RESUMEN
Hollow fiber artificial lungs are increasingly being used for long-term applications. However, clot formation limits their use to 1-2 weeks. This study investigated the effect of nitric oxide generating (NOgen) hollow fibers on artificial lung thrombogenicity. Silicone hollow fibers were fabricated to incorporate 50 nm copper particles as a catalyst for NO generation from the blood. Fibers with and without (control) these particles were incorporated into artificial lungs with a 0.1 m(2) surface area and inserted in circuits coated tip-to-tip with the NOgen material. Circuits (N = 5/each) were attached to rabbits in a pumpless, arterio-venous configuration and run for 4 h at an activated clotting time of 350-400 s. Three control circuits clotted completely, while none of the NOgen circuits failed. Accordingly, blood flows were significantly higher in the NOgen group (95.9 ± 11.7, p < 0.01) compared to the controls (35.2 ± 19.7; mL/min), and resistance was significantly higher in the control group after 4 h (15.38 ± 9.65, p < 0.001) than in NOgen (0.09 ± 0.03; mmHg/mL/min). On the other hand, platelet counts and plasma fibrinogen concentration expressed as percent of baseline in control group (63.7 ± 5.7%, 77.2 ± 5.6%; p < 0.05) were greater than those in the NOgen group (60.4 ± 5.1%, 63.2 ± 3.7%). Plasma copper levels in the NOgen group were 2.8 times baseline at 4 h (132.8 ± 4.5 µg/dL) and unchanged in the controls. This study demonstrates that NO generating gas exchange fibers could be a potentially effective way to control coagulation inside artificial lungs.
Asunto(s)
Órganos Artificiales , Pulmón/patología , Óxido Nítrico/metabolismo , Trombosis/metabolismo , Ingeniería de Tejidos/métodos , Animales , Recuento de Células Sanguíneas , Plaquetas/metabolismo , Cobre/sangre , Fibrinógeno/metabolismo , Hemodinámica , Pulmón/irrigación sanguínea , Pulmón/ultraestructura , Conejos , Flujo Sanguíneo Regional , S-Nitrosotioles/metabolismo , Factores de TiempoRESUMEN
Nitric oxide (NO) generating (NOGen) materials have been shown previously to create localized increases in NO concentration by the catalytic decomposition of blood S-nitrosothiols (RSNO) via copper (Cu)-containing polymer coatings and may improve extracorporeal circulation (ECC) hemocompatibility. In this work, a NOGen polymeric coating composed of a Cu°-nanoparticle (80 nm)-containing hydrophilic polyurethane (SP-60D-60) combined with the intravenous infusion of an RSNO, S- nitroso-N-acetylpenicillamine (SNAP), is evaluated in a 4 h rabbit thrombogenicity model and the anti-thrombotic mechanism is investigated. Polymer films containing 10 wt.% Cu°-nanoparticles coated on the inner walls of ECC circuits are employed concomitantly with systemic SNAP administration (0.1182 µmol/kg/min) to yield significantly reduced ECC thrombus formation compared to polymer control + systemic SNAP or 10 wt.% Cu NOGen + systemic saline after 4 h blood exposure (0.4 ± 0.2 NOGen/SNAP vs 4.9 ± 0.5 control/SNAP or 3.2 ± 0.2 pixels/cm² NOGen/saline). Platelet count (3.9 ± 0.7 NOGen/SNAP vs 1.8 ± 0.1 control/SNAP or 3.0 ± 0.2 × 108/ml NOGen/saline) and plasma fibrinogen levels were preserved after 4 h blood exposure with the NOGen/SNAP combination vs either the control/SNAP or the NOGen/saline groups. Platelet function as measured by aggregometry (51 ± 9 NOGen/SNAP vs 49 ± 3% NOGen/saline) significantly decreased in both the NOGen/SNAP and NOGen/saline groups while platelet P-selectin mean fluorescence intensity (MFI) as measured by flow cytometry was not decreased after 4 h on ECC to ex vivo collagen stimulation (26 ± 2 NOGen/SNAP vs 29 ± 1 MFI baseline). Western blotting showed that fibrinogen activation as assessed by Aγ dimer expression was reduced after 4 h on ECC with NOGen/SNAP (68 ± 7 vs 83 ± 3% control/SNAP). These results suggest that the NOGen polymer coating combined with SNAP infusion preserves platelets in blood exposure to ECCs by attenuating activated fibrinogen and preventing platelet aggregation. These NO-mediated platelet changes were shown to improve thromboresistance of the NOGen polymer-coated ECCs when adequate levels of RSNOs are present.
