is that the Stanton number, St, is sufficiently large such that β∝Ca1/3/St≪1,β∝Ca1/3/St≪1, which relates the importance of sorption kinetics to convection. The surfactant strength is measured by the surface elasticity, E = M/βE=M/β where M is the Marangoni number. The results of the analysis are that, for a given plug Ca, ΔP increases with increasing E but decreases with increasing 2.h̄2. The trailing film thickness, 1,h̄1, increases with ΔP, but at a slower rate when E is larger. For 1<2,h̄1<h̄2, criteria for plug rupture are established. This model is relevant to delivery of surfactants into the lung by direct instillation into the bronchial network as is done in surfactant replacement therapy and the use of surfactant solutions to carry other substances (e.g., genetic material) into the airways. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69965/2/PHFLE6-14-2-471-1.pd

The Propagation of a Liquid Bolus Through an Elastic Tube and Airway Reopening

We use lubrication theory and matched asymptotic expansions to model the quasi-steady propagation of a liquid bridge through an elastic tube. In the limit of small capillary number, asymptotic expressions are found for the pressure drop across the bridge and the thickness of the liquid film left behind, as functions of the capillary number, the thickness of the liquid lining ahead of the bridge and the elastic characteristics of the tube wall. For a given precursor thickness, we find a critical propagation speed, and hence a critical imposed pressure drop, above which the bridge will eventually burst, and hence the tube will reopen

Management of severe acute respiratory distress syndrome: A primer

This narrative review explores the physiology and evidence-based management of patients with severe acute respiratory distress syndrome (ARDS) and refractory hypoxemia, with a focus on mechanical ventilation, adjunctive therapies, and veno-venous extracorporeal membrane oxygenation (V-V ECMO). Severe ARDS cases increased dramatically worldwide during the Covid-19 pandemic and carry a high mortality. The mainstay of treatment to improve survival and ventilator-free days is proning, conservative fluid management, and lung protective ventilation. Ventilator settings should be individualized when possible to improve patient-ventilator synchrony and reduce ventilator-induced lung injury (VILI). Positive end-expiratory pressure can be individualized by titrating to best respiratory system compliance, or by using advanced methods, such as electrical impedance tomography or esophageal manometry. Adjustments to mitigate high driving pressure and mechanical power, two possible drivers of VILI, may be further beneficial. In patients with refractory hypoxemia, salvage modes of ventilation such as high frequency oscillatory ventilation and airway pressure release ventilation are additional options that may be appropriate in select patients. Adjunctive therapies also may be applied judiciously, such as recruitment maneuvers, inhaled pulmonary vasodilators, neuromuscular blockers, or glucocorticoids, and may improve oxygenation, but do not clearly reduce mortality. In select, refractory cases, the addition of V-V ECMO improves gas exchange and modestly improves survival by allowing for lung rest. In addition to VILI, patients with severe ARDS are at risk for complications including acute cor pulmonale, physical debility, and neurocognitive deficits. Even among the most severe cases, ARDS is a heterogeneous disease, and future studies are needed to identify ARDS subgroups to individualize therapies and advance care

The effect of age and demographics on rib shape

Elderly populations have a higher risk of rib fractures and other associated thoracic injuries than younger adults, and the changes in body morphology that occur with age are a potential cause of this increased risk. Rib centroidal path geometry for 20 627 ribs was extracted from computed tomography (CT) scans of 1042 live adult subjects, then fitted to a six‐parameter mathematical model that accurately characterizes rib size and shape, and a three‐parameter model of rib orientation within the body. Multivariable regression characterized the independent effect of age, height, weight, and sex on the rib shape and orientation across the adult population, and statistically significant effects were seen from all demographic factors (P < 0.0001). This study reports a novel aging effect whereby both the rib end‐to‐end separation and rib aspect ratio are seen to increase with age, producing elongated and flatter overall rib shapes in elderly populations, with age alone explaining up to 20% of population variability in the aspect ratio of mid‐level ribs. Age was not strongly associated with overall rib arc length, indicating that age effects were related to shape change rather than overall bone length. The rib shape effect was found to be more strongly and directly associated with age than previously documented age‐related changes in rib angulation. Other demographic results showed height and sex being most strongly associated with rib size, and weight most strongly associated with rib pump‐handle angle. Results from the study provide a statistical model for building rib shapes typical of any given demographic by age, height, weight, and sex, and can be used to help build population‐specific computational models of the thoracic rib cage. Furthermore, results also quantify normal population ranges for rib shape parameters which can be used to improve the assessment and treatment of rib skeletal deformity and disease.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137729/1/joa12632_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137729/2/joa12632.pd