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Biomedical subjects

S E Kirkpatrick

Publications and source records attributed to S E Kirkpatrick.

51 records · Page 3Linked to original sources
PubMed1977

Patent ductus arteriosus in preterm infants with idiopathic respiratory distress syndrome. Radiographic and echocardiographic evaluation.

Clinical, radiographic, echocardiographic and operative findings were evaluated in 55 preterm infants with idiopathic respiratory distress syndrome (IRDS) complicated by patent ductus arteriosus (PDA). Pulmonary plethora was detected prior to age seven days in 52 infants, and prior to murmur detection in 42 infants. In those with large shunts, only 35% had cardiomegaly while 78% had a significant increase in cardiothoracic ratio (C/T) on sequential radiographs. Moreover, within 48 hours after ligation, 91% of infants had a significant decrease in C/T. Echocardiographic left atrial to aortic ratio (LA/Ao) was elevated in 71% with large shunts. In one patient with a large shunt there was neither a sequential increase in C/T nor an increased LA/Ao. Severity of left-to-right shunting across a PDA in the newborn was reliably gauged by combined radiographic and echocardiographic evaluation. Either modality alone failed to reflect the presence of a large volume shunt in a number of infants.

Ductus Arteriosus, Patent↗
PubMed1977

Renal responses of the fetal lamb to fetal or maternal volume expansion.

Fetal and maternal glomerular filtration rate (GFR), renal plasma flow (RPF), urine volume, sodium excretion, and fractional sodium reabsorption were measured in a chronically instrumented sheep preparation. Fetal GFR was essentially stable between 110 and 135 days of gestation (term = 147 days). There was a significant increase in GFR after 135 days. After the infusion of 50 ml of normal saline over a 30-minute period, fetal GFR and sodium excretion increased significantly. Fractional sodium reabsorption was significantly decreased. Thus, the fetus is capable of responding to volume expansion with saline with an increase in GFR and a decrease in fractional sodium reabsorption. After the infusion of 1000 ml of normal saline into the ewe in 1 hour, maternal GFR and RPF rose significantly. Sodium excretion rose 6-fold and fractional sodium reabsorption fell significantly. After the infusion of saline into the ewe, there was no change in fetal GFR, RPF, sodium excretion, urine volume, or fractional sodium reabsorption. Since there were no changes in fetal renal function after maternal volume expansion with saline there was no evidence for the transplacental passage of a natriuretic factor from ewe to fetus.

Animals↗
PubMed1976

Acute effects of maternal ethanol infusion on fetal cardiac performance.

In adult animals and man, both acute and chronic ethanol intake is associated with depression of myocardial performance. Accordingly, the cardiac effects of maternal ethanol infusions, in a manner comparable to common obstetric practice of inhibition of premature labor with ethano mighte for inhibition of premature labor, were evaluated in six chronically instrumented fetal sheep. Fetal and ewe arterial PO2, PCO2, and pH values remained within normal limits with infusion rates of 15 c.c. per kilogram of 10 per cent ethanol over two hours (blood ethanol = 110 mg. per cent) and 15 c.c. per kilogram over one hour (blood ethanol = 210 mg. per cent). Fetal instrument evaluation (for 14 to 30 days after operation) provided data concerning pressures and cardiac dimensions which allowed analysis of left ventricular performance. Ethanol produced a significant depression of the extent (p less than 0.01) and velocity (p less than 0.001) of left ventricular myocardial fiber shortening as well as in the mean rate of left ventricular myocardial fiber shortening as well as in the mean rate of left ventricular circumferential fiber shortening (p less than 0.01). These indices of cardiac contractility were depressed in the absence of changes in end diastolic diameter, left atrial pressure, and systemic arterial pressure. Thus, the practice of inhibition of premature labor with ethano6 might contribute to depressed myocardial performance in the neonatal period.

Animals↗
PubMed1976

Pharmacologic closure of patent ductus arteriosus in the premature infant.

The prostaglandins affect smooth-muscle tone of the ductus arteriosus. Patent ductus often complicates the clinical course of prematurely born infants with respiratory-distress syndrome. In the present study, a single oral or rectal dose of a potent inhibitor of prostaglandin synthesis, indomethacin, was administered to six consecutive premature infants with the syndrome who would otherwise have undergone surgical ligation of the patent ductus. Within 24 hours all the clinical symptoms and physical, echocardiographic and radiographic signs attributable to substantial left-to-right shunting through a patent ductus arteriosus dramatically and permanently disappeared. A transient reduction in renal function was observed in two infants in whom sustained ill-effects did not occur. The observation that constriction and closure of the patent ductus arteriosus may be induced pharmacologically raises important possibilities for the improved treatment of the respiratory-distress syndrome.

Cyclooxygenase Inhibitors↗
PubMed1976

Distribution of fetal cardiac output: importance of pacemaker location.

