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Biomedical subjects

L McDonald

Publications and source records attributed to L McDonald.

At least 73 records · Page 4Linked to original sources
PubMed1985

Genes for insulin I and II, parathyroid hormone, and calcitonin are on rat chromosome 1.

Insulin, parathyroid hormone, and calcitonin are polypeptide hormones that regulate important physiological processes in target tissues. Rat genes encoding each hormone were chromosomally assigned to rat chromosome 1. Both rats and mice have two insulin genes (I and II). However, in contrast to mice in which insulin I and II are asyntenic, rat insulin I and II were both localized to chromosome 1. This study identifies a conserved syntenic group on rat chromosome 1, and implies that mouse insulin I and II genes were chromosomally separated after rats and mice diverged 20-35 million years ago.

Animals↗
PubMed1985

Localization of the human prealbumin gene to chromosome 18.

A human liver cDNA library was screened using an oligonucleotide probe based on the amino acid sequence of human prealbumin. The cDNA insert of one positive clone was sequenced and found to contain the entire coding sequence of human prealbumin plus untranslated 5' and 3' regions. This cDNA was used to probe DNA from a panel of mouse/human somatic cell hybrids. Only those hybrids containing human chromosome 18 showed the human-specific hybridization pattern, thereby localizing the human prealbumin gene to this chromosome.

Amino Acid Sequence↗
PubMed1985

Prevention of metabolic alkalosis induced by gastric fluid loss using H2 receptor antagonist.

Gastric fluid loss is a common cause of metabolic alkalosis. We studied various acid-base parameters in 20 patients undergoing continuous nasogastric (NG) suctioning for periods ranging from 3 to 17 days. Ten patients received cimetidine 300 mg intravenously every 6 hr (cimetidine-treated group). The remaining 10 patients received an antacid compound through the NG tube (control group). The rise in plasma bicarbonate concentration was significantly greater in the control group as compared to the cimetidine-treated group. As expected, gastric acid output was considerably lower in the cimetidine-treated group than in the control group. We conclude that cimetidine administration may be used in preventing metabolic alkalosis associated with gastric fluid loss by inhibiting gastric secretion of HCl.

Adolescent↗
PubMed1985

Biochemical and neuropsychological effects of elevated plasma phenylalanine in patients with treated phenylketonuria. A model for the study of phenylalanine and brain function in man.

Phenylketonuria provides a human model for the study of the effect of phenylalanine on brain function. Although irreversible mental retardation is preventable through newborn diagnosis and dietary phenylalanine restriction, controversy exists regarding the effects of increased concentrations of phenylalanine in older patients. We have studied ten older, treated, phenylketonuric patients using a triple-blind, multiple trials, crossover design. Each patient was tested at the end of each of three 1-wk periods of high or low phenylalanine intakes. Tests included a repeatable battery of neuropsychological tests, analysis of plasma amino acids, and measurement of urine amino acids, phenyl organic acids, dopamine, and serotonin. In all 10 patients plasma phenylalanine rose (900-4,000 microM). In 9 of 10 patients there was an inverse relationship between plasma phenylalanine and urine dopamine excretion. When blood phenylalanine was elevated, these patients had prolonged performance times on neuropsychological tests of higher but not lower integrative function. Urinary serotonin fell during phenylalanine loading in six patients. The concentration of phenylacids in the urine was not proportional to the plasma phenylalanine at concentrations below 1.5 mM. In one patient, neither performance time nor dopamine excretion varied as blood phenylalanine rose or fell. We interpret these data as follows: blood phenylalanine above 1.3 mM impairs performance on neuropsychological tests of higher integrative function, this effect is reversible, and one mechanism may involve impaired biogenic amine synthesis.

Adolescent↗
PubMed1984

An evaluation of two-dimensional echocardiography in the diagnosis of hypertrophic cardiomyopathy.

