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Biomedical subjects

N Lewis

Publications and source records attributed to N Lewis.

At least 73 records · Page 4Linked to original sources
PubMed1981

Echocardiographic diagnosis of left anterior descending coronary artery disease and left ventricular asynergy.

Interventricular septal (IVS) motion was studied by M-mode echocardiography in 60 patients to review the value of the technique in identifying left anterior descending (LAD) coronary artery disease. Abnormalities of IVS thickening and excursion were presented in 90% of patients with proximal LAD disease, whereas septal function was essentially normal in patients with distal LAD disease and in patients with disease of the right and/or circumflex coronary arteries. Abnormalities of IVS motion were greater in patients with a history of previous anterior wall infarction and/or the presence of angiographic left ventricular (LV) asynergy. There was no difference between patients with isolated or combined LAD disease, nor was there a difference between patients with complete or partial obstruction of the LAD, when more than 75% of the lumen was occluded. The echo was also useful in identification of anterior LV asynergy. Abnormal widening of the LV near the apex and abnormal septal movement in this area detected, with high sensitivity and specificity, patients with angiographic anterior wall asynergy.

Arrhythmias, Cardiac↗
PubMed1980

Isovolumic relaxation period in man.

Isovolumic relaxation period (IRP) was measured noninvasively from the onset of the aortic component of the second heart sound on the phonocardiogram to the point of separation of the mitral leaflets on the echocardiogram. IRP was measured in 83 patients with different cardiac diseases. The duration of IRP was 58 +/- 11 msec. in normal subjects. It was prolonged in hypertension (p < 0.001), HOCM (p < 0.001), in aortic stenosis (p < 0.05), and aortic incompetence (p < 0.001), and was shortened in congestive cardiomyopathyl (p < 0.05) and mitral stenosis (p < 0.01). In patients with coronary artery disease and normal over-all systolic LV function, IRP was prolonged (p < 0.001); IRP was shortened in four patients with coronary disease who had severe LV dysfunction and severe additional mitral incompetence. IRP was related to systemic blood pressure, percentage shortening of the LV in systole, and to the mitral EF slope. It tended to increase with increasing heart rate and a regression equation was developed for predicting IRP in relation to blood pressure and heart rate in normal sbjects. There was no relation to the PR-Ac time or to isovolumic contraction time. IRP is a useful measurement of LV dynamics in early diastole.

Aortic Valve Insufficiency↗
PubMed1980

Left ventricular function in liver cirrhosis: an echocardiographic study.

Left ventricular (LV) size and function were studied by echocardiography and measurement of systolic time intervals in 14 patients with liver cirrhosis. There was a small increase in LV end-diastolic dimension, and an increase in systolic ventricular performance, calculated stroke dimension and stroke and cardiac indices. Mean blood pressure was low normal. Preejection period was shortened and the preejection period/LV ejection time ratio, decreased. The data indicate that patients with liver cirrhosis have mild LV enlargment, reduced peripheral resistance and an increase in mesurements of systolic LV performance.

Adult↗
PubMed1980

Effect of standing and squatting on echocardiographic left ventricular function.

The effects of changes in posture on left ventricular (LV) diameter and function were studied by echocardiography in 14 healthy children. On changing from the supine to the standing position, enddiastolic LV diameter decreased by 13 +/- 5% (P < 0.001), heart rate increased (P < 0.05) and calculated stroke index (-37 +/- 11%, P < 0.001) and cardiac index (-32 +/- 14%, P < 0.001) fell. There was not a significant change in the echocardiographic measurement. % delta s, mean Vcf and max Vpwm (ns) but mean Vcf increased in relation to mean blood pressure in 3 patients, suggesting an increase in LV contractility. Squatting was accompanied by an increase in LV cavity dimension (P < 0.001), while heart rate fell slightly and calculated stroke index (%35 +/- 28%, P < 0.001) and cardiac index (+33 +/- 27%, P < 0.001) increased. Mean blood pressure increased by 19 +/- 18% (P < 0.01). There was again no significant change in % delta s, mean Vcf and max Vpwm. Most patients fell on the control (supine) blood pressure--mean Fcf curve; in 2 patients there was a residual increase in sympathetic tone and LV contractility.

