Linear-Nonlinear Stiffness Responses of Carbon Fiber-Reinforced Polymer Composite Materials and Structures: A Numerical Study.

The stiffness response or load-deformation/displacement behavior is the most important mechanical behavior that frequently being utilized for validation of the mathematical-physical models representing the mechanical behavior of solid objects in numerical method, compared to actual experimental data. This numerical study aims to investigate the linear-nonlinear stiffness behavior of carbon fiber-reinforced polymer (CFRP) composites at material and structural levels, and its dependency to the sets of individual/group elastic and damage model parameters. In this regard, a validated constitutive damage model, elastic-damage properties as reference data, and simulation process, that account for elastic, yielding, and damage evolution, are considered in the finite element model development process. The linear-nonlinear stiffness responses of four cases are examined, including a unidirectional CFRP composite laminate (material level) under tensile load, and also three multidirectional composite structures under flexural loads. The result indicated a direct dependency of the stiffness response at the material level to the elastic properties. However, the stiffness behavior of the composite structures depends both on the structural configuration, geometry, lay-ups as well as the mechanical properties of the CFRP composite. The value of maximum reaction force and displacement of the composite structures, as well as the nonlinear response of the structures are highly dependent not only to the mechanical properties, but also to the geometry and the configuration of the structures.

Limited view CT reconstruction and segmentation via constrained metric labeling.

This paper proposes a new discrete optimization framework for tomographic reconstruction and segmentation of CT volumes when only a few projection views are available. The problem has important clinical applications in coronary angiographic imaging. We first show that the limited view reconstruction and segmentation problem can be formulated as a "constrained" version of the metric labeling problem. This lays the groundwork for a linear programming framework that brings metric labeling classification and classical algebraic tomographic reconstruction (ART) together in a unified model. If the imaged volume is known to be comprised of a finite set of attenuation coefficients (a realistic assumption), given a regular limited view reconstruction, we view it as a task of voxels reassignment subject to maximally maintaining consistency with the input reconstruction and the objective of ART simultaneously. The approach can reliably reconstruct (or segment) volumes with several multiple contrast objects. We present evaluations using experiments on cone beam computed tomography.

Brachytherapy seed localization using geometric and linear programming techniques.

We propose an optimization algorithm to solve the brachytherapy seed localization problem in prostate brachytherapy. Our algorithm is based on novel geometric approaches to exploit the special structure of the problem and relies on a number of key observations which help us formulate the optimization problem as a minimization integer program (IP). Our IP model precisely defines the feasibility polyhedron for this problem using a polynomial number of half-spaces; the solution to its corresponding linear program is rounded to yield an integral solution to our task of determining correspondences between seeds in multiple projection images. The algorithm is efficient in theory as well as in practice and performs well on simulation data (approximately 98% accuracy) and real X-ray images (approximately 95% accuracy). We present in detail the underlying ideas and an extensive set of performance evaluations based on our implementation.

Effect of isotonic exercise training on left ventricular volume during upright exercise.

To determine the changes in left ventricular volume and their time course during exercise we studied 30 runners. Left ventricular end-diastolic and end-systolic volumes were measured from biapical two-dimensional echocardiograms recorded during graded upright bicycle exercise. The validity of this echocardiographic technique was assessed by comparing measurements at rest and exercise with results obtained by gated equilibrium radionuclide angiography in 10 patients with coronary artery disease. Although the absolute volume measurements were lower by echocardiography, ejection fraction was not significantly different and the directional changes in volume during exercise were comparable. In the runners, resting left ventricular end-diastolic volume measurements by echocardiography correlated with their maximum bicycle exercise endurance times (r = .80). Left ventricular end-diastolic volume, stroke volume, and ejection fraction increased during exercise with the most marked changes occurring in the first half of exercise. Systolic blood pressure/end-systolic volume (SBP/ESV) also increased during exercise, but the largest change occurred during the second half of exercise. Left ventricular volumes were larger in the 12 competitive marathon runners (maximum exercise duration greater than or equal to 27 min) as compared with the 18 noncompetitive runners (exercise duration less than or equal to 23 min): resting end-diastolic volume 130 +/- 29 (SD) ml vs 87 +/- 20 ml (p less than .001), respectively. During exercise the competitive runners exhibited a larger increase in end-diastolic volume and the noncompetitive athletes showed a greater increase in SBP/ESV. Therefore, highly trained competitive marathon runners make greater use of the less energy-consuming Frank-Starling mechanism to accomplish high levels of isotonic exercise performance as compared with less well-trained runners.

