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Fernando Casas

Publications and source records attributed to Fernando Casas.

8 recordsLinked to original sources
PubMed2006

Symplectic splitting operator methods for the time-dependent Schrodinger equation.

We present a family of symplectic splitting methods especially tailored to solve numerically the time-dependent Schrodinger equation. When discretized in time, this equation can be recast in the form of a classical Hamiltonian system with a Hamiltonian function corresponding to a generalized high-dimensional separable harmonic oscillator. The structure of the system allows us to build highly efficient symplectic integrators at any order. The new methods are accurate, easy to implement, and very stable in comparison with other standard symplectic integrators.

Journal Article↗
PubMed2006

Development and testing of portable pump for the induction of profound hypothermia in a Swine model of lethal vascular injuries.

UNLABELLED: Rapid induction of a profound hypothermic state (suspended animation) can maintain viability of key organs during repair of lethal injuries. Conventional cardiopulmonary bypass equipment (roller pump) used to induce and reverse hypothermia is expensive, bulky, requires standard electricity, and is not transportable. Development of a small, portable, battery operated, disposable, pump can logistically facilitate induction and maintenance of hypothermia. In this experiment, a portable prototype pump was tested and its performance was compared with the regular roller pump in a swine model of lethal vascular injuries. METHODS: Uncontrolled hemorrhage was induced in 16 swine (80-120 lbs) by creating an iliac artery and vein injury (nonlethal). After 30 minutes of pulseless shock, the descending thoracic aorta was lacerated (lethal injury). Through a left thoracotomy approach, a catheter was placed in the aorta and cold organ preservation solution was infused to rapidly (2 degrees C/min) induce hypothermia (10 degrees C) for 60 minutes. The performance of the prototype pump was initially tested in a nonsurvival experiment (four animals). Then, 12 animals were cooled either with (n = 6/group) (1) conventional roller pump or (2) small prototype pump. The injuries were repaired during hypothermic arrest and the animals were re-warmed (0.5 degrees C/min). Whole blood was infused during resuscitation on cardiopulmonary bypass. Surviving animals were closely monitored for 3 weeks for postoperative complications, neurologic deficits, and organ dysfunction. RESULTS: The flow rates and the time needed to induce and reverse profound hypothermia were no different between the prototype and the conventional roller pumps. Three-week survival rates were 83% in both groups. Only a transient increase in liver enzymes, and markers of cellular injury (creatine kinase, lactate dehydrogenase) was noted (no meaningful difference between groups), with no long-term organ dysfunction. CONCLUSIONS: In this large animal model of lethal vascular injuries, a portable, battery operated, disposable, rotary pump performed as well as the conventional roller pump. The logistical advantages of this system make it an attractive choice for inducing hypothermia in emergency departments and austere settings, and for maintaining hypothermia during transport.

Animals↗
PubMed2005

A portable cardiopulmonary bypass/extracorporeal membrane oxygenation system for the induction and reversal of profound hypothermia: feasibility study in a Swine model of lethal injuries.

The Cleveland Clinic Foundation's (CCF) cardiopulmonary bypass/extracorporeal membrane oxygenation (CPB/ECMO) system capabilities were tested in a hypothermia trauma management feasibility study in a porcine animal model at the Uniformed Services University of the Health Sciences (USUHS, Bethesda, MD, U.S.A.). In this survival series, the CCF system was used in a simulated forward lines combat casualty application where lethal uncontrolled hemorrhage from major vascular injuries was repaired under a state of profound hypothermic arrest (suspended animation), followed by recovery and monitoring in an intensive care unit (ICU) setting. The animals were monitored for survival, neurological impact, cognitive functions, organ damage, and delayed complications over 3 weeks. A survival rate of 83% matched rates previously found using conventional equipment. Neurological findings, organ dysfunction, and complication rates also were no different from previous studies using standard equipment. Successful survival results demonstrated that the CCF CPB/ECMO system could be used to induce a period of profound hypothermic arrest for the repair of lethal traumatic injuries. The logistical advantages of this system make it an attractive choice for use in austere settings and during transport.

Animals↗
PubMed2004

Effects of sodium nitroprusside in aortic stenosis associated with severe heart failure: pressure-volume loop analysis using a numerical model.

In the recently published clinical study [Use of Nitroprusside in Left Ventricular Dysfunction and Obstructive Aortic Valve Disease (UNLOAD)], sodium nitroprusside (SNP) improved cardiac function in patients with severe aortic stenosis (AS) and left ventricular (LV) systolic dysfunction. We explored the possible mechanisms of these findings using a series of numerical simulations. A closed-loop lumped parameters model that consists of 24 differential equations relating pressure and flow throughout the circulation was used to analyze the effects of varying hemodynamic conditions in AS. Hemodynamic data from UNLOAD study subjects were used to construct the initial simulation. Systemic vascular resistance (SVR), heart rate, and aortic valve area were directly entered into the model while end-systolic and end-diastolic pressure-volume (P-V) relationships were adjusted using previously published data to match modeled and observed end-systolic and end-diastolic pressures and volumes. Initial simulation of SNP treatment by a reduction of SVR was not adequate. To obtain realistic model hemodynamics that reliably reproduce SNP treatment effects, we performed a series of simulations while simultaneously changing end-systolic elastance (E(es)), end-systolic volume at zero pressure (V(0)), and diastolic P-V shift. Our data indicate that either an E(es) increase or V(0) decrease is necessary to obtain realistic model hemodynamics. In five patients, we corroborated our findings by using the model to duplicate individual P-V loops obtained before and during SNP treatment. In conclusion, using a numerical model, we identified ventricular function parameters that are responsible for improved hemodynamics during SNP infusion in AS with LV dysfunction.