Adolescent↗
PubMed1979

Selection for ethanol tolerance in two populations of Drosophila melanogaster segregating alcohol dehydrogenase allozymes.

Selection for ethanol tolerance was equally successful in two populations of D. melanogaster in both of which the frequency of AdhF was 0.5 at the start of the experiment. Increased tolerance to ethanol was not invariably associated with increased frequencies of AdhF. In one population alcohol dehydrogenase (ADH) activity was significantly higher in three of the four selected sublines compared with their controls but there was no difference in activity between the selected and control sublines in the second population. The level of ADH activity in the control and selected lines was significantly correlated with the frequency of AdhF, but not with ethanol tolerance. These results show that adaptation to environmental alcohols in populations of D. melanogaster can be independent of the ADH system.

Alcohol Oxidoreductases↗
PubMed1979

Effect of postural changes on pulsus alternans: an echocardiographic study.

We describe a patient who had severe left ventricular dysfunction and pulsus alternans following an episode of severe viral myocarditis. Pulsus alternans was mild with the patient in the supine and squatting positions but increased dramatically on standing. Echocardiograms were used to study changes in left ventricular dimension and function with changes in posture. On standing, there was a decrease in the left ventricular diameter and an increase in the absolute and relative shortening fraction and the velocity of shortening on the strong beats, and there was a decrease in end-diastolic dimension and the measurements of ventricular contractility on the weak beats. The marked increase in pulsus alternans during standing may have been induced by increased sympathetic stimulation following the decrease in ventricular loading conditions, while the great beat-to-beat differences in end-diastolic dimension suggest, in addition, the importance of Starling's mechanism.

Adult↗
PubMed1979

Diagnostic value of cross-sectional echocardiography in left atrial myxoma.

Atrial myxoma is a rare condition that may have unusual clinical manifestations. Two patients with left atrial myxoma are described. One presented with paroxysmal nocturnal dyspnea and no abnormal physical signs on clinical examination; the second presented with palpitations and physical findings suggestive of mild mixed mitral valve disease. Echocardiography and cross-sectional echocardiography confirmed the diagnosis of atrial myxoma in both patients, and the tumors were successfully removed by operation. Cross-sectional echocardiography may obviate the need for cardiac catheterization in patients with left atrial tumors.

Echocardiography↗
PubMed1979

Effect of respiration on echocardiographic ventricular dimensions and relationship to the second heart sound.

The effects of normal respiration on echocardiographic right and left ventricular dimensions were studied in 8 normal subjects (group 1) and in 10 patients with ventricular volume overload due to anaemia (group 2). Right ventricular internal diameter (RVID) increased on inspiration in both groups of patients (group 1, 0.3 +/- 0.1 cm; group 2, 0.6 +/- 0.4 cm), while left ventricular internal diameter (LVID) decreased (group 1, 0.3 +/- 0.2 cm; group 2, 0.4 +/- 0.3 cm). The changes in echocardiographic diameter were related to the duration of electromechanical systole and to the changes in the splitting of the second heart sound; there was a linear relationship between RVID and Q--P2 (P less than 0.001) and A2--P2 (P less than 0.001). Echocardiographic measurements of cardiac chamber size should take into account the changes which occur during respiration.

Adolescent↗
PubMed1979

Asbestosis.

Explore the source record for details and available documents.

Asbestosis↗
PubMed1978

Variation in amount of enzyme protein in natural populations.

