Showing papers by "Robert H. Bartlett published in 2006"
TL;DR: The future of ECLS will include improvements in devices accompanied by circuit simplification and auto-regulation, which will allow application of EFLS to populations currently excluded from such support; for example, thromboresistant circuits will eliminate the need for systemic anticoagulation and lead to the use of this technique in premature newborns.
52 citations
TL;DR: Although not currently in clinical practice, liquid ventilation using perfluorocarbons to provide gas exchange in the lungs is a potentially useful adjunct in the management of severe respiratory failure.
Abstract: Acute respiratory distress syndrome (ARDS) has many underlying causes and carries an overall mortality of 40 to 60%. For those patients with severe ARDS who have a predicted mortality of 80 to 100%, extracorporeal life support (ECLS) can provide an extraordinary means of support. We recently demonstrated a survival to hospital discharge of 52% in this subset of patients. ECLS is capable of providing full respiratory and cardiac support, allowing time for the patient to recover from the underlying disease process. Additionally, ventilator settings are reduced to "rest" settings, avoiding the consequences of ventilator-induced lung injury that can contribute to a worse outcome. Systemic heparinization is a mainstay of ECLS therapy because of platelet activation in the circuit. Mechanical complications and significant bleeding can occur in up to one quarter of patients, requiring close attention and prompt intervention should they occur. Although not currently in clinical practice, liquid ventilation using perfluorocarbons to provide gas exchange in the lungs is a potentially useful adjunct in the management of severe respiratory failure.
24 citations
TL;DR: The results show that pulsatile flow improves the gas transfer to the fluid compared to steady flow and the degree of enhancement is found to be significant when the oscillation frequency is large, when the void fraction of the fiber bundle is decreased, and when the Reynolds number is increased.
Abstract: The pulsatile flow and gas transport of a Newtonian passive fluid across an array of cylindrical microfibers are numerically investigated. It is related to an implantable, artificial lung where the blood flow is driven by the right heart. The fibers are modeled as either squared or staggered arrays. The pulsatile flow inputs considered in this study are a steady flow- with a sinusoidal perturbation and a cardiac flow. The aims of this study are twofold: identifying favorable array geometry/spacing and system conditions that enhance gas transport; and providing pressure drop data that indicate the degree of flow resistance or the demand on the right heart in driving the flow through the fiber bundle. The results show that pulsatile flow improves the gas transfer to the fluid compared to steady flow. The degree of enhancement is found to be significant when the oscillation frequency is large, when the void fraction of the fiber bundle is decreased, and when the Reynolds number is increased; the use of a cardiac flow input can also improve gas transfer. In terms of array geometry, the staggered array gives both a better gas transfer per fiber (for relatively large void fraction) and a smaller pressure drop (for all cases). For most cases shown, an increase in gas transfer is accompanied by a higher pressure drop required to power the flow through the device.
24 citations
TL;DR: In this article, the mass transport of a pulsatile free-stream flow past a single circular cylinder is investigated as a building block for an artificial lung device, where the free stream far from the cylinder is represented by a time-periodic (sinusoidal) component superimposed on a steady velocity.
Abstract: The mass transport of a pulsatile free-stream flow past a single circular cylinder is investigated as a building block for an artificial lung device The free stream far from the cylinder is represented by a time-periodic (sinusoidal) component superimposed on a steady velocity The dimensionless parameters of interest are the steady Reynolds number (Re), Womersley parameter (α), sinusoidal amplitude (A), and the Schmidt number (Sc) The ranges investigated in this study are 5⩽Re⩽40, 025⩽α⩽4, 025⩽A⩽075, and Sc=1000 A pair of vortices downstream of the cylinder is observed in almost all cases investigated These vortices oscillate in size and strength as α and A are varied For α αc, the vortex is attached to the cylinder only during part of a time cycle (intermittent) The time-averaged Sherwood number, Sh, is found to be largely influenced by the steady Reynolds number, increasing approximately as
19 citations
TL;DR: The ideal C for right ventricular function is at least 0.5 ml/mm Hg and may be as high as 5 ml/ mm Hg to minimize septal shift, and results indicate the PS 0th harmonic input impedance modulus was not affected by C.
