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D Sack

Publications and source records attributed to D Sack.

36 records · Page 2Linked to original sources
PubMed1989

Global myocardial hypertrophy in conscious dogs with chronic elevation of plasma norepinephrine levels.

Chronically elevated plasma norepinephrine is associated with many disease states in which myocardial hypertrophy is also found, yet whether the hypertrophy results from the hemodynamic actions of catecholamines or a trophic effect is still unknown. The goal of our study was to determine the extent of hypertrophy following 28 days of norepinephrine infusion and the role of altered hemodynamics as the stimulus for the hypertrophy in conscious dogs. In a retrospective study gross cardiac weights were examined in 25 control instrumented dogs (controls) and in 41 instrumented dogs with elevated norepinephrine (NE). In the NE dogs LV (94 +/- 2.8 g), septum (33 +/- 1.5 g) and total heart weights (172 +/- 4.5 g) were greater than in controls (85 +/- 5.0, 31 +/- 1.9, and 158 +/- 9.0 g, respectively). The LV (3.95 +/- 0.10 g/kg), RV (1.91 +/- 0.06), septum (1.38 +/- 0.06) and total weight (7.23 +/- 0.15) to body weight ratios were also significantly greater (3.32 +/- 0.12, 1.73 +/- 0.08, 1.24 +/- 0.06, and 6.28 +/- 0.23 g/kg). The dry/wet weight ratios were not different in the two groups. After cutting the hearts into 1 cm rings, the planimetered area of each ring showed that the wall thickness increased at all levels, e.g. at the base by 25 +/- 3.2%. The chamber internal diameter was significantly increased only near the apex in the NE dogs making the heart more cylindrical in shape. There was no obvious sign of fibrosis in any layer of the myocardium. In physiologic studies, no index of contractility was altered including: LV dP/dt, LV dD/dt, shortening, LV dWT/dt and there was also no change in preload. Heart rate was significantly reduced throughout the 28 days of study. Cardiac output was reduced and there were no significant changes in cardiac work. Thus in these dogs NE caused a 19% and 10% increase in LV and RV to body weight ratios, respectively, without any obvious hemodynamic stimulus.

Animals↗
PubMed1987

Absence of hypertension despite chronic marked elevations in plasma norepinephrine in conscious dogs.

To better define the mechanisms of blood pressure control in states of catecholamine excess, we infused norepinephrine for 28 days using subcutaneously implanted osmotic pumps in dogs previously instrumented for monitoring left ventricular dynamics and cardiac output. Plasma norepinephrine rose from 238 +/- 27 to 4346 +/- 952 pg/ml at 21 days, while epinephrine and dopamine levels did not change. Heart rate fell from 85 +/- 4 to 63 +/- 6 beats/min, while arterial pressure was unchanged from baseline. Total peripheral resistance rose 0.011 +/- 0.003 mm Hg/ml/min from a control value of 0.029 +/- 0.002 mm Hg/ml/min, and cardiac output decreased 1093 +/- 292 ml/min from a baseline level of 3575 +/- 156 ml/min. Since stroke volume did not change, the maintenance of arterial pressure is related to decreases in cardiac output secondary to bradycardia. Buffering mechanisms are responsible for maintenance of systemic arterial pressure because hexamethonium and atropine caused hypertension. Although left ventricular end-diastolic pressure, end-diastolic diameter, shortening, rate of change of pressure, velocity of myocardial shortening, cardiac work, stroke work, and the double product did not change significantly during the study, postmortem examination demonstrated biventricular hypertrophy. Thus, despite markedly elevated catecholamine levels and no elevation of systemic arterial pressure, myocardial hypertrophy developed. These studies lend support to the hypothesis that norepinephrine may be a direct myocardial tropic hormone and suggest that intense activation of reflex buffering mechanisms maintains blood pressure in the normal range during chronic catecholamine infusion.

Animals↗
PubMed1987

AIDS in the workplace.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗
PubMed1983

Genetic transfer of antimicrobial resistance and enterotoxigenicity among Escherichia coli strains.

