Experimental myocardial infarction. IV. Reduction of left ventricular compliance in the healing phase

Compliance of the infarcted left ventricle was studied in dogs 3-5 days after occlusion of the left anterior descending coronary artery. Compliance was assessed from postmortem pressure-volume curves and from pressure-length measurements (mercury-in-silastic segment length gauges) made both in vivo and postmortem. Postmortem pressure-volume curves showed reduced compliance compared to sham-operated animals. Postmortem pressure-length curves of infarcted and adjacent normal myocardium indicated that the diminished total compliance could be attributed to an increase in stiffness of the infarcted area. This was confirmed by in vivo end-diastolic pressure-length changes produced by transient aortic occlusion. The infarcted area was akinetic, showing neither contraction nor aneurysmal bulging. In addition, anesthetized dogs with infarcts, when compared with sham-operated animals, had similar left ventricular end-diastolic volumes (indicator dilution method), but higher left ventricular end-diastolic pressures. Taken with previous observations, which show that systolic aneurysmal bulging is uniformly present at the onset of ischemia, these results indicate that stiffening of the ischemic myocardium occurs during the first 5 days after infarction, and show that elevation of left ventricular filling pressure does not necessarily signify ventricular dilatation. The results also suggest a mechanism whereby ventricular performance may improve during recovery from acute myocardial infarction.

Effects of fear on exploratory behaviour in rats

It has been suggested that mild fear may evoke rather than inhibit exploratory responses in rats. The relationship between conditioned fear and exploratory behaviour was analysed in three experiments and there was no evidence that mild fear increased exploration. Conditioned fear was found to be under relatively precise stimulus control and its magnitude was related to the intensities and durations of the unconditioned stimulus, inescapable electric shock.

Hemodynamic effects of pneumonia. II. Expansion of plasma volume

Previous work has demonstrated that approximately one-third of patients with pneumonia have a hypodynamic circulatory response. This response is characterized by an abnormally wide arteriovenous oxygen difference, a low cardiac output, increased peripheral resistance, and an increased hematocrit. This state was found to abate in convalescence. In an attempt to elucidate the pathogenesis of this hypodynamic state, nine additional patients were studied hemodynamically during the acute phase of pneumonia before and during acute expansion of blood volume by low molecular weight dextran (seven patients) or normal saline (two patients). Five patients were restudied before and during acute blood volume expansion in convalescence. Three patients with pneumonia had a normal arteriovenous oxygen difference (< 5.5 vol%), and six patients were hypodynamic in that their arteriovenous oxygen differences were greater than 5.5 vol%. With expansion of blood volume in the acute phase of pneumonia, all patients showed an increase in cardiac output, a decrease in arteriovenous oxygen difference, and a decrease in peripheral vascular resistance; however, the percentage change in the hypodynamic patients was not as great as occurred in the patients with normal hemodynamics nor as great as occurred when restudied in convalescence. Likewise, all patients had a normal or near normal hemodynamic profile in convalescence. In addition, ventricular function in the acute phase of pneumonia was depressed. The findings suggest that the hypodynamic state associated with acute pneumonia is due to depressed myocardial contractility to which relative hypovolemia may contribute.

Experimental myocardial infarction. II. Acute depression and subsequent recovery of left ventricular function: serial measurements in intact conscious dogs

Acute myocardial infarction causes depression of left ventricular function, but the capacity of the ventricle to recover from such an injury remains unknown. This problem was explored by measuring left ventricular function in eight intact conscious dogs before, 1 hr after, and again 6-8 days after myocardial infarction. Acute myocardial infarction was produced using a technique which entails gradual inflation over an average period of 1 hr of a balloon cuff previously implanted around the left anterior descending coronary artery. Occurrence of anterior wall infarction was detected electrocardiographically and later confirmed by postmortem examination. Left ventricular function was evaluated from the relationship between left ventricular developed pressure (left ventricular peak systolic pressure minus left ventricular end-diastolic pressure) and left ventricular end-diastolic pressure during transient aortic occlusion with a balloon catheter. Left ventricular function curves were obtained by plotting left ventricular-developed pressure at increasing left ventricular end-diastolic pressures up to 50 mm Hg. Acute myocardial infarction caused marked depression of left ventricular function measured 1 hr after onset of infarction, but 1 wk later all eight animals showed improvement with return of function toward the control levels. A small but significant descending limb was noted at left ventricular end-diastolic pressures above 35 mm Hg. Quantitatively, the descending limb was similar before, 1 hr after, and 1 wk after myocardial infarction. Hemodynamic data revealed evidence of left ventricular failure in all animals, but variability in individual hemodynamic parameters was noted. The data indicate that the marked depression of left ventricular function observed immediately after experimental acute myocardial infarction undergoes considerable resolution within 1 wk, but that functional recovery remains incomplete.

The Fluorinated Quinolones

Abstract:

Following the discovery of nalidixic acid in 1962, numerous structural modifications have been made to the quinolone nucleus to increase antimicrobial activit> and improve pharmacokinetic performance. A major advance occured during the 1980\ with the discovery that a fluorine at position-6 conferred broad and potent antimicrobial activity, (e.g. norfloxacin) but still with relatively less activity for Gram-positive and antiaerobic organisms than Gram-negative bacteria. Subsequent developments produced quinolones with further improvements, predominantly in either solubility (e.g. ofloxacin), antimicrobial activity (e.g. ciprotloxacin) or prolonged serum half-life (e.g. pefloxacin). Recent modifications have attempted to achieve an optimal blend of favourable prupcn1c, together with minimal potential for undesirable side-effects. The mode of action of quinolones is by blocking of the bacterial enzyme gyrase. This enzyme is responsible for the coiling and supercoiling of the DNA within the cell. When this enzyme is inhibited, DNA transcription, which results in protein synthesis, and DNA replication, which results in cell division, are inhibited. Improvements in antimicrobial activity combined with adequate blood and tissue concentrations do offer expectancy of enhanced therapeutic efficacy for new derivatives in those infections by organisms which are 'marginally' sensitive to currently used quinolones. The possibility of resistance emerging in these organisms during treatment should also be reduced.

Experimental Trypanosoma cruzi myocarditis: relative effects upon the right and left ventricles

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Morphology and relationships of the Pentatomoidea (Heteroptera)

Evidence from the morphology of the alimentary organs, genitalia, immature stages, and biology is described to support a subfamily status for Oncomerinae in the Tessaratomidae. It has been shown that the Oncomerinae is a homogeneous group and its division into subgroups is unwarranted. The developmental stages of seven species of native Australasian oncomerines are described and a scheme of the higher classification of the Tessaratomidae is presented.