Abstract: This study examined the effect of artificial lung compliance (C) on pulmonary system (PS) impedance and right ventricular function during in-series attachment of the MC3 Biolung in adult sheep. Compliances, C, of 0-20 ml/mm Hg were tested at the Biolung inlet. Results indicate the PS 0 harmonic input impedance modulus was not affected by C. The PS first harmonic input impedance modulus (Z1) was 10.9 +/- 3.2 mm Hg/(l/min) at C = 0 ml/mm Hg and minimized to 2.41 +/- 0.79 mm Hg/(l/min) at C > or = 0.5 ml/mm Hg. Cardiac output was 58% +/- 10% of its pre-Biolung attachment, baseline value at C = 0 ml/mm Hg and was maximized to an average of 75% +/- 11% at C > or = 0.5 ml/mm Hg. The left ventricular lateral-to-anteroposterior axis length ratio, which decreases with leftward septal shift, increased with C from 0.52 +/- 0.12 at C = 0 ml/mm Hg to 0.76 +/- 0.06 at C = 5 ml/mm Hg (p 5 ml/mm Hg. Therefore, the ideal C for right ventricular function is at least 0.5 ml/mm Hg and may be as high as 5 ml/mm Hg to minimize septal shift.
18 citations
TL;DR: Findings regarding the parameter range for vortex formation may provide principles for designing artificial lungs to enhance convective mixing and can be used to mimic the flow not only in TALs but in other physiological systems.
Abstract: 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.
15 citations
TL;DR: Initiation of ECLS in infants <10 kg should not be delayed unnecessarily to perform preservative reduction or to utilize PRBC units of a specific age, as hyperkalemia of the primed EClS circuit is not associated with systemic hyperkAlemia in the patient post-initiation ofECLS.
Abstract: Objective: To assess the risk of hyperkalemia with blood-primed extracorporeal life support (ECLS) circuits in infants < 10 kg.Design: Retrospective cohort study of all neonatal and pediatric patients <10 kg placed on ECLS from May 1998 to April 2001.Measurements and main results: Data collection including patient weight, patient potassium levels pre- and post-initiation of ECLS, potassium level of the primed ECLS circuit, age of the packed red blood cell (PRBC) unit, type of preservative, and preservative reduction status. Seventy-six circuits were available for the analysis. The age of the PRBC unit and preservative reduction status significantly affected the potassium level of the primed ECLS circuit. Multivariate linear regression analysis showed no significant effect on the post-ECLS initiation patient potassium level with respect to the PRBC age, the preservative reduction status, the patient potassium level prior to ECLS initiation, and the potassium level of the primed ECLS circuit.Conclusions: In...
8 citations
TL;DR: The AV model was deemed to be superior due to its simplicity, ability for filter modeling, and decrease in intensive monitoring, but both models are excellent designs for nonthrombogenic surface testing.
Abstract: To identify nonthrombogenic devices to be used in extracorporeal circulation (ECC), an efficient, small animal model is required Initially, a venovenous (VV) model in rabbits was designed for this purpose and was a good representation of ECC Technical difficulties in the VV model led to the development of a more simplistic arteriovenous (AV) model Anesthetized, tracheotomized, 3-kg rabbits were used for both models Circuits were constructed of PVC tubing The VV model used 8-Fr umbilical artery catheters for both drainage and reinfusion, and the AV model used a 14-GA angiocatheter for carotid artery access and a 10-Fr thoracic catheter for venous access The AV model included a chamber to mimic oxygenator or filter modeling Hourly measurements included blood gases, platelet counts, and fibrinogen levels for the 4-hour studies The VV ECC groups demonstrated platelet consumption like that seen in the clinical arena The AV model demonstrated the same with or without additional surface area within the chamber The AV model was deemed to be superior due to its simplicity, ability for filter modeling, and decrease in intensive monitoring However, both models are excellent designs for nonthrombogenic surface testing
8 citations
2 citations
TL;DR: Dr. Robert H. Bartlett offers answers to questions about how his work on ECMO began, the reaction of the critical care community to the use of ECMO, and how challenges in studying ECMO in clinical trials have been approached.
2 citations
01 Jan 2006