Regional coronary vasoconstriction after combined beta-adrenergic and calcium channel blockade in patients with coronary artery disease.

The beta-adrenergic and calcium channel blocking drugs, which individually and combined have proven efficacious in the treatment of angina pectoris, appear to have opposing effects on coronary artery vasomotion. Previous studies have shown that beta-adrenergic blockade may potentiate and calcium channel blockade reverse coronary vasoconstriction during adrenergic cold stimulation in patients with coronary artery disease. To assess the coronary hemodynamic effects of combined drug therapy, thermodilution coronary sinus and great cardiac vein flow and mean arterial pressure were measured during serial cold pressor testing, both before and after 0.1 mg/kg of intravenous propranolol and again after the addition of 10 mg of sublingual nifedipine in 21 patients (9 without [group A1] and 12 with [group A2] greater than 50% narrowing of the left anterior descending coronary artery). In an additional 15 patients (6 patients without [group B1] and 9 with [group B2] left anterior descending artery stenosis), serial cold pressor testing was performed reversing the drug order. Despite significant increases in mean arterial pressure (p less than 0.01) during cold pressor testing, coronary sinus resistance responses after propranolol plus nifedipine were not statistically significant for any group. However, regional coronary resistance responses differed between patients with and without left anterior descending artery stenosis. In group A1, great cardiac vein resistance was unchanged after propranolol plus nifedipine. In group A2, great cardiac vein flow decreased significantly after propranolol plus nifedipine from 8 +/- 17 to -4 +/- 12% (p less than 0.01 versus control), and great cardiac vein resistance increased from 4 +/- 21 to 15 +/- 19% (p less than 0.01 versus control). A similar significant response was observed for groups B1 and B2. Regional coronary vasoconstriction during adrenergic stimulation after combined drug therapy was only observed in patients with significant left anterior descending artery stenosis. These data suggest that in some patients with severe coronary artery disease, combined beta-adrenergic and calcium channel blockade modified regional coronary responses to adrenergic stimulation with an inhomogeneous distribution of blood flow to potentially ischemic regions without affecting total coronary blood flow. These data also imply that an improvement in anginal symptoms after combined drug therapy may be due primarily to mechanisms that reduce myocardial oxygen demand rather than to improved myocardial oxygen supply.

Long-term efficacy of high-dose diltiazem for chronic stable angina pectoris: 16-month serial studies with placebo controls.

In order to assess the long-term efficacy of diltiazem for the treatment of angina pectoris, eight patients with chronic stable exertional angina who were previously entered into a 4-month randomized, double-blind placebo controlled study, were studied for an additional 12-months. The patients continued to take diltiazem, 360 mg/day, and underwent treadmill exercise testing after 10 and 16 months of therapy. A single-blind placebo week was introduced after 16 months and a treadmill test was performed at the end of this week. Diltiazem therapy continued to augment exercise duration until 0.1 mV of ECG ST depression at 10 and 16 months as compared to the final placebo period: 573 +/- 133 (SD) seconds at 10 months; 565 +/- 148 seconds at 16 months; vs 431 +/- 151 seconds at final placebo (both p less than 0.001). Also, the time to angina pectoris was prolonged on diltiazem by 181 seconds at 16 months (p less than 0.01) and the total duration of exercise was increased by 101 seconds (p less than 0.001) as compared to placebo. In addition, angina frequency decreased from 17 +/- 11 attacks/week on placebo to 0.6 +/- 0.6 attacks/week during diltiazem therapy at 16 months. Two of the eight patients noted mild pedal edema, but no other adverse effects were experienced. Thus diltiazem, 360 mg/day, can be an effective single agent for the long-term treatment of chronic stable angina pectoris.

Attenuation correction of equilibrium radionuclide angiography for noninvasive quantitation of cardiac output and ventricular volumes.

