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Biomedical subjects

John L Anderson

Publications and source records attributed to John L Anderson.

9 recordsLinked to original sources
PubMed2007

Repair of recurrent visceral aortic patch aneurysm after thoracoabdominal aortic aneurysm repair with a branched endovascular stent graft.

Aneurysmal degeneration of the visceral aortic patch is an uncommon late complication of surgical replacement of the thoracoabdominal aorta. We report on a 70-year-old woman who had undergone previous open thoracoabdominal aortic aneurysm repair and subsequent revision surgery for a visceral aortic patch aneurysm. The patient presented with a recurrent asymptomatic 60-mm-diameter visceral aortic patch aneurysm involving the celiac axis and superior mesenteric artery. The lesion was successfully treated with a custom-designed Zenith branched endovascular stent graft. The patient remains well at 12 months.

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PubMed2006

Salvage of failed prior endovascular abdominal aortic aneurysm repair with fenestrated endovascular stent grafts.

Three patients with type I proximal endoleak after previous endovascular abdominal aortic aneurysm (AAA) repair were treated with fenestrated endovascular stent grafts. Six renal arteries, three superior mesenteric arteries, and one coeliac axis were targeted for incorporation by graft fenestration. The fenestration-renal ostium interface was secured with balloon-expandable stents and completion angiography demonstrated no endoleaks and antegrade perfusion in all target vessels. All patients made an uncomplicated recovery. Fenestrated endovascular stent grafts can be used to salvage failed prior endovascular AAA repair in patients who are considered unsuitable for other endovascular or open surgical interventions.

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PubMed2005

Movement of colloidal particles in two-dimensional electric fields.

We characterize the movement of carbon black particles in inhomogeneous, two-dimensional dc electric fields. Motivated by display applications, the particles are suspended in a nonpolar solvent doped with a charge control agent. The two-dimensional fields are generated between strip electrodes on a glass slide spaced 120 microm apart with field strengths up to 10(4) V/m. Such fields are insufficient to drive either electrohydrodynamic instabilities or natural convection due to ohmic heating, but they move the particles between the electrodes in about 30 s. In the center region between the strip electrodes, the particles move by electrophoresis; that is, the particle velocity is proportional to the electric field. However, when imposing a constant-potential or constant-current boundary condition at the electrodes to derive the electrical field, the electrophoretic mobility calculated from the measured particle velocities is outside the range of mobilities predicted from the theory of O'Brien and White. Near the electrodes the particles either speed up or slow down, depending on the polarity of the electrode, and these changes in velocity cannot be explained simply by electrophoresis in a spatially varying electric field. We suggest that this anomalous motion arises from electrohydrodynamic flows originating from the interaction between the space charge of the polarized layers above the electrodes and the electric field. Approximate calculations indicate such flows could be sufficiently strong to explain the anomalous trajectories near the edges of the electrodes.

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PubMed2005

Ionic conduction and electrode polarization in a doped nonpolar liquid.

Electrical current versus potential relationships were measured for solutions of dodecane containing the charge control agent poly(isobutylene succinimide) (PIBS) at various concentrations. Both one-dimensional (parallel planar electrodes) and two-dimensional (strip electrodes) fields were studied. The initial current was proportional to the applied voltage for both electrode configurations. Using the initial decay rate of the current (t < 0.5 s) in the planar electrode cell and the Gouy-Chapman model for electrode polarization, we determined the diffusion coefficient of the charge carriers (micelles) in the solution, from which we calculated their effective radius to be 10 nm. The constancy of the carrier radius over a 7-fold change in PIBS concentration, along with the proportionality between conductivity and concentration, supports the hypothesis that the charged species result from the interactions between two micelles. The experimentally determined geometric factor (cell constant) relating current to applied potential at time zero for the strip electrode cell agrees with the value predicted from the solution of Laplace's equation for the electrical potential in this system. The intermediate-time (0.5-3.0 s) decay rate of current was faster than predicted from the classical Gouy-Chapman theory of the double layer, possibly because of volume fraction effects in the double layer. The very long-time (minutes to hours) residual current that we observed is not explained, but we suspect that some charge transfer across the electrode must have occurred because there was insufficient ion capacity (i.e., amount of PIBS) in the solution to account for the total charge transferred through the cell.

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PubMed2005

Repair of juxtarenal para-anastomotic aortic aneurysms after previous open repair with fenestrated and branched endovascular stent grafts.