Asunto(s)
Circulación Extracorporea , Óxido Nítrico/química , Polímeros/química , S-Nitrosotioles/química , S-Nitrosotioles/metabolismo , Animales , Western Blotting , Fibrinógeno/metabolismo , Citometría de Flujo , Técnica del Anticuerpo Fluorescente , Humanos , ConejosRESUMEN
Total liquid ventilation (TLV) has the potential to provide respiratory support superior to conventional mechanical ventilation (CMV) in the acute respiratory distress syndrome (ARDS). However, laboratory studies are limited to trials in small animals for no longer than 4 hours. The objective of this study was to compare TLV and CMV in a large animal model of ARDS for 24 hours. Ten sheep weighing 53 ± 4 (SD) kg were anesthetized and ventilated with 100% oxygen. Oleic acid was injected into the pulmonary circulation until PaO2:FiO2 ≤ 60 mm Hg, followed by transition to a protective CMV protocol (n = 5) or TLV (n = 5) for 24 hours. Pathophysiology was recorded, and the lungs were harvested for histological analysis. Animals treated with CMV became progressively hypoxic and hypercarbic despite maximum ventilatory support. Sheep treated with TLV maintained normal blood gases with statistically greater PO2 (p < 10(-9)) and lower PCO2 (p < 10(-3)) than the CMV group. Survival at 24 hours in the TLV and CMV groups were 100% and 40%, respectively (p < 0.05). Thus, TLV provided gas exchange superior to CMV in this laboratory model of severe ARDS.
Asunto(s)
Ventilación Liquida , Respiración Artificial , Insuficiencia Respiratoria/terapia , Animales , Modelos Animales de Enfermedad , Hemodinámica , Humanos , Ventilación Liquida/instrumentación , Ventilación Liquida/métodos , Pulmón/patología , Pulmón/fisiopatología , Intercambio Gaseoso Pulmonar , Síndrome de Dificultad Respiratoria/terapia , Insuficiencia Respiratoria/patología , Insuficiencia Respiratoria/fisiopatología , OvinosRESUMEN
Nitric oxide (NO) has been shown to reduce thrombogenicity by decreasing platelet and monocyte activation by the surface glycoprotein, P-selectin and the integrin, CD11b, respectively. In order to prevent platelet and monocyte activation with exposure to an extracorporeal circulation (ECC), a nitric oxide releasing (NORel) polymeric coating composed of plasticized polyvinyl chloride (PVC) blended with a lipophilic N-diazeniumdiolate was evaluated in a 4 h rabbit thrombogenicity model using flow cytometry. The NORel polymer significantly reduced ECC thrombus formation compared to polymer control after 4 h blood exposure (2.8 +/- 0.7 NORel vs 6.7 +/- 0.4 pixels/cm(2) control). Platelet count (3.4 +/- 0.3 NORel vs 2.3 +/- 0.3 x 10(8)/ml control) and function as measured by aggregometry (71 +/- 3 NORel vs 17 +/- 6% control) were preserved after 4 h exposure in NORel versus control ECC. Plasma fibrinogen levels significantly decreased in both NORel and control groups. Platelet P-selectin mean fluorescence intensity (MFI) as measured by flow cytometry was attenuated after 4 h on ECC to ex vivo collagen stimulation (27 +/- 1 NORel vs 40 +/- 2 MFI control). Monocyte CD11b expression was reduced after 4 h on ECC with NORel polymer (87 +/- 14 NORel vs 162 +/- 30 MFI control). These results suggest that the NORel polymer coatings attenuate the increase in both platelet P-selectin and monocytic CD11b integrin expression in blood exposure to ECCs. These NO-mediated platelet and monocytic changes were shown to improve thromboresistance of these NORel-polymer-coated ECCs for biomedical devices.