Various anatomical and functional features of hypertrophic cardiomyopathy are analyzed in view of the data provided by two-dimensional echocardiography. Measurement of septal thickness is crucial, and is best done by a combination of M-Mode and 2-D echo. Two types of systolic anterior movement of the mitral valve (SAM) are observed and are related to the degree of subvalvular gradient. The specificity of these patterns of SAM is analyzed. The functional anatomy of the mitral valve in relation to the presence and degree of mitral regurgitation shows that although the presence and type of SAM are important, there are other causes of mitral regurgitation in hypertrophic cardiomyopathy unrelated to SAM. We emphasize the fact the 2-D echo cannot "diagnose" hypertrophic cardiomyopathy except when cardiac hypertrophy plus SAM involving the body of the mitral valve is seen; in the remaining cases, 2-D echo confirms/suggests the clinical diagnosis.

Cardiomyopathy, Hypertrophic↗
PubMed1983

The mechanism of mitral regurgitation in dilated left ventricle.

To assess the mechanism of mitral regurgitation in ventricular dilatation, 24 patients with dilated cardiomyopathy (13 with and 11 without mitral regurgitation) and 10 normal individuals were studied by two-dimensional echocardiography. Left ventricular dimensions and mitral ring diameters in systole and diastole were measured in the long-axis section, and systolic interpapillary muscle distance in the short-axis section. The results showed: Mitral ring diameter is increased in most patients with dilated cardiomyopathy. Neither increased ring diameter, reduced ring contraction, nor decreased interpapillary muscle distance determine the presence of mitral regurgitation. The only difference between those patients with and without mitral regurgitation was the degree of left ventricular dilatation (p less than 0.05).

Adult↗
PubMed1983

Ageism in the labor market: estimating earnings discrimination against older workers.

In this paper we attempt to determine the degree to which older persons employed full-time experience a decline in earnings not related to a decline in productivity. We label such a decline in earnings "discrimination." Using panel data for a cohort of men aged 45 to 54 in 1966, we examined trends in earnings between 1966 and 1976 and the effects of labor force experience on earnings controlling for factors related to productivity, such as health, time on the job, and specific occupational training, as well as other factors known to influence earnings levels. Comparing earnings attainment models estimated at both time periods, the effect of experience on earnings was negligible in 1966 but substantial and negative in 1976. By far the largest component in the real earnings decline experienced by these men between 1966 and 1976 was associated with the increase in age-related experience.

Age Factors↗
PubMed1983

Cross-sectional echocardiographic features of ruptured chordae tendineae.

Thirty-two patients with mitral regurgitation secondary to ruptured chordae tendineae were studied by cross-sectional echocardiography. Twenty of them subsequently underwent operation. Three signs are described. (1) Non-coaptation of the leaflets (55%). (2) Systolic fluttering echo in the left atrium originating from the mitral valve (20%). (3) A previously not described small diastolic chaotically moving echo in the short axis section of the left ventricle at the level of the papillary muscles (65%). The combined sensitivity of these three signs was 85%. The specificity of the three signs when compared with those of 107 patients with mitral regurgitation of different aetiologies studied by cross-sectional echocardiography was 99%, 100% and 99%, respectively. Six patients were studied after mitral valve repair; restriction of the surgical treated leaflet and reduction of its valve area was seen in all of them, and the disappearance of the valvar signs of ruptured chordae noted. The persistence of the small echo sign in the short axis of the left ventricle indicated its chordal origin.

Chordae Tendineae↗
PubMed1983

Systolic anterior motion of the mitral valve in hypertrophic cardiomyopathy. A cross-sectional echocardiographic study.