To understand the role of enterotoxin (Ent) plasmids in epidemics of enterotoxigenic (ET) Escherichia coli diarrhea in the United States, we studied the genetics of Ent plasmids in relation to E. coli serotypes and R plasmids. Twenty-nine ET E. coli strains, including all epidemic isolates available at the Centers for Disease Control, Atlanta, Ga. (CDC), were assessed for the ability to transfer antimicrobial resistances (if present) by conjugation, to mobilize a nonconjugative R plasmid, and to cotransfer enterotoxigenicity with R determinants. Of the 12 ET E. coli strains isolated in the United States, 5 were able to transfer R plasmids; one strain cotransferred detectable enterotoxigenicity. Another four U.S. isolates were able to mobilize plasmid DNA, but no toxin production was detected in transconjugants. Of 17 resistant ET E. coli from South Asia, 13 were able to transfer R plasmids; 5 of those 13 cotransferred detectable Ent plasmids. In all, 22 ET E. coli strains (76%) were able to initiate conjugation and genetic transfers. Six of these strains (20%) were able to cotransfer enterotoxigenicity with a conjugative R plasmid at a detectable frequency. One of the six strains transferred R and Ent determinants on a single plasmid. These data are addressed in relation to the observed immobility of Ent and R during outbreaks of ET E. coli, the efficacy of prophylactic tetracycline, and the worldwide occurrence of a limited number of ET E. coli serotypes.

Conjugation, Genetic↗
PubMed1983

Circadian rhythm disturbances in manic-depressive illness.

Clinical features of manic-depressive illness, such as diurnal variation in mood, early morning awakening, and cyclicity and seasonality of recurrences, have led to speculation that the circadian system may be involved in its pathophysiology. At least three types of circadian rhythm abnormalities have been described in such patients: blunting of circadian rhythms' amplitudes, advanced position (or even nonentrainment) of circadian rhythms' phases, and doubling of the length of the sleep-wake cycle from 24 to 48 h. Several types of experiments indicate that alterations in the timing of sleep and wakefulness relative to other circadian rhythms (i.e., changes in internal phase relationships) may trigger the onset or offset of episodes of depression and mania. Whether drugs used to treat manic-depressive illness act through their effects on the circadian system is currently being investigated. Direct manipulations of the circadian system are also being investigated as new approaches to treatment.

Bipolar Disorder↗
PubMed1978

[Treatment of acute myocardial infarction with metoprolol (author's transl)].

Metoprolol, a cardioselective beta-receptor blocker, was administered to 12 patients three to ten hours after sustaining a transmural myocardial infarction, and the effect of the drug (10 mg i.v., followed by 50 mg orally every eight hours) was followed for 48 hours. Heart rate decreased by 16% and cardiac output by 27%, while blood pressure and stroke volume decreased little and pulmonary "wedge" pressure was not significantly changed. Even in patients with initially definitely elevated left-ventricular filling pressure (greater than 20 mm Hg) the drug was well tolerated without any further rise in pressure. Since left-ventricular work was significantly decreased (stroke work--15%, cardiac output--31%) and the duration of diastole, decisive for coronary perfusion, was prolonged, it is concluded that early administration of beta-receptor blockers has a favourable effect on myocardial oxygenation and possibly reduce ultimate infarct size.

Acute Disease↗
PubMed1977

[Treatment of acute myocardial infarction with sodium nitroprusside (author's transl)].

In 12 patients with acute myocardial infarction, seven of whom had high and five low blood pressure measurements, sodium nitroprusside infusions were given to reduce the myocardial oxygen consumption. The dosage was between 20 and 300 mug/min. Sodium nitroprusside led to a considerable reduction of the systemic arterial pressure, while the left ventricular filling pressure was less influenced. In normotensive patients the filling pressure could often not be sufficiently lowered as a too severe reduction of arterial pressure occurred beforehand. In hypertensive patients the relationship between left ventricular filling pressure and arterial pressure was better: in all patients the arterial pressure could be lowered to normal values and the filling pressure also became normal in most cases. Angina pectoris improved markedly in all patients. These results show that sodium nitroprusside has a satisfactory effect on the haemodynamics in hypertensive infarct patients, whereas it is less suitable for the treatment of normo- or hypotensive patients.