Asunto(s)
Circulación Extracorporea , Monocitos/citología , Monocitos/efectos de los fármacos , Óxido Nítrico/metabolismo , Activación Plaquetaria/efectos de los fármacos , Cloruro de Polivinilo/farmacología , Adsorción/efectos de los fármacos , Animales , Antígeno CD11b/metabolismo , Modelos Animales de Enfermedad , Citometría de Flujo , Hemodinámica/efectos de los fármacos , Humanos , Receptores de Lipopolisacáridos/metabolismo , Adhesividad Plaquetaria/efectos de los fármacos , Recuento de Plaquetas , Pruebas de Función Plaquetaria , Conejos , Trombosis/patología , Trombosis/fisiopatología , Factores de TiempoRESUMEN
Negative pressure generated during the expiratory phase of total liquid ventilation (TLV) may induce airway collapse. Evaluation of the effect of repeated airway collapse is crucial to optimize this technique. A total of 24 New Zealand White rabbits were randomly divided into four groups. Ventilation was performed for 6 hours with different strategies: conventional gas ventilation, TLV without airway collapse, and TLV with collapse induced in either 75 or 150 sequential breaths. In the treated groups, airway collapse was induced by increasing the perfluorocarbon drainage velocity while maintaining the minute ventilation constant. Airway pressure, gas exchange, and blood pressure were monitored at 30-minute intervals. At the end of the experiment, airway and lung parenchyma specimens were processed for light microscopy. No evidence of fluorothorax was noticed in any of the four groups at autopsy examination. Minimal signs of inflammation were noticed in all airway and lung parenchyma specimens, but no evident structural alteration was visible. Adequate gas exchange and systemic blood pressure were maintained during all the studies. Repeated airway collapse is not associated with structural changes in the respiratory system and does not alter the gas exchange ability of the lungs.
Asunto(s)
Fluorocarburos/uso terapéutico , Ventilación Liquida/métodos , Atelectasia Pulmonar/patología , Atelectasia Pulmonar/terapia , Animales , Presión Sanguínea , Intercambio Gaseoso Pulmonar , Conejos , Distribución Aleatoria , Pruebas de Función RespiratoriaRESUMEN
The effect of viscosity on the distribution of perfluorocarbon instilled into the lungs for liquid ventilation was investigated. Perfluorocarbon (either perfluorodecalin or FC-3283) was instilled into the trachea during ventilation at a constant infusion rate of 40 ml/min and radiographic images were obtained at 30 frames/s. Image analysis was performed and the homogeneity index of the distribution was computed for images at the end of inspiration of each breath to evaluate the evolution of perfluorocarbon distribution during filling. The higher viscosity perfluorocarbon (perfluorodecalin) resulted in a more homogeneous distribution. This was attributed to perfluorodecalin's higher propensity to form liquid plugs in large airways and to those plugs leaving behind a thicker liquid layer as they propagated through the lungs.
Asunto(s)
Fluorocarburos/química , Fluorocarburos/farmacocinética , Ventilación Liquida/métodos , Pulmón/química , Pulmón/metabolismo , Animales , Difusión , Fluorocarburos/administración & dosificación , Tasa de Depuración Metabólica , Conejos , Distribución Tisular , ViscosidadRESUMEN
The focus of this study is an experimental apparatus that serves as a model for studying blood flow in a total artificial lung (TAL), a prototype device intended to serve as a bridge to lung transplantation or that supports pulmonary function during the treatment of severe respiratory failure. The TAL consists of hollow cylindrical fibers that oxygen-rich air flows through and oxygen-poor blood flows around. Because gas diffusivity in the TAL is very small, a convection mechanism dominates the gas transport, which is why we focus on the velocity around the fibers (modeled as a 0.05-cm-in-diameter and 5-cm-long cylinder). We designed a low-speed water tunnel to study the flow mechanism around the cylinder, across which the flow is generated by a linear actuator that allows different flow patterns to mimic the flow in a TAL. We tested the flow in the test section by numerical simulation and by the particle image velocimetry method to study the flow profile. The results show a uniform flow near the centerline of the water tunnel where the cylinder is placed. This decreases the effects of free-stream turbulence in the shear layers and reduces the uncertainty in determining the flow patterns around the cylinder. Knowledge gained from the flow around one cylinder (fiber) is beneficial for understanding vortex formation around multiple cylinders. We present a summary of vortex formation behind a cylinder for Reynolds numbers (Re) of 1, 3, and 5 and Stokes numbers (Ns) of 0.18 to 0.37; results show that higher Re and Ns favor vortex formation. These findings regarding the parameter range for vortex formation may provide principles for designing artificial lungs to enhance convective mixing. We anticipate that the pulsatile flow circuit presented here can be used to mimic the flow not only in TALs but in other physiological systems.