Gated equilibrium radionuclide angiography (RNA) provides count information which is proportional to ventricular volumes. In order to convert ventricular count data directly to accurate absolute volumes, we performed attenuation correction on equilibrium radionuclide angiograms by means of a simple geometric method of attenuation distance quantitation. Attenuation distance defined during imaging agreed with similar measurements obtained during fluoroscopy (r = 0.86). In seven patients, 23 simultaneous cardiac output determinations by Fick and radionuclide imaging techniques showed excellent correlation over a wide range of cardiac outputs (r = 0.91). Radionuclide angiographic ventricular volumes correlated with contrast angiographic ventricular volumes in 28 patients (r = 0.80). The weaker correlation found for ventricular volume data may be due to inaccuracies in ventricular volume calculation when single-plane contrast angiography is applied to patients with wall motion abnormalities. We conclude that attenuation-corrected RNA allows direct calculation of cardiac output and ventricular volumes in individual patients without use of regression equations.

Comparative value of 2-dimensional echocardiography and radionuclide angiography for quantitating changes in left ventricular performance during exercise limited by angina pectoris.

To compare left ventricular (LV) ejection fraction (EF) measurements made during exercise by 2-dimensional echocardiography (2-D echo) and gated equilibrium radionuclide angiography (RNA), 18 patients with angina pectoris were studied during graded upright bicycle ergometry. For RNA, the left anterior oblique view was used with the patient grasping the camera gantry during the 2-minute count acquisition required for EF calculation. For 2-D echo, biapical views were recorded with the patient's arms resting on a platform, and EF was calculated from volume measurements made using Simpson's rule. Exercise duration was similar for both studies, but EF at maximal exertion was higher by RNA than by 2-D echo (46 +/- 15% vs 35 +/- 15%, p less than 0.001). However, echo EF determined 1 minute before maximal exertion, which corresponded to the midpoint of the 2-minute count collection period for RNA, was similar to the RNA value at maximal exercise (44 +/- 12%). Analysis of individual EF values by 2-D echo at rest, at 1 minute before maximal exercise and at maximum exercise showed that there was little change in EF during submaximal exercise, but that EF decreased considerably at maximal exertion when the patients had angina pectoris. Therefore, when the time frame of data acquisition is considered, exercise 2-D echo and gated equilibrium RNA provide similar information regarding LVEF. The latter has the advantage of a 100% successful study frequency and the former is superior in its ability to detect the rapid changes in LV performance during exercise-limiting symptoms.

Short- and long-term efficacy of high-dose oral diltiazem for angina due to coronary artery disease: a placebo-controlled, randomized, double-blind crossover study.

The effects of oral diltiazem (360 mg/day) on exercise tolerance, left ventricular performance, and plasma lactate and catecholamine levels were studied in 13 patients with atherosclerotic coronary artery disease in a placebo-controlled, randomized, double-blind protocol. Exercise duration to the onset of ischemic ST segment depression, time to angina pectoris, and time to peak exercise improved by 120, 174, and 144 sec, respectively (p less than .0001). Left ventricular ejection fraction, as determined by radionuclide angiography, increased in patients at rest from 52 +/- 11% (mean +/- SD) during placebo therapy to 58 +/- 11% during diltiazem therapy (p less than .001); at peak exercise ejection fraction increased from 44 +/- 11% during placebo treatment to 52 +/- 15% during diltiazem therapy (p less than .01). The mean plasma norepinephrine level in patients at rest increased from 498 +/- 221 pg/ml during placebo treatment to 667 +/- 272 pg/ml during diltiazem therapy (p less than .05). Resting standing blood pressure and supine and standing diastolic blood pressures decreased significantly with diltiazem. In all 10 patients followed over a long term, oral diltiazem caused persistent improvement in exercise performance at 12 to 20 weeks, without evidence of placebo effects. Thus, diltiazem is highly effective in divided doses of 360 mg/day for the therapy of chronic angina pectoris due to coronary artery disease.

Angioplasty catheter communication mimicking coronary arterial dissection.

We report a case in which a sudden communication between the pressure and balloon inflation lumens of a percutaneous transluminal angioplasty (PTCA) catheter angiographically mimicked dissection of the coronary artery. This case illustrates a previously undescribed catheter artifact that must be differentiated from other complications of PTCA.

Arizona hinshawii infection of an atherosclerotic abdominal aorta.

A patient with Arizonae hinshawii infection of an atherosclerotic abdominal aortic aneurysm is described to emphasize the similarity of the nonenteric infections of man by Arizona and Salmonella organisms. These genera are similar bacteriologically, ecologically, and clinically. This case emphasizes the need for thoroughly considering the differential diagnosis when encountering cryptic bacteremia with either organism.