Important questions exist about the relative roles of changes in heart rate versus extent of myocardial shortening in regulating fetal cardiac output, because increases in heart rate created by left atrial pacing have been shown to increase right ventricular output and decrease left ventricular output. Since the pacemaker site could importantly influence foramen ovale flow and, hence, each ventricle's output, changes in individual ventricular outputs were examined when both the right and left atria were paced at a rate of 270 beats/min in five acute and in eight chronically instrumented fetal lamb studies. With pacing of either atrium, total cardiac output was unchanged compared to control values. However, the right ventricle contributed more to total cardiac output with left atrial pacing (73% acute, 65% chronic) than with right atrial pacing (51% acute, 57% chronic). Converse changes were observed in left atrial pacing (27% acute, 35% chronic) as compared to right atrial pacing (49% acute, 43% chronic). Thus the disparity that exists normally in the contributions of the right and left ventricles to total cardiac output is accentuated with left atrial pacing and minimized with right atrial pacing. Pressure measurements demonstrated changes in the atrial pressure relations that would be expected to alter flow across the foramen ovale depending on the chamber initially activated. Previous experimental differences can, therefore, be attributed to changes in the magnitude of shunting across the foramen ovale and depend on pacemaker location.

Animals↗
PubMed1976

Frank-Starling relationship as an important determinant of fetal cardiac output.

The importance of the Frank-Starling mechanism was evaluated in seven chronically instrumented fetal lambs (128-141 days gestation). Continuous determinations of left ventricular (LV) internal dimensions and pressures were obtained while LV end-diastolic diameter (LVEDD) was reduced by superior vena cava occlusion and increased by infusion of fetal blood into left atrium. A highly significant relationship was found to exist between stroke volume and LV extent of shortening (delta D) (r = + 0.99, P less than 0.001). Altering LVEDD from 10,5 to 13mm or LV end-diastolic pressure from 2.5 to 8 mmHg resulted in a 68% augmentation, in delta D. Spontaneous respiratory efforts resulted in frequent beat-to-beat variations in LVEDD and delta D, which maintained cardiac output constant over a wide range of respiratory rates. Moreover, LV output determined by indicator-dilution techniques remained unchanged over a wide range of spontaneous heart rates (114-180 beats/min) as a result of changes in delta D appropriate to alterations in LVEDD. Thus, changes in resting myocardial fiber length are of fundamental importance in fetal cardiovascular homeostasis and, within physiologic limits, it is quite clear that the Frank-Starling mechanism is operative and effective in the fetal lamb;

Animals↗
PubMed1975

Echocardiographic recognition of ventricular septal aneurysm--a case report.

The noninvasive detection of an aneurysm of the interventricular septum may be predictive of spontaneous closure of a ventricular septal defect. Moreover, in patients with audible systolic clicks the distinction must be made between septal aneurysm and mitral valve prolapse. The current report describes the echocardiographic visualization and pattern of motion of an aneurysm of the membranous ventricular septum. The diagnosis was made by both single crystal and real-time cross-sectional, multiple crystal ultrasound techniques prior to catheterization. These findings from the basis of the present study.

Angiocardiography↗
PubMed1975

Influence of poststimulation potentiation and heart rate on the fetal lamb heart.

Isolated cardiac muscle techniques and studies of the chronically instrumented fetal lamb heart were employed to evaluate the ability of fetal myocardium to exhibit poststimulation potentiation. Isometric tension development and the response to paired electrical stimulation were significantly reduced in isolated fetal ventricular myocardium when compared to the adult (P less than 0.001). As in the adult, increasing stimulation frequency raised fetal isometric tension via an increase in the rate of rise of tension development in the presence of reduction in time-to-peak tension. In seven fetal lambs the left ventricle was chronically instrumented with endocardial ultrasonic crystals and a high-fidelity micromanometer. After a 2-wk recovery period, heart rate was increased by atrial pacing from an average control level of 150 to 300 beats/min. Left ventricular dP/dt increased progressively and then fell beyond a heart rate of 270/min. When comparable pre- and immediate postpacing beats were analyzed, a step-wise increase in the velocity of left ventricular shortening and the mean rate of circumferential fiber shortening was observed in association with an increase in the extent of shortening. Thus, increases in the frequency of contraction exert a significant positive inotropic effect on the fetal heart.

Animals↗
PubMed1975

In situ physiological study of the developing heart.

Studies on cardiac muscle and whole heart isolated from the fetal and newborn lamb and adult sheep reveal striking age-dependent differences in cardiac ultrastructure, passive and active length-tension properties, force-velocity relationships, the compliance characteristics of both ventricles, myocardial energetics, and in the development of myocardial autonomic control. Isometric force development and both the extent and velocity of shortening at any load are reduced in the fetus when compared with the adult because of age-related changes in the proportion of myocardial tissue consisting of myofilaments. The distensibility characteristics of both the left (LV) and right ventricles (RV) are comparable in the fetal lamb close to term. In the early newborn period the RV has compliance characteristics similar to the RV of the fetus, whereas the LV alters its stress-strain characteristics to resemble the adult. Most recently, methods have been developed for the chronic evaluation of fetal left ventricular function. Internal LV dimensions and pressures are monitored continuously from midgestation beyond delivery.

Age Factors↗