Acute Disease↗
PubMed1977

[Nitroprusside-sodium and intravenous nitroglycerin in acute myocardial infarction (author's transl)].

Using Nitroglycerin (NTG) and Nitroprusside-Sodium (NPN) intravenously we tried to reduce the necrotic area following myocardial infarction by reducing the myocardial O2 consumption. In 12 patients with acute myocardial infarction the effect of NPN was compared to intravenous NTG. In all patients the blood pressure, the pulmonary artery pressure, the pulmonary capillary wedge pressure and the heart rate were continuously monitored; in few patients with cardiac output was measured using a thermodilution device. In some patients with normal blood pressure NPN lowered the blood pressure to such a degree that NPN had to be discontinued before and effect on the pulmonary capillary wedge pressure could be seen. Even in patients with normal blood pressure this effect was not seen with NTG. Intravenous NTG lowered the pulmonary capillary wedge pressure in most patients with only a moderate effect on the blood pressure. We conclude from our results that patients with acute myocardial infarction and normal blood pressure should receive NTG, if a lowering of the pulmonary capillary wedge pressure is desired. When NPN was used in this group of patients a considerable decline of the blood pressure was seen. We think that an elevated pulmonary capillary wedge pressure should be treated with NPN only in patients with an elevated blood pressure.

Acute Disease↗
PubMed1976

Experimental myocardial infarction in the cat. I. Reversible decline in contractility of noninfarcted muscle.

The contractile state of the noninfarcted myocardium was examined in adult cats after myocardial infarction produced by ligation of several branches of the left coronary artery. At 2 days, 7 days, and 6 weeks after infarction, and after determination of intracardiac pressures, papillary muscles were exicised from the noninfarcted segment of the right ventricle and attached to a myograph for analysis of contractile function. One week after infarction there was a decline in actively developed force at Lmax, caused by a decrease in the rate of force development. In addition, the response to procedures that augment myocardial contractility, such as paired stimulation and increasing the frequency of electrical stimulation, was significantly depressed. Two days after infarction, changes were less significant, although similar in direction. Six weeks after infarction, developed force at Lmax had returned to normal values. The response to procedures augmenting contractility also had returned to normal. There appears to be a distinct, reversible loss of contractility in the remaining viable myocardium in the early phase after experimental infarction.

Animals↗
PubMedDate not supplied

Increased productivity of a digital imaging system: one hospital's experience.

During peak hours of operation, it was not uncommon for the radiology department at St. Luke's Episcopal Hospital in Houston, Texas, to have a backlog of six to ten patients. While some of this was due to competing schedules from the emergency department (ED) and inpatients, the major problem was an inefficient workflow, especially for emergency department patients. Our staff in the radiology department worked with the hospital management to include plans for a new radiology room in an ED renovation project. In designing the new radiology room the most important issues under consideration were the physical location of the room and the type of radiography system to be installed. With plans to implement PACS, we evaluated computed radiography and digital radiography options. At St. Luke's, we had had our first experience with digital radiography after the purchase of a dedicated digital chest system. As a beta test site for the manufacturer, we had an opportunity to test--what was at the time--a new digital radiography system. The powerful impact of digital radiography became most evident by the decreased patient backlog. Even without PACS, workflow became dramatically more efficient. Images now are available for review within seconds after exposure, since there are no films to process. This has reduced our average exam time from ten minutes to one and a half minutes, not including patient transport time. The efficiency demonstrated with the digital chest system provided evidence that digital systems could handle significantly more patients than computed radiography or screen-film systems, without a compromise in image quality. Therefore, we decided to put a digital radiography system in the new ED radiology room. We estimate that the new unit will pay for itself in less than three years.

Efficiency, Organizational↗