Diffraction analysis of decorated Fibonacci chains in the average unit-cell approach.

A novel approach to diffraction analysis of decorated quasicrystals is discussed. An average unit cell has been constructed for a decorated Fibonacci chain and used for analysis of its diffraction pattern. After some transformation of the scattering vectors, all the diffraction peaks are described by a single envelope function which is characteristic of a given decoration. It has been shown that by knowing several diffraction intensities, in a limited range of the scattering vector, it is possible to reconstruct the envelope function successfully and distinguish between different decorated structures.

Volumetric responses of right and left ventricles during upright exercise in normal subjects.

We evaluated the volumetric responses of the right and left ventricles to upright exercise using two noninvasive methods, first-pass radionuclide angiocardiography and the CO2 rebreathing technique, in nine normal subjects. Right (RV) and left (LV) ventricular ejection fractions, heart rate, and cardiac index were determined at rest and during steady-state exercise on the bicycle ergometer at 50% of maximal O2 consumption. From these data, stroke volume index (SVI), end-diastolic volume index (EDVI), and end-systolic volume index (ESVI) were derived. SVI increased from 40 +/- 7 ml/m2 at rest to 59 +/- 13 ml/m2 with exercise (P less than 0.001). RVEDVI increased significantly from 82 +/- 16 ml/m2 at rest to 95 +/- 21 ml/m2 during exercise (P = 0.008), while there was no significant change in RVESVI with exercise. Changes in LVEDVI and LVESVI during upright exercise were similar to the right ventricle. The increase in systolic blood pressure during exercise, along with no change in LVESVI, indicated enhanced ventricular contractility. The normal augmentation in SVI during submaximal exercise was due to both the Frank-Starling mechanism and an increased contractile state. Application of these or similar techniques may be useful in evaluating ventricular performance in patients with cardiorespiratory dysfunction.

Gold-195m for serial first pass radionuclide angiocardiography during upright exercise in patients with coronary artery disease.

Sequential first pass radionuclide angiocardiography can be performed in rapid succession using gold-195m because of its low radiation dose and short half-life (30.5 seconds). In 25 patients with known or suspected coronary artery disease, first pass studies with gold-195m were obtained using a computerized multicrystal gamma camera at rest (n = 29), at the end of each 3 minute stage of exercise (n = 25) and immediately after exercise (n = 23). In 13 patients, assessment of left ventricular function during exercise with gold-195m was combined with thallium-201 stress scintigraphy. Left ventricular ejection fraction at rest assessed with technetium-99m and gold-195m correlated well (r = 0.93). In addition, repeat left ventricular ejection fractions at rest with gold-195m correlated closely (r = 0.96). Comparing peak exercise left ventricular ejection fraction with ejection fraction at rest, abnormal left ventricular reserve was found in 20 of 25 patients. Various abnormal patterns of left ventricular ejection fraction response were noted, showing the diagnostic potential of serial exercise angiocardiography. Thallium-201 myocardial images, obtained on a single crystal gamma camera after multiple gold-195m injections, were all of good diagnostic quality and were abnormal in 10 of 13 patients. Thus, multiple high count rate first pass studies can be obtained with gold-195m during and after exercise, allowing serial study of physiologic changes in left ventricular function during exercise. Thallium-201 myocardial imaging can be performed using the same exercise test, providing direct comparison of myocardial function and perfusion.

Contrasting acute effects of vasodilators (nitroglycerin, nitroprusside, and hydralazine) on right ventricular performance in patients with chronic obstructive pulmonary disease and pulmonary hypertension: a combined radionuclide-hemodynamic study.

Fourteen patients with chronic obstructive pulmonary disease, mild to moderate pulmonary hypertension, and diminished right ventricular (RV) ejection fraction were studied acutely with use of a combined radionuclide-hemodynamic approach to assess and contrast the effects of 3 vasodilators on RV performance and central hemodynamic function. Nitroglycerin significantly decreased mean right atrial pressure, RV end-diastolic volume index, mean pulmonary artery pressure, cardiac index, and arterial oxygen tension, but did not affect pulmonary vascular resistance index and increased RV ejection fraction. Nitroprusside had similar effects on mean right atrial pressure, RV end-diastolic volume index, mean pulmonary artery pressure, cardiac index, and arterial oxygen tension, but also mildly decreased pulmonary vascular resistance index and did not alter RV ejection fraction. In contrast, hydralazine decreased pulmonary vascular resistance index and increased cardiac index and RV ejection fraction. The increase in ejection fraction correlated well with the decrease in pulmonary vascular resistance. These data suggest that in patients with mild to moderate secondary pulmonary hypertension, acute administration of hydralazine results in a substantial improvement in RV performance by virtue of decreasing pulmonary vascular resistance. In contrast, nitroglycerin and nitroprusside demonstrate predominant effects that reduce preload, cardiac index, and arterial oxygen tension. Based on these data, afterload reduction with vasodilators such as hydralazine may be potentially useful in selected patients with pulmonary disease and secondary pulmonary hypertension and appear preferable to agents that primarily reduce preload. Further long-term studies are necessary to establish therapeutic efficacy.

First-pass radionuclide assessment of right and left ventricular performance in patients with cardiac and pulmonary disease.

First-pass radionuclide angiocardiography allows noninvasive determination of right and left ventricular performance from a single study. Analysis is made from the high frequency components of the regional radionuclide time-activity curves. Both regional and global ventricular performance can be assessed at rest and during exercise. Sequential studies can be performed to evaluate therapeutic interventions. This technique has been applied in a broad spectrum of patients with cardiac and pulmonary disease and has been shown to have major clinical impact.