Asunto(s)
Órganos Artificiales , Modelos Cardiovasculares , Circulación Pulmonar/fisiología , Flujo Pulsátil/fisiología , Animales , Velocidad del Flujo Sanguíneo/fisiología , Diseño de Equipo , Humanos , Bombas de Infusión , Pulmón/irrigación sanguínea , Pulmón/fisiología , Reproducibilidad de los Resultados , AguaRESUMEN
The effects of end-inspiratory lung volume (EILV) and expiratory flow rate (Q) on the location of flow limitation in liquid-filled lungs were investigated by measuring pressure along the airways and by radiographic imaging. The lungs of New Zealand white rabbits were filled with perfluorocarbon to the randomly selected EILV of 20, 30, or 40 ml/kg, and the volume was actively drained at one of three Q: 2.5, 5.0, or 7.5 ml/s. The minimum pressures recorded by a movable catheter at locations along the airways show that flow limitation occurred in the main bronchi and trachea, and was independent of EILV and Q. The minimum pressure at the trachea was -80 mm Hg compared with values that were more positive than -10 mm Hg at a location 3 cm distal to the carina for all EILV and Q combinations. This location was confirmed by the lung images. The airway diameters gradually decreased with time, until flow limitation occurred. In airways distal to the collapse, there was not a significant decrease in diameter. Based on these data, we conclude that flow limitation in liquid-filled lungs occurs in the trachea and main bronchi and its location is independent of EILV or Q.
Asunto(s)
Ventilación Liquida , Pulmón/fisiología , Animales , Ingeniería Biomédica , Flujo Espiratorio Forzado/fisiología , Capacidad Inspiratoria/fisiología , Pulmón/diagnóstico por imagen , Conejos , Radiografía , Mecánica Respiratoria , ReologíaRESUMEN
Flow limitation during pressure-driven expiration in liquid-filled lungs was examined in intact, euthanized New Zealand white rabbits. The aim of this study was to further characterize expiratory flow limitation during gravitational drainage of perfluorocarbon liquids from the lungs, and to study the effect of perfluorocarbon type and negative mouth pressure on this phenomenon. Four different perfluorocarbons (PP4, perfluorodecalin, perfluoro-octyl-bromide, and FC-77) were used to examine the effects of density and kinematic viscosity on volume recovered and maximum expiratory flow. It was demonstrated that flow limitation occurs during gravitational drainage when the airway pressure is < or = -15 cm H(2)O, and that this critical value of pressure did not depend on mouth pressure or perfluorocarbon type. The perfluorocarbon properties affect the volume recovered, maximum expiratory flow, and the time to drain, with the most viscous perfluorocarbon (perfluorodecalin) taking the longest time to drain and resulting in lowest maximum expiratory flow. Perfluoro-octyl-bromide resulted in the highest recovered volume. The findings of this study are relevant to the selection of perfluorocarbons to reduce the occurrence of flow limitation and provide adequate minute ventilation during total liquid ventilation.
Asunto(s)
Ventilación Liquida , Animales , Ingeniería Biomédica , Drenaje Postural , Femenino , Fluorocarburos , Flujo Espiratorio Forzado , Técnicas In Vitro , Mediciones del Volumen Pulmonar , Masculino , Conejos , ViscosidadRESUMEN
Flow limitation in liquid-filled lungs is examined in intact rabbit experiments and a theoretical model. Flow limitation ("choked" flow) occurs when the expiratory flow reaches a maximum value and further increases in driving pressure do not increase the flow. In total liquid ventilation this is characterized by the sudden development of excessively negative airway pressures and airway collapse at the choke point. The occurrence of flow limitation limits the efficacy of total liquid ventilation by reducing the minute ventilation. In this paper we investigate the effects of liquid properties on flow limitation in liquid-filled lungs. It is found that the behavior of liquids with similar densities and viscosities can be quite different. The results of the theoretical model, which incorporates alveolar compliance and airway resistance, agrees qualitatively well with the experimental results. Lung compliance and airway resistance are shown to vary with the perfluorocarbon liquid used to fill the lungs. Surfactant is found to modify the interfacial tension between saline and perfluorocarbon, and surfactant activity at the interface of perfluorocarbon and the native aqueous lining of the lungs appears to induce hysteresis in pressure-volume curves for liquid-filled lungs. Ventilation with a liquid that results in low viscous resistance and high elastic recoil can reduce the amount of liquid remaining in the lungs when choke occurs, and, therefore, may be desirable for liquid ventilation.