UNLABELLED: Different cross-sectional echocardiographic patterns of systolic anterior motion of the mitral valve (SAM) have been observed in patients with hypertrophic cardiomyopathy. chordae tendineae and/or the free edge of the mitral valve were seen to be involved in some: SAM(c). The body of the mitral valve encroached upon the left ventricular outflow tract in this movement in a second group: SAM(v). Other patients did not show SAM. A study of 27 patients was performed to investigate the relationship of these patterns of SAM to the subaortic gradient as well as the prevalence and degree of mitral regurgitation. The absence of SAM correlated with no obstruction and 29% prevalence of mitral regurgitation. In SAM(c), the mean gradient was 10 +/- 10 mmHg. (0-35 mmHg), and mitral regurgitation involved 36% of the patients. In SAM(v) the mean gradient found was 81 +/- 37 mmHg (20-150), and 67% had mitral regurgitation. In situations where mitral regurgitation was most prevalent its degree was greatest. IN CONCLUSION: (1) chordal or leaflet participation in SAM is relevant to the presence and degree of obstruction; (2) leaflet involvement usually implies severe obstruction; (3) distortion of the mitral valve apparatus may contribute to the genesis of mitral regurgitation.

Adolescent↗
PubMed1983

Prolapse of the mitral valve in secundum atrial septal defect: a functional mechanism.

Prolapse of the mitral valve in patients with secundum atrial septal defect has been described angiographically and by two-dimensional echocardiography. It has been suggested that prolapse of the mitral valve in these patients is due to distortion of left ventricular shape and small left ventricular volume. To test this hypothesis 10 patients with unrepaired secundum atrial septal defect and 10 patients who had undergone repair of the defect were studied by two-dimensional echocardiography. The prevalence of mitral valve prolapse was 80% in the unrepaired group and 20% in the repaired group (P less than 0.01). Short axis of the left ventricle revealed septal bulging into the left ventricle, the end-diastolic ratio of minor to major axis being 0.71 in the unrepaired group and 0.93 in the repaired group (P less than 0.001). Systolic and diastolic cross-sectional areas were larger in the repaired group compared with the unrepaired group (P less than 0.05). Prolapse of the mitral valve in patients with secundum atrial septal defect may be related to the distorted left ventricular shape and small left ventricular volume.

Adolescent↗
PubMed1983

Different mechanisms of mitral regurgitation in acute and chronic forms of coronary heart disease.

Contradictory two-dimensional echocardiographic findings have been reported in relation to the role of prolapse of the mitral valve and lack of systolic leaflet coaptation in mitral regurgitation secondary to coronary heart disease. A prospective study of 22 patients with chronic coronary heart disease and mitral regurgitation showed the following: Inferior akinesia was detected in 14 (64%), fibrosis of the postero-medial papillary muscle in 10 (45%), and prolapse of the mitral valve in nine (41%). A combination of the three signs was seen in six patients (27%). Lack of systolic leaflet coaptation was seen in only two patients, both with anterior myocardial infarction. When these results are compared with those reported in the literature, it is apparent that in acute coronary heart disease, lack of leaflet coaptation is frequently visualized (P less than 0.01) and fibrosis of the postero-medial papillary muscle and prolapse of the mitral valve are lacking (P less than 0.01). A unitary explanation of all forms of mitral regurgitation in coronary heart disease is misleading; mechanisms of mitral regurgitation in coronary heart disease depend on the clinical presentation--acute or chronic, the site of infarction, and the presence of cardiac dilatation.

Adult↗
PubMed1982

Anaesthesia in first degree atrioventricular block.

A patient with an intracardiac conduction defect characterised by first degree atrioventricular block due to slowed transmission through the atrioventricular node with increased refractoriness of the node, is described. Asymptomatic first degree block, rarely progressing to transient Wenckebach (type 1 second degree) block had been present for a period of 32 years until general anaesthesia was required, when profound bradycardia attributable to complete atrioventricular block developed abruptly. Subsequent investigations located delayed intracardiac conduction through the atrioventricular node, and indicated excess vagal activity rather than structural disease as the cause. The significance of first degree heart block is discussed in relation to other forms of atrioventricular conduction defect and the current recommendations for temporary pacing for elective general anaesthesia.

Anesthesia, General↗