Three patients with juxtarenal para-anastomotic aortic aneurysms after previous open abdominal aortic aneurysm repair were treated with custom-designed fenestrated and branched Zenith endovascular stent grafts. Six renal arteries and two superior mesenteric arteries were targeted for incorporation by graft fenestrations and branches. The fenestration/renal ostium interface was secured with balloon-expandable Genesis stents (n = 5) or Jostent stent grafts (n = 1). Completion angiography demonstrated no endoleaks and antegrade perfusion in all target vessels. During follow-up, one patient developed asymptomatic renal artery occlusion and underwent further endovascular intervention for type I distal endoleak. Computed tomography at 12 months demonstrated complete aneurysm exclusion in all patients with antegrade perfusion in the remaining target vessels. Fenestrated and branched endovascular stent grafts may be an acceptable alternative to conventional open repair in this group of patients.

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PubMed2005

Repair of thoracoabdominal aortic aneurysms with fenestrated and branched endovascular stent grafts.

OBJECTIVE: To report the repair of thoracoabdominal aortic aneurysms (TAAAs) with fenestrated and branched endovascular stent grafts (EVSGs). METHODS: Four patients with asymptomatic TAAAs were treated with custom-designed Zenith fenestrated and branched EVSGs. Three patients had undergone previous open aortic aneurysm repair. Thirteen visceral vessels in four patients were targeted for incorporation by graft fenestrations and branches. RESULTS: The fenestration/orifice interface was secured with balloon-expandable Genesis stents or Jostent stent grafts in 9 of 13 target vessels. Completion angiography demonstrated antegrade perfusion in 12 of 13 target vessels. One renal artery occluded because of graft rotation during deployment. There were no endoleaks. Three patients required additional surgical procedures related to access vessels. One patient required reoperation for bleeding from an extra-anatomic bypass graft and subsequently died from multisystem organ failure. Three patients made an uncomplicated recovery. No patient developed spinal cord ischemia. Computed tomography at 12 months in the 3 survivors demonstrated complete aneurysm exclusion with antegrade perfusion in all 10 target vessels. CONCLUSIONS: TAAA repair with fenestrated and branched EVSGs is feasible and provides an acceptable and promising alternative to conventional surgical repair in selected patients.

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PubMed2004

Interactions between two bubbles on a hot or cold wall.

A temperature gradient normal to a planar wall produces two-dimensional motion and aggregation or separation of bubbles on the hot or cold wall, respectively. The origin of the motion is fluid convection driven by the thermal Marangoni stress on the surface of the bubbles. Previous theories for the dynamics of two or more bubbles have been based on an analysis of flow about a single bubble and the resulting convection that entrains its neighbors. Here we extend the theory by solving the quasi-steady equations for the temperature and velocity fields for two bubbles. The result is a quantitative model for the relative velocity between two bubbles as a function of both the distance between them and the gap between each bubble and the surface. Interactions between the bubbles strongly increase the approach velocity, which is counter-intuitive because the hydrodynamic resistance increases as the bubbles approach each other. An asymptotic analysis indicates the thermocapillary force bringing them together or pushing them apart is singular in the separation when the bubbles are close to each other. The two-bubble theory agrees reasonably well with the experimentally measured velocities of pairs of bubbles on hot or cold surfaces, though it slightly overestimates the velocities.

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PubMed2002

Two-particle dynamics on an electrode in ac electric fields.

The relative motion between pairs of negatively charged latex particles 9.7 microm in diameter and deposited on an electrode was measured by optical microscopy and image analysis. At an rms field of approximately 30 V cm(-1), the two particles moved toward each other at frequencies below 500 Hz, but they separated at 1000 Hz. In the cases of aggregation, there are several interesting characteristics. First, when the center-to-center separation of a pair was initially 6 particle radii or more apart, a transient 'incubation' period of tens of seconds was observed before the particles began to move toward each other. Second, the two particles never came into contact, rather at long times the pair maintained a stationary gap between them equal to approximately one-half the particle radius. This stationary gap between particles was also observed for the aggregation of clusters of three or more particles. Finally, the rate of approach for a pair of particles decreased as the frequency increased. Larger fields are required to move particles together in ac compared to dc fields; at 30 Hz the ac field must be 130 times greater than the dc field to achieve the same rate of approach. Taking advantage of the qualitative and quantitative differences of the cooperative motion of particles in dc vs. ac fields, one should be able to re-position particles by alternating between these two modes. We demonstrated that the same pair of particles can be brought together at low frequency (100 or 200 Hz) and then separated at high frequency (1000 Hz).

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