Observation of Quasichanneling Oscillations.

We report on the first experimental observations of quasichanneling oscillations, recently seen in simulations and described theoretically. Although above-barrier particles penetrating a single crystal are generally seen as behaving almost as in an amorphous substance, distinct oscillation peaks nevertheless appear for particles in that category. The quasichanneling oscillations were observed at SLAC National Accelerator Laboratory by aiming 20.35 GeV positrons and electrons at a thin silicon crystal bent to a radius of R=0.15 m, exploiting the quasimosaic effect. For electrons, two relatively faint quasichanneling peaks were observed, while for positrons, seven quasichanneling peaks were clearly identified.

Observation of deflection of a beam of multi-GeV electrons by a thin crystal.

We report on an experiment performing channeling and volume reflection of a high-energy electron beam using a quasimosaic, bent silicon (111) crystal at the End Station A Test Beam at SLAC. The experiment uses beams of 3.35 and 6.3 GeV. In the channeling orientation, deflections of the beam of 400 µrad for both energies with about 22% efficiency are observed, while in the volume-reflection orientation, deflection of the beam by 120 µrad at 3.35 GeV and by 80 µrad at 6.3 GeV is observed with 86%-95% efficiency. Quantitative measurements of the channeling efficiency, surface transmission, and dechanneling length are taken. These are the first quantitative measurements of channeling and volume reflection using a primary beam of multi-GeV electrons.

Cardiac myxoma: the Indiana Heart Institute experience.

Surgical resection of a cardiac myxoma was performed in 14 patients at the Indiana Heart Institute at St. Vincent Hospital and Health Care Center in Indianapolis from 1974 to 1989. Thirteen were located in the left atrium and one in the right atrium. The 10 women and four men ranged in ages from 28 to 75 years. Surgical complications included one perioperative death, one late death and one late recurrence requiring reoperation. Physicians must be highly suspicious to correctly diagnose this unusual but surgically correctable entity. Two-dimensional echocardiography is the diagnostic technique of choice for both early diagnosis of a cardiac myxoma and late follow-up after resection.

Emergency percutaneous transluminal coronary angioplasty in acute myocardial infarction: a 3 year experience.

In 151 patients experiencing acute myocardial infarction, emergency coronary angioplasty was performed as primary therapy. Overall, angioplasty was successful in 132 patients (87%); it was successful in 91 (85%) of 107 patients with a totally occluded infarct-related artery and in 41 (93%) of 44 patients with a subtotally occluded infarct-related artery. After successful angioplasty, mean residual stenosis was 29% (range 0 to 70). Eighteen patients were in cardiogenic shock (12%) including four patients receiving cardiopulmonary resuscitation during the angioplasty procedure. Hospital mortality was 9%, with 7 of 13 deaths occurring in patients presenting with cardiogenic shock or intractable ventricular arrhythmia. Hospital mortality was 5% in patients with successful angioplasty versus 37% in those with unsuccessful angioplasty (p less than 0.001). In the immediate period after angioplasty, left ventricular ejection fraction was significantly lower for patients with lesions of the left anterior descending artery (34 +/- 10%) than for patients with lesions of the left circumflex or right coronary artery (43 +/- 11%). In patients with successful angioplasty, significant improvement in left ventricular ejection fraction averaged 13 +/- 12% (p less than 0.001) for those with lesions of the left anterior descending artery and 10 +/- 12% (p less than 0.001) for those with lesions of the left circumflex or right coronary artery. Repeat coronary angiography was performed in 85 (70%) of 121 patients who had successful angioplasty and survived hospitalization without requiring bypass surgery; restenosis was found in 26 (31%), and angioplasty was repeated in 22 patients, successfully in each.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise testing and training of the elderly patient.

As an invariable accompaniment of the aging process, cardiac function declines, that is, cardiac output, stroke volume, heart rate, and maximum oxygen consumption all decrease. The vital capacity declines as residual volume increases, and ventilation-perfusion imbalance increases. Muscles atrophy and weaken, joints stiffen, and bones are demineralized. Certainly the aging process per se explains a portion of this functional deterioration. Disease states also account for some deterioration. However, inasmuch as approximately one half of the deterioration in function can be prevented or reversed by an exercise training program, it would seem that disuse or inactivity is responsible for at least a portion of the functional decline characteristic of aging. Special considerations in prescribing exercise training for the elderly include careful cardiovascular assessment; evaluation of orthopedic problems; consideration of heat intolerance; and careful attention to motivation. The exercise prescription should be specific and tailored to the subject's individual cardiovascular status, musculoskeletal limitations, and personal goals. Walking, stretching calisthenics, and other aerobic activities, if of reasonable intensity and duration, and when preceded and followed by an appropriate warm-up and cool-down period, respectively, can result in a substantial, positive training effect in the elderly. In response to such a training program, elderly subjects demonstrate an increase in stroke volume, cardiac output, and maximum heart rate. Respiratory function changes little, yet maximal oxygen consumption is increased. Fat may be replaced by lean muscle mass as muscle strength and endurance improve. Flexibility is improved and bone demineralization retarded or even reversed. Exercise has a tranquilizing effect on elderly subjects so that anxiety and depression may be prevented. The subject develops self-respect as effort tolerance improves. An excessively conservative attitude on the part of physicians, families, and elderly subjects has resulted in inappropriate activity limitations with a consequent decrement in effort tolerance. Elderly individuals can maintain a reasonable level of effort tolerance or can be rehabilitated to this level of activity with an appropriate exercise program. The decline in overall function expected with age can be substantially retarded. Consequently, physicians, families, and the subjects themselves should consider the potential advantages of an exercise program.

Randomized withdrawal from nifedipine: placebo-controlled study in patients with coronary artery spasm.

A multicenter randomized double-blind withdrawal study was conducted to compare the efficacy of nifedipine to that of placebo in vasospastic angina. Following a 2-week single-blind nifedipine baseline period, during which nifedipine was maintained at prestudy levels, 38 patients, 19 taking placebo and 19 continuing nifedipine therapy, either completed a 4-week randomized phase or were prematurely withdrawn because of therapeutic failure. During the randomized phase, an increase in median anginal frequency (2.8 attacks/wk, p less than 0.003) and nitroglycerin usage (0.5 tablets/wk, p less than 0.03) occurred only in the placebo group. The randomized phase was prematurely terminated because of anginal exacerbation in 7 of 19 placebo patients (37%) (only 1 patient receiving nifedipine [p = 0.02] experienced anginal exacerbation). Double-blind therapy was judged effective in 16 patients (84%) receiving nifedipine and in 3 patients (16%) receiving placebo (p less than 0.001). Nifedipine was well tolerated. This study establishes the efficacy of nifedipine in the treatment of variant and validates previous clinical experience.

Reversal of digitalis-induced mesenteric vasospasm by sodium nitroprusside.

Digitalis constricts the peripheral vasculature. When digitalis is administered to patients whose mesenteric blood flow is reduced secondary to heart failure, the vasoconstrictor action coupled to reduced mesenteric flow may result in mesenteric ischemia or hemorrhagic bowel necrosis. The clinical syndrome of mesenteric ischemia secondary to heart failure and excess digitalis developed in a patient. Splanchnic vasoconstriction was proved angiographically. Both the vasospasm and clinical evidence of mesenteric ischemia were promptly reversed by sodium nitroprusside.