Load dependence of isovolumic relaxation in intact heart: facts or artifacts?

In order to study the dependence of left ventricular isovolumic relaxation on preload, afterload, and contractility the effects of infusions of dextran, phenylephrine, and dobutamine were assessed in 10 closed chest anaesthetised dogs. Left ventricular and aortic pressures and left ventricular transverse diameters were measured by micromanometers and a tracking sonomicrometer. Isovolumic relaxation time constant was computed by two different single exponential models: the first (time constant Tw) assumed the horizontal asymptote as equal to zero, whereas the second (time constant Tl) assumed a variable asymptote (Pb). To compare the two models, deviations between observed and predicted left ventricular pressures during isovolumic relaxation were computed for both (average squared difference ARSSQw and ARSSQl respectively). Dextran infusion, although increasing preload indexes, did not affect Tl (from 35.1(2.6) to 38.5(2.2) ms, NS) (mean(SEM], but increased Tw (from 28.4(1.4) to 43.8(2.1) ms, p less than 0.001); Pb was significantly shifted upwards (from -7.9(2.4) to +8.2(2.8) mmHg, p less than 0.01). Pb correlated with left ventricular end diastolic pressure (r = 0.71, p less than 0.001). Phenylephrine infusion did not change the isovolumic relaxation time course (Tl from 36.4(3.5) to 46.2(6.1) ms, NS; Tw from 26.8(2.3) to 30.5(2.9) ms, NS) nor Pb (from -9.5(2.3) to -18.7(2.3) mmHg, NS). Dobutamine infusion reduced Tl significantly (from 35.2(3.7) to 25.3(2) ms, p less than 0.02), but did not change Tw (from 27.5(2.4) to 23.3(3.3) ms, NS) nor Pb (from -7.3(1.8) to -8.8(2.3) mmHg, NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute haemodynamic effects of ibopamine and dopamine on isovolumic relaxation.

The effects of intraduodenal ibopamine (a new orally active inotropic agent claimed to have haemodynamic effects similar to dopamine) on isovolumic relaxation were monitored for 90 min in eight closed-chest anaesthetized dogs. Dopamine and epinine (ibopamine active metabolite) were also infused at graded doses. After 15 min, ibopamine (12 mg/kg) shortened the time constant of isovolumic relaxation, and increased stroke volume and mean aortic pressure. Peak positive dP/dt increased significantly only 10 min later. Heart rate did not change. Dopamine (10 micrograms/kg per min) similarly reduced the time constant, and increased stroke volume, mean aortic pressure, peak positive dP/dt and heart rate. Epinine (10 micrograms/kg per min) caused similar changes in peak positive dP/dt, stroke volume, mean aortic pressure, and accelerated time constant without raising the heart rate. Ibopamine and epinine therefore significantly improved the isovolumic relaxation phase, like dopamine, without however affecting the heart rate.

Microcomputer-aided diagnosis in cardiology. An expert system based on clinical and phono-mechanocardiographic data.

A knowledge-based consultation system capable of making multiple diagnoses in noninvasive cardiology is presented here. The system, expressly designed for a personal computer, is able to provide assistance in the diagnosis of 49 disease-entities. When tested in 52 retrospective cases (33 patients with one disease-entity, 17 with two, 2 with three), it made 39 correct diagnoses (75%). The average score of the actually present disease-entities was 94 +/- 3.2 (mean +/- standard error of the mean), significantly higher than the highest score obtained by the incorrect diagnoses (87.2 +/- 3.1) (p less than 0.001). The system was able to correctly perform 1 triple diagnosis and 9 double diagnoses. The results obtained, comparable with those of well-known expert systems (MYCIN, INTERNIST-1), demonstrate the reliability of a microcomputer-based expert system for medical diagnosis in cardiology.

Silent ischaemia in post-myocardial infarction patients submitted to physical training.

Recently, more attention has been focused on the detection and treatment of silent myocardial ischaemia. Electrocardiographic signs of exercise-induced asymptomatic myocardial ischaemia are very common findings among survivors of acute myocardial infarction. From data of our population we found that silent exercise-induced ischaemia is present in 15-20% of all patients, and that about half of the patients with exercise-induced ST-segment depression were free of symptoms. Ergometric data at the ischaemic threshold are similar between asymptomatic and symptomatic patients while the presence of symptoms is more frequent in patients who were also symptomatic before the myocardial infarction. During the training period, the majority of the 'silent' patients remained asymptomatic, 23% developed effort angina, and 9% developed angina at rest. Training monitoring may be helpful in identifying the variability of symptoms. Physical training, in particular an intermittent programme, increased the work-load at which the ECG ischaemic signs appeared. Among the possible mechanisms responsible for exercise-induced silent ischaemia, a different pain tolerance and control of analgesia may be ascribed to explain the absence of pain, perhaps also determined by different endogenous beta-endorphin levels.