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Biomedical subjects

M Tynan

Publications and source records attributed to M Tynan.

At least 127 records · Page 7Linked to original sources
PubMed1975

Post-natal developmental changes in the length-tension relationship of cat papillary muscles.

The length-tension relationship and the effect of paired electrical stimulation were studied in right ventricular papillary muscles obtained from cats. The animals were divided into three age groups: neonatal kittens, less than 24 hr of age; infant kittens, 16--18 days of age; and adult cats. 2. The muscles were electrically driven to contract isometrically using field stimulation at 10--20% above the threshold valus. 3. At Lmax the neonatal preparations produced significantly less developed (active) tension than did the adult preparations. The resting tension at Lmax was significantly greater in the neonatal preparations than in the adult ones. The infant group occupied an intermediate position between the two other groups. 4. The response to paired electrical stimulation was less in the neonatal group than in either the infants or the adults. 5. It is concluded that post-natal developmental changes occur in the contractile properties of the myocardium of the cat.

Age Factors↗
PubMed1975

Ejection phase indices of left ventricular performance in infants, children, and adults.

A validatory study of quantitative single plane left ventricular cineangiography is presented, using human left ventricular casts ranging in size from 1.6 to 135 ml. Good correlation was found between actual and calculated volumes (r=0.967). 62 patient studies were carried out and the value of the usually calculated indices of left ventricular performance were compared to one another. Ejection fraction and mean rate of circumferential fibre shortening (mean Vcf) were found to be the best discriminators of abnormal left ventricular function, and, on the basis of the presented data, it is suggested that mean Vcf is the more sensitive index of left ventricular performance.

Adolescent↗
PubMed1975

Studies in a newborn infant with supraventricular tachycardia and Wolff-Parkinson-White syndrome.

A neonatal patient with Wolff-Parkinson-White type A and supraventricular tachycardia is described. Demonstration of the mechanism of the tachycardia and its termination were achieved using intracardiac electrography and cardiac pacing. Quantitative left ventricular angiography and echocardiography showed impaired left ventricular function following the arrhythmia. Serial echocardiograms demonstrated the subsequent return to normal left ventricular performance.

Angiocardiography↗
PubMed1975

Bidirectional tachycardia in a child. A study using His bundle electrography.

This is a report of a case of bidirectional tachycardia in a 6-year-old girl with no evidence of any structural abnormality of the heart. The patient had never received digitalis. The arrhythmia appeared to be precipitated by effort and emotional stress, and could be induced by increasing the heart rate by atrial pacing or isoprenaline administration. His bundle electrography showed that the arrhythmia was ventricular in origin. This emphasizes the importance of recording an effort electrocardiogram in all children with unexplained syncopal episodes, even when the resting electrocardiogram is normal.

Bundle of His↗
PubMed1975

Validity of echocardiographic estimates of left ventricular size and performance in infants and children.

Echocardiography has been shown to be a reliable method for estimating left ventricular size and function in adults, but little attention has been paid to its application to infants and children. This paper describes a validatory study in 40 children aged between 4 days and 16 years. There was a significant correlation between angiocardiographic and echocardiographic estimates of left ventricular end-diastolic volume (r=0.76), left ventricular end-systolic volume (r=0.68), and ejection fraction (r=0.73). Left ventricular mean circumferential shortening rate (mean Vcf), however, gave the mostsignificant correlation (r=0.91). These findings indicate that while care must be exercised in interpreting indices of left ventricular size and performance derived from echocardiography, these measurements, and in particular mean Vcf, do offer a useful and reliable means of assessing left ventricular function in infants and children.

Adolescent↗
PubMed1975

Seasonal and sexual variations in the responsiveness of rabbit hearts to prolactin.

Rabbit hearts perfused by the Langendorff technique were studied. The addition of ovine prolactin (NIH-P-S-10) to the perfusate in a concentration of 50 ng/ml produced rapid increases in both the amplitude and rate of contraction in 33 adult male hearts studied in winter. Prepubertal male animals showed no response, and only 1 out of 12 adult females responded. Pretreatment for 10 days with 2.5 mg/day testosterone propionate led to minimal inotropic but not chronotropic responses in 2 out of 4 prepubertal males and 2 out of 4 adult females to prolactin. Clear responses to prolactin were seen in 5 adult males pretreated with reserpine. Propanolol consistently reversed both the inotropic and chronotropic actions of prolactin. The original experiments were performed in January and February. When tested in May, adult males failed to respond to prolactin and this situation, persisted until October when responsiveness again appeared. The same prolactin preparation and procedures were used throughout indicating that the changes must have been due to seasonal variations in the cardiac responsiveness to the hormone.

Animals↗
PubMed1974

Actions of prolactin and frusemide on heart rate and rhythm.

Rat hearts with coronary circulations perfused by the Langendorff technique were studied. Recordings were made of the electrical and mechanical activity. Once the rate and rhythm of each heart and stabilized it was perfused with Ringer-Locke solution for 90 minutes; frusemide (40 mug/ml) was added to the perfusate during the last 30 minutes of this period. Eighteen experiments were performed-six controls, six in which prolactin at a concentration of 50 ng/ml was added to the perfusate for the whole 90 minutes, and six in which a prolactin concentration of 200 ng/ml was used.With the controls heart rate and rhythm remained steady, but there was a slow decline in amplitude of the contraction. With a prolactin concentration of 50 ng/ml the heart rate rose to about 40% above control during the first hour and after an initial sharp increase the contraction amplitude declined more rapidly than in the controls. The prolactin concentration of 200 ng/ml produced a decline of about 25% in heart rate over the first hour and amplitude behaved much as in the controls. Frusemide had no clear effect on the rate of beating of the controls, but it tended to reverse both the acceleration produced by 50 ng/ml prolactin and the slowing produced by the higher dose. Both the doses of prolactin consistently caused disturbances of rhythm. These effects occur at concentration of prolactin found in human plasma in various pathophysiological conditions.

Animals↗