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Biomedical subjects

H D Schmidt

Publications and source records attributed to H D Schmidt.

115 records · Page 7Linked to original sources
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Quantitative data on the afterload dependence of left ventricular dp/dtmax in isolated canine hearts.

In 15 canine heart-lung preparations the effect of an increase in aortic pressure on left ventricular dP/dtmax was tested. Abrupt elevation of aortic pressure by 20-80 mm Hg during diastole without change in enddiastolic pressure did not influence left ventricular dP/dtmax in the following heart beat. Left ventricular circumference increased slightly. Stepwise elevation of aortic pressure from 60 to 130 mm Hg (LVEDP maintained constant) resulted in an augmentation of the steady-state values of dP/dtmax by only 42 mmHg/s per 10 mmHg pressure rise. If the enddiastolic pressure was not maintained constant, the increase in dP/dtmax was 77 mm Hg/s per 10 mm Hg pressure rise. Aortic pressure alterations exhibit a slight but significant influence on left ventricular contractility in the steady-state phase, while an acute effect is not detectable, thus demonstrating that a sudden increase in coronary perfusion pressure is without immediate effect on the cardiac performance.

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Maximal rate of pressure rise and time parameters in the right ventricle under isovolumic conditions. Investigations in the canine heart-lung preparation.

In contrast to the left ventricle, the maximal rate of intraventricular pressure rise in the right ventricle does not occur within the isovolumic phase of the contraction. Occlusion of the pulmonary artery by inflation of a balloon during the diastole causes an isovolumic systole of the following heart beat. The canine heart-lung preparation was used to test whether dP/dtmax measured isovolumically and the peak ventricular pressure Pmax as well as the parameters derived are useful indices for the contractile state of the right ventricle. Changes only of the aortic pressure influence neither dP/dtmax, Pmax and the time values from the onset of contraction to dP/dtmax (t-dP/dtmax), nor the time to Pmax (t-Pmax). A rise in heart frequency leads to an increase in dP/dtmax and Pmax at lowered enddiastolic pressure. It does not influence the time interval t-dP/dtmax and t-Pmax. With augmented diastolic filling, dP/dtmax as well as Pmax increase, and t-dP/dtmax and t-Pmax are extended. The present study suggests that dP/dtmax and Pmax measured isovolumically provide accurate and practical measurements of right ventricular contractility, provided that changes in enddiastolic pressure and heart frequency are taken into account. The time parameters are found to be not useful.

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The maximal rate of pressure rise in the right ventricle of isolated canine hearts in isovolumic and auxotonic systole under various hemodynamic and inotropic conditions.

The influence of changes in pre- and afterload, heart frequency and inotropic state on the difference between right ventricular dP/dtmax measured isovolumically and auxotonically has been investigated in canine heart-lung preparations. Isovolumic systoles were obtained by occluding the pulmonary artery during diastole by balloon inflation. The mean difference between isovolumic and auxotonic dP/dtmax is 40 mm Hg/sec (15 to 80 mm Hg/sec) - i.e. about 10% of the value measured auxotonically. Neither hemodynamic (pre- and afterload changes) nor inotropic changes influence this difference. Heart rate increase from 140 to 200/min also has no effect. This corresponds with the unchanged time interval between pulmonary valve opening and right ventricular dP/dtmax under all these conditions. Only heart rates below 100/min seem to enhance the difference between isovolumic and auxotonic dP/dtmax. Since the difference is not altered at various inotropic states, the result of this study leads to the conclusion that the relative changes in contractility could be slightly overestimated by using the auxotonic dP/dtmax for inotropic assessment. Practically, this inexactitude is within the error range of the method. Therefore, the use of dP/dtmax measured auxotonically does not introduce a marked disadvantage related to isovolumic dP/dtmax for assessment of relative inotropic changes of the right ventricle in isolated hearts.

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Causes of an extremely high local twinning rate.

The Romanian village Eftimie Murgu, until recently quite endogamous, shows a remarkably high total twinning frequency of 20% between 1927 and 1977. Some other demographic properties are unusual too: the secular development of twinning is not so much characterized by a steady frequency decline as by a sharp and temporary depression after World War II. The distribution of twins on maternal age and parity is not only characterized by an increase with age/parity but there is also a peak in the lowest ages/parities. The well-known higher fertility of twins' mothers is confirmed. In order to check the possible genetic determination of the high twin frequency, pedigrees of six to eight generations were reconstructed for every twin; moreover, twin frequencies of other isolated Romanian villages were examined for comparison. These data suggest that genetics is an important cause of twin births.

Adolescent↗
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An experimental evaluation of impedance cardiographic and electromagnetic measurements of stroke volumes.

The reliability of impedance cardiography for absolute and relative measurements of stroke volumes is assessed by comparing data with electromagnetic flowmeter measurements in 14 anaesthetized mongrel dogs. Cardiac output was altered in each dog (as much as possible) by a variety of physical and pharmacological interventions. Impedance cardiography does not provide absolute values for stroke volumes, although relative changes may be calculated with reasonable reliability if a correction factor ('CIMP') is employed. 'CIMP' is around 0 . 8 in subjects breathing spontaneously or when alternative pressure ventilation is applied. However, this factor can only be used in an intermediate range of stroke volumes (10-30 ml in the dog). At lower and higher cardiac output levels other correction factors must be observed accordingly. Intermittent positive pressure ventilation increases the sensitivity of relative stroke volume measurements by transthoracic impedance, leading to an average 'CIMP' of 1 . 5. For calculation of relative stroke volume changes by impedance cardiography, the simple formula: (formula; see text) is satisfactory instead of the more complicated Kubicek formula.

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