Biomedical subjects
Publications and source records attributed to A K George.
We report a neodymium fiber laser incorporating an all-solid photonic bandgap fiber to suppress the four-level laser transition 4F(3/2)-4I(11/2). We demonstrate lasing at 907 nm on the three-level transition 4F(3/2)-4I(9/2) when pumping at 808 nm. The maximum slope efficiency obtained was 32% with a threshold pump power of 70 mW.
We report a new method for making low-loss interfaces between conventional single-mode fibers and photonic crystal fibers (PCFs). Adapted from the fabrication of PCF preforms from stacked tubes and rods, this method avoids the need for splicing and is versatile enough to interface to virtually any type of index-guiding silica PCF. We illustrate the method by forming interfaces to two problematic types of PCF, highly nonlinear and multicore. In particular, we believe this to be the first method capable of individually coupling light into and out of all the cores of a fiber with multiple closely spaced cores, without input or output cross talk.
We describe the design and fabrication of a photonic bandgap fiber formed with two different glasses. As in a hollow-core fiber, light is guided in a low-index core region because of the antiresonances of the high-index strands in the fiber cladding. The structure described represents an ideal bandgap fiber that exhibits no interface modes and guides over the full width of multiple bandgaps.
Abnormalities of left ventricular function are often present in patients with diabetes who are in a stable metabolic state. To determine whether acute metabolic abnormalities may contribute to pathogenesis, patients with diabetes and ketoacidosis (Group 1) or hyperglycemia without ketosis (Group 2) were studied. They were assessed noninvasively for evidence of acute injury or dysfunction of the myocardium. Left ventricular function was assessed on admission and after clinical recovery. Myocardial enzyme release was examined during the acute phase. In Group 1, plasma glucose averaged 32 mM/L and carbon dioxide content 12.4 mEq/L. On echocardiography, the initial circumferential shortening velocity of 1.85 + 0.07 circumferences per second was significantly higher than the final circumferential shortening velocity of 1.31 + 01 (P < 0.005). The systolic time interval ratio, pre-ejection period/left ventricular ejection time, was significantly lower on the initial day compared with the second study. These data are consistent with enhanced ventricular performance. In group 2, plasma glucose averaged 29 mM/L, and carbon dioxide content was normal. The initial circumferential shortening velocity of 1. 1 circumferences per second and pre-ejection period/left ventricular ejection time ratio of 0.38 were normal and remained unchanged. There was no significant alteration of heart rate or arterial pressure in either group. In both groups, total serum lactate dehydrogenase and creatinine phosphokinase levels, as well as their cardiac isoenzymes, were within normal limits. Therefore, the initial increase of myocardial performance and subsequent restoration to normal, as well as the lack of cardiac enzyme increase in plasma, support the view that shortterm ketoacidosis does not contribute to the abnormalities of ventricular function in diabetes.
There has been no study comparing the efficacy of dobutamine and exercise echocardiography in detecting coronary artery disease (CAD) or their physiologic effects at ischemic threshold in the same group of patients. To accomplish this, 52 patients presenting for coronary angiography underwent supine ergometer exercise and dobutamine echocardiography. Compared with angiography, the overall sensitivity of detecting CAD was 78% for exercise and 86% for dobutamine echocardiography (p = NS). The sensitivities of detecting patients with 1-, 2-, 3- and multivessel CAD with exercise echocardiography were 63, 80, 100 and 90%, respectively, and with dobutamine echocardiography 75, 90, 100 and 95%, respectively (p = NS, exercise vs dobutamine). The specificity of both tests was 87%. At ischemic threshold, heart rate was significantly lower with dobutamine than with exercise echocardiography (91 +/- 3 vs 114 +/- 3 beats/min; p < 0.001), systolic blood pressure was significantly lower with dobutamine testing (155 +/- 5 vs 176 +/- 6 mm Hg; p < 0.01), and rate-pressure product was significantly lower with dobutamine stress (14.1 +/- 0.7 vs 19.8 +/- 0.8 x 10(3) beats/min x mm Hg; p < 0.001). It is concluded that the efficacy of detecting CAD by exercise and dobutamine echocardiography is comparable, and the physiology at ischemic threshold of the 2 methods is significantly different and suggests a different means of inducing myocardial ischemia.
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