Asunto(s)
Fluorocarburos/química , Ventilación Liquida/métodos , Pulmón/fisiología , Modelos Biológicos , Mecánica Respiratoria/fisiología , Reología/métodos , Volumen de Ventilación Pulmonar/fisiología , Resistencia de las Vías Respiratorias/fisiología , Animales , Simulación por Computador , Rendimiento Pulmonar/fisiología , Presión , ConejosRESUMEN
OBJECTIVE: A functional total liquid ventilator should be simple in design to minimize operating errors and have a low priming volume to minimize the amount of perfluorocarbon needed. Closed system circuits using a membrane oxygenator have partially met these requirements but have high resistance to perfluorocarbon flow and high priming volume. To further this goal, a single piston prototype ventilator with a low priming volume and a new high-efficiency hollow-fiber oxygenator in a circuit with a check valve flow control system was developed. DESIGN: Prospective, controlled animal laboratory study. SETTING: Research facility at a university medical center. SUBJECTS: Seven anesthetized, paralyzed, normal New Zealand rabbits INTERVENTIONS: The prototype oxygenator, consisting of cross-wound silicone hollow fibers with a surface area of 1.5 m2 with a priming volume of 190 mL, was tested in a bench-top model followed by an in vivo rabbit model. Total liquid ventilation was performed for 3 hrs with 20 mL.kg(-1) initial fill volume, 17.5-20 mL.kg(-1) tidal volume, respiratory rate of 5 breaths/min, inspiratory/expiratory ratio 1:2, and countercurrent sweep gas of 100% oxygen. MEASUREMENTS AND MAIN RESULTS: Bench top experiments demonstrated 66-81% elimination of CO2 and 0.64-0.76 mL.min(-1) loss of perfluorocarbon across the fibers. No significant changes in PaCO2 and PaO2 were observed. Dynamic airway pressures were in a safe range in which ventilator lung injury or airway closure was unlikely (3.6 +/- 0.5 and -7.8 +/- 0.3 cm H2O, respectively, for mean peak inspiratory pressure and mean end expiratory pressure). No leakage of perfluorocarbon was noted in the new silicone fiber gas exchange device. Estimated in vivo perfluorocarbon loss from the device was 1.2 mL.min(-1). CONCLUSIONS: These data demonstrate the ability of this novel single-piston, nonporous hollow silicone fiber oxygenator to adequately support gas exchange, allowing successful performance of total liquid ventilation.
Asunto(s)
Ventilación Liquida/instrumentación , Oxigenadores , Intercambio Gaseoso Pulmonar , Animales , Sustitutos Sanguíneos/uso terapéutico , Diseño de Equipo , Femenino , Fluorocarburos/uso terapéutico , Masculino , Modelos Animales , Estudios Prospectivos , ConejosRESUMEN
Expiratory flow limitation occurs during total liquid ventilation (TLV), and is characterized by the sudden development of excessively negative intratracheal pressures without increases in flow. The purpose of this study was to identify a dynamic signal for the servoregulation of expiratory flow (Ve), by determining the range of dynamic intratracheal pressures [P(T)], which mark the onset of flow limitation during liquid expiration, where choke occurs at the critical pressure (Pc). The lungs of rabbits were filled with perflurocarbon to an end-inspiratory lung volume (EILV) of 20, 30, or 40cc/kg and connected to a piston driven liquid ventilator, which removed perfluorocarbon at a rate (Vs) of 2.5, 5.0, or 7.5 ml/s. Nine animals per EILV group were used (27 animals total), and within each EILV group each (Vs) was used three times. P(T) and (Ve) (T) were measured at the tracheostomy tube, and dP/dT was calculated from P(T). Pc was determined within each EILV/(Vs) group by examining the average dP/dT curve for the first significant change from baseline. Pc ranged from -6.02 +/- 1.83 to -9.02 +/- 3.2 mm Hg. In general, the higher the EILV, the more negative the Pc. We conclude that Pc during TLV varies within a limited range in rabbits. These data may be used to maximize expired volume during TLV by sequentially tapering flow rates as this critical range of pressures is approached.