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Biomedical subjects

A L Davis

Publications and source records attributed to A L Davis.

At least 55 records · Page 3Linked to original sources
PubMed1984

Ascending aortic blood velocity and acceleration using Doppler ultrasound in the assessment of left ventricular function.

We have used a 2.2 MHz continuous-wave Doppler blood velocity meter (Bach-Simpson BVM 202) to measure ascending aortic blood velocity and acceleration, and have obtained from the velocity signal a noninvasive measure of stroke volume and cardiac output by combining the Doppler technique with M-mode echocardiography. In two separate studies we have systematically altered the loading conditions of the heart with lower body pressure; and the inotropic state of the heart with dobutamine (5 micrograms . kg-1 . min-1), and documented the changes in mean velocity (MV), maximum acceleration (MA), stroke volume (SV), cardiac output (CO) and left ventricular end-diastolic dimension (EDD) (M-mode echocardiography). Application of lower body pressure to subjects in a 30 degrees head-up tilt position caused a systematic increase in preload, as shown by a 9% increase in EDD, which raised SV by a maximum of 33% (p less than or equal to 0.001) and CO by 32% (p less than or equal to 0.01), thus showing a classical Starling response; whilst there was relatively little increase in MA. Conversely, infusion of dobutamine, an inotropic agent, caused a 29.2% increase in MA (p less than or equal to 0.01) with minimal increase in SV. Thus, the ability to measure ascending aortic blood velocity allows noninvasive monitoring of changes in both inotropic state and Starling function, with considerable ease and rapidity.

Adolescent↗
PubMed1984

Self-help smoking cessation and maintenance programs: a comparative study with 12-month follow-up by the American Lung Association.

One thousand two hundred thirty seven smokers responding to lung association announcements in five geographic areas were randomly assigned to one of four groups and mailed American Lung Association materials: 1) leaflets (L); 2) leaflets plus maintenance manual (L + M); 3) cessation manual (C); and 4) cessation and maintenance manuals (C + M). Five telephone interviews over one year achieved a 95 per cent follow-up completion rate. Nonrespondents as well as exclusive cigar and pipe users were classified as smokers. Twenty per cent quit initially, with 5 per cent continually abstinent in (C + M) at 12 months vs 2 per cent in (L) (p less than .05). Nonsmoking prevalence rates (no tobacco smoking in the past month), on the other hand, gradually increased after six months; at 12 months those with the maintenance component, (L + M) and (C + M), had higher rates (18 per cent) than (L) (12 per cent) or (C) (15 per cent). Leaflets and manual alone were least cost effective. Rising nonsmoking prevalence rates observed in all groups suggest that successful attempts to quit increased over time and that a contributing factor might have been the follow-up method. Although achieving lower quit rates than methods requiring attendance at a course, the self-help intervention has the advantages of greater availability, flexibility, and in some instances lower cost.

Cost-Benefit Analysis↗
PubMed1978

In vitro antimicrobial activity of some cyclic hydroxamic acids and related lactams.

Against Enterobacter aerogenes 13048, Serratia marcescens 13880, Klebsiella pneumoniae 10031, Pseudomonas aeruginosa 10145, Escherichia coli 9723, Lactobacillus casei 7469, Lactobacillus plantarum 8014, Leuconostoc dextranicum 8086, and Streptococcus faecalis 8043, the mean minimal inhibitory concentrations of three cyclic hydroxamic acids, 3-amino-3,4-dihydro-1-hydroxycarbostyril, the 6-chloro analog, and the 7-chloro analog, were 0.6, 0.6, and 0.2 micrograms/ml, and those of the corresponding lactams, 3-amino-3,4-dihydrocarbostyril, the 6-chloro analog, and the 7-chloro analog, were 60, 60, and 6 micrograms/ml, respectively. Under the same assay conditions the mean minimal inhibitory concentrations of chloramphenicol and kanamycin were both 2 micrograms/ml. In addition, the cyclic hydroxamic acids but not the lactams inhibited the growth of Candida albicans at minimal inhibitory concentrations ranging from 20 to 200 micrograms/ml, at pH 7, as compared with that of amphotericin B, at 2 micrograms/ml.

Anti-Bacterial Agents↗
PubMed1977

Respiratory modulation of baroreceptor and chemoreceptor reflexes affecting heart rate through the sympathetic nervous system.

1. Brief stimuli were delivered to the carotid body chemoreceptors or the carotid sinus baroreceptors at different phases of the respiratory cycle in anaesthetized dogs. Chemoