Simulation of enhanced deposition due to magnetic field alignment of ellipsoidal particles in a lung bifurcation.

BACKGROUND: Aerosolized chemotherapy has been recognized as a potential treatment for lung cancer. The challenge of providing sufficient therapeutic effects without reaching dose-limiting toxicity levels hinders the development of aerosolized chemotherapy. This could be mitigated by increasing drug-delivery efficiency with a noninvasive drug-targeting delivery method. The purpose of this study is to use direct numerical simulations to study the resulting local enhancement of deposition due to magnetic field alignment of high aspect ratio particles. METHODS: High aspect ratio particles were approximated by a rigid ellipsoid with a minor diameter of 0.5 µm and fluid particle density ratio of 1,000. Particle trajectories were calculated by solving the coupled fluid particle equations using an in-house micro-macro grid finite element algorithm based on a previously developed fictitious domain approach. Particle trajectories were simulated in a morphologically realistic geometry modeling a symmetrical terminal bronchiole bifurcation. Flow conditions were steady inspiratory air flow due to typical breathing at 18 L/min. Deposition efficiency was estimated for two different cases: [1] particles aligned with the streamlines and [2] particles with fixed angular orientation simulating the magnetic field alignment of our previous in vitro study. RESULTS: The local enhancement factor defined as the ratio between deposition efficiency of Case [1] and Case [2] was found to be 1.43 and 3.46 for particles with an aspect ratio of 6 and 20, respectively. CONCLUSIONS: Results indicate that externally forcing local alignment of high aspect ratio particles can increase local deposition considerably.

Differential indication for mechanical circulatory support following heart transplantation.

PURPOSE: We describe our experience with ventricular assist devices (VAD) in patients with cardiogenic shock refractory to pharmacological therapy and support using intraaortic balloon pump after cardiac transplantation. PATIENTS: Between July 1987 and August 1997, 848 patients underwent cardiac transplantation in our hospital. INTERVENTIONS: Fifteen patients (1.8%) needed mechanical circulatory support for refractory cardiac failure due to right heart failure (six patients), primary graft failure (three patients), and acute rejection (six patients). Three pump systems were used: Biomedicus Centrifugal Pump, Abiomed BVS 500, and Thoratec VAD. The choice of system depended on the indication and quality of each device. Seven patients (47%) could be weaned from the mechanical circulatory support (MCS) system and three patients (20%) are long-term survivors. RESULTS: All 15 patients developed at least one serious complication, such as multiorgan failure (MOF), liver failure, acute renal failure or sepsis. Twenty-five per cent had severe bleeding and 13% had neurological complication. Mortality was due mostly to MOF, MOF and sepsis or sepsis. The survivors had a CI greater than 2.2 l.min.m2, total bilirubin less than 1.0 U/1, and did not undergo resuscitation. CONCLUSIONS: Heart failure after cardiac transplantation severe enough to require MCS is currently associated with several major complications and high mortality (80%).