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W J Ohley

Publications and source records attributed to W J Ohley.

8 recordsLinked to original sources
PubMed2001

Fractal analysis of bone X-ray tomographic microscopy projections.

Fractal analysis of bone X-ray images has received much interest recently for the diagnosis of bone disease. In this paper, we propose a fractal analysis of bone X-ray tomographic microscopy (XTM) projections. The aim of the study is to establish whether or not there is a correlation between three-dimensional (3-D) trabecular changes and two-dimensional (2-D) fractal descriptors. Using a highly collimated beam, 3-D bone X-ray tomographic images were obtained. Trabecular bone loss was simulated using a mathematical morphology method. Then, 2-D projections were generated in each of the three orthogonal directions. Finally, the model of fractional Brownian motion (fBm) was used on bone XTM 2-D projections to characterize changes in bone structure that occur during disease, such a simulation of bone loss. Results indicate that fBm is a robust texture model allowing quantification of simulations of trabecular bone changes.

Bone and Bones↗
PubMed1999

Hemodynamic effects of new intra-aortic balloon counterpulsation timing methods in patients: a multicenter evaluation.

BACKGROUND: To test whether later intra-aortic balloon pump (IABP) deflation approaching or simultaneous with left ventricular ejection would improve hemodynamics and myocardial efficiency with the use of new balloon deflation methods, 4 IABP timing techniques were evaluated in 43 patients. METHODS AND RESULTS: Later balloon deflation produced significantly greater percentage changes in mean aortic pressure (6% vs 1%), systolic pressure time index (-27% vs -20%), diastolic pressure time index (35% vs 19%), and the systolic pressure-time index/diastolic pressure-time index ratio (97% vs 51%), respectively. However, these changes increased peak systolic pressure (-15% vs -11%). Cardiac output and stroke volume indexes were not significantly altered over the 4 settings. CONCLUSIONS: These data suggest that systemic hemodynamics and myocardial efficiency may be improved by later balloon deflation approaching left ventricular ejection in comparison to conventional IABP timing.

Adult↗
PubMed1984

The intraaortic balloon pump: a nonlinear digital computer model.

A computer based model for in-series cardiac assistance by intraaortic balloon pumping was developed in this study. The model, obtained from the Navier-Stokes and Continuity equations, was capable of computing pressures, volumetric flow rates and radii through the arterial system. The model was used to study the effects of a wide range of assist device timing adjustments on the benefits of ventricular assistance under conditions corresponding to those measured during animal experiments. The model was also used to study the relationship between device timing adjustments and the benefits of ventricular assistance under constant cardiovascular state conditions. Such studies are important in isolating the response of the system to assist device phasing from the response associated with system state. The results obtained in this study demonstrate that the hemodynamic response of the cardiovascular system to intraaortic balloon pumping is a sensitive function of both the state of the cardiovascular system and phasing of the assist device.

Animals↗
PubMedDate not supplied

Influence of catheter and arterial diameter on flow distal to an intra-aortic balloon insertion site: a theoretic examination and in vitro assessment.

Percutaneous placement of an intra-aortic balloon (IAB) through a femoral artery of a patient is associated with a risk of reduction of blood flow distal to the balloon insertion site. If this reduction is severe, it ultimately causes limb ischemia and necessitates IAB removal. Although clinicians intuitively know that larger catheters cause higher flow restrictions, very few studies have examined this situation quantitatively. The authors theoretically analyzed the insertion site geometry in relationship to the catheter diameter and other factors effecting distal flow. To verify the findings, in vitro flow tests were conducted with various IAB catheters currently available on the market, as well as their respective sheaths and hemostasis plugs. This was done using a blood analog solution in an array of polyvinyl chloride tubing sizes. Diameters of the vessel and catheter have a profound and nonlinear effect on the distal flow. For example, a 12.2 Fr catheter in a 0.187 in. vessel only allows 19.9% of normal flow, whereas a 6.1 Fr catheter in the same size vessel allows a 92.0% flow. As the catheter diameter increases, the physical resistance suddenly grows, which causes a significant drop in distal flow. These results are accurately predicted by a mathematical model that gives flow percentage results to within 15% of those measured experimentally. In general, vessels larger than 5 mm in diameter do not exhibit substantial flow reduction for most IABs with and without sheaths. In smaller vessels, however, this reduction may be significant. Sheathless insertion is extremely effective in improving distal blood flow in such a situation. Hemostasis plugs restrict the distal flow similar to respective sheaths, thus diminishing the benefits of sheathless insertion.

Catheterization↗