Among strains of Drosophila melanogaster each derived from a single fertilized female taken from natural populations, there is variation in both alcohol dehydrogenase (ADH) activity and the amount of ADH protein. The correlation between ADH activity and number of molecules over all strains examined is 0.87 or 0.96 in late third instar larvae depending on whether the substrate is 2-propanol or ethanol. With respect to the two common electrophoretic allozymic forms, F and S, segregating in these populations, the FF strains on the whole have higher ADH activities and numbers of ADH molecules than the SS strains. Over all strains examined, enzyme extracts from FF strains have a mean catalytic efficiency per enzyme molecule higher than that of enzyme extracts from SS strains when ethanol is the substrate, and much higher when 2-propanol is the substrate. One FF strain had an ADH activity/ADH protein ratio characteristic of SS strains.

Alcohol Oxidoreductases↗
PubMed1976

Otitis media and linguistic incompetence.

In the examination of some effects of chronic middle ear disorders on the development of auditory processing skills in socioculturally disadvantaged children, three groups of children received a battery of tests assessing speech hearing in quiet, speech hearing in noise, auditory discrimination, phonemic synthesis, dichotic listening, verbal intelligence, and nonverbal intelligence. The experimental group consisted of 14 Australian aboriginal children with histories of chronic middle disorder, whereas two control groups, one European and the other aboriginal, each contained 18 children with normal middle ear function. The results demonstrated that chronic middle ear impairment not only restricts the development of some auditory processing skills, but distorts their integrational pattern.

Audiometry↗
PubMed1975

Binaural hearing aids: are they dangerous for children?

We report a case in which a child suffered apparently permanent damage to residual hearing due to use of a powerful hearing aid. After review of the literature on damage to residual hearing by powerful hearing aids, we suggest that due caution should be observed in the prescription and monitoring of hearing aid usage for hearing-impaired children. Uncritical advocacy of powerful binaural aids is challenged as a potentially dangerous practice.

Adolescent↗
PubMed1975

Open-ended tympanometric screening: A new concept.

We introduce the concept of open-ended, successive-day, tympanometric screening. In impedance screening of children for middle ear disorders, there is a serious risk of over-referral if decisions are made on the basis of a single tympanogram. Serial tympanometric studies of Australian aboriginal children show that, whereas the type B tympanogram is usually stable, type A and type C patterns are prone to vary from day to day, inviting inappropriate referral decisions unless the classifications are confirmed by tests on successive days.

Adolescent↗
PubMed1969

Lipid metabolism in human platelets. II. De novo phospholipid synthesis and the effect of thrombin on the pattern of synthesis.

Washed human platelets were incubated with radioactive glycerol; the platelets were able to synthesize de novo the major phosphoglycerides including phosphatidic acid, phosphatidylinositol, phosphatidyl choline, phosphatidyl ethanolamine, and phosphatidyl serine. The specific activities of the phosphoglycerides obtained after glycerol incorporation indicate that phosphatidic acid, phosphatidylinositol, and phosphatidyl choline are metabolically active relative to phosphatidyl ethanolamine and that formation of phosphatidyl serine occurs to a much more limited extent. When platelets were incubated with bovine thrombin, 1 U/ml, the pattern of glycerol incorporation into phospholipid was changed. There was a 3-fold decrease in the total incorporation into lipid in 30 min with a relative 5-fold decreased incorporation into phosphatidyl choline and phosphatidyl ethanolamine and a 5-fold increased incorporation into phosphatidyl serine. The increased incorporation into phosphatidyl serine. The increased incorporation into phosphatidyl serine was maximal within the first 2 min but was transient, since within 20 minutes, the rate returned to that seen in platelets incubated with glycerol alone. Purified human thrombin also produced this same effect on phospholipid synthesis in platelets. Trypsin produced effects on phosphoglyceride formation similar to those seen with thrombin, and the trypsin-induced effect was inhibited by prior incubation of trypsin with soybean trypsin inhibitor, suggesting that proteolysis may be required for the observed effects on phospholipid synthesis.

Acetates↗