Aortic Valve Stenosis↗
PubMed2004

Preload-adjusted right ventricular maximal power: concept and validation.

Right ventricular (RV) maximal power (PWR(mx)) is dependent on preload. The objective of this study was to test our hypothesis that the PWR(mx) versus end-diastolic volume (EDV) relationship, analogous to the load-independent stroke work (SW) versus EDV relationship (preload-recruitable SW, PRSW), is linear, with the PWR x-axis intercept (V(0PWR)) corresponding to the PRSW intercept (V(0SW)). If our hypothesis is correct, the preload sensitivity of PWR(mx) could be eliminated by adjusting for EDV and V(0PWR). Ten dogs were instrumented with a pulmonary flow probe, micromanometers, and RV conductance catheter. Data were obtained during bicaval occlusions under various conditions and fitted to PWR(mx) = a.(EDV - V(0PWR))(beta), where a is the slope of the relationship. The PWR(mx) versus EDV relationship did not deviate from linearity (beta = 1.09, P = not significant vs. 1), and V(0PWR) correlated with V(0SW) (r = 0.93, P <0.0001). V(0PRW) was related to steady-state EDV and left ventricular end-diastolic pressure, allowing for estimation of V(0PWR) (V(0Est)) and single-beat PWR(mx) preload adjustment. Dividing PWR(mx) by the difference of EDV and V(0PWR) (PAMP(V0PWR)) eliminated preload dependency down to 50% of the baseline EDV. PWR(mx) adjustment using V(0Est) (PAMP(V0Est)) showed similar preload independency. Enhancing contractility increased PAMP(V0PWR) and PAMP(V0Est) from 176 +/- 52 to 394 +/- 205 W/ml x 10(4) and 145 +/- 51 to 404 +/- 261 W/ml x 10(4), respectively, accompanied by an increase of PRSW from 13.0 +/- 4.5 to 29.7 +/- 16.4 mmHg (all P <0.01). PAMP(V0PWR) and PAMP(V0Est) correlated with PRSW (r = 0.85; r = 0.77; both P <0.001). Numerical modeling confirmed the accuracy of our experimental data. Thus preload adjustment of PWR(mx) should consider a linear PWR(mx) versus EDV relationship with distinct V(0PWR). PAMP(V0PWR) is a preload-independent estimate of RV contractility that may eventually be determined noninvasively.

Animals↗
PubMedDate not supplied

Performance and reliability of the CPB/ECMO Initiative Forward Lines Casualty Management System.

The Cleveland Clinic Foundation CPB/ECMO Initiative Forward Casualty Management System is an economical, compact, transportable, disposable system designed to permit a rapid expansion of trauma management services requiring cardiopulmonary bypass (CPB) or extracorporeal membrane oxygenation (ECMO) pulmonary support. The system, composed of a rotary blood pump, a pump motor driver, and an electronic control console as the blood pumping subsystem, also includes commonly used compatible commercial oxygenators, venous reservoirs, and cannulae. In vitro durability testing accumulated over 100 hours without failure. In vivo reliability was tested in 10 calves under general anesthesia during 6 hours of CPB and ECMO under full heparinization at nominal operating conditions of 4-5 l/min and 2-4 l/min blood flow respectively, and mean arterial pressures between 65 and 100 mm Hg. A mean time to failure of 57 hours was reached during the animal series. Results of these test series demonstrated that this system has the capability to reliably operate during a 6-hour conventional CPB or ECMO procedure, while providing flexibility and ease of use for the operator.

Animals↗
PubMedDate not supplied

MagScrew TAH: an update.

The MagScrew Total Artificial Heart (TAH) system is the result of a close collaboration among the Cleveland Clinic Foundation, Foster Miller Technologies, Wilson Greatbatch Ltd, and Whalen Biomedical Inc. The system components are the thoracic blood pumping unit with attached compliance chamber and refill port, implantable electronic control unit, implantable battery pack, transcutaneous energy transmission system, external battery pack, and a telemetry system for communication with the electronic control unit. System in vitro tests are underway for system characterization and durability demonstration, whereas in vivo tests were conducted to evaluate system performance and biocompatibility under physiologic conditions. The passively filling pump uses a left master alternate left and right ejection control mode and has a Starling law-like response to venous pressure. The in vitro tests documented excellent hydraulic pump performance with high device output of over 9 l/min at left atrial pressures below 12 mm Hg. Atrial balance was well maintained under all test conditions. The in vivo tests demonstrated good biocompatibility without use of anticoagulant therapy. Experimental durations have ranged between 0 and 92 days. Postexplant evaluation of tissue samples did not reveal any sign of thromboembolic events or tissue damage due to device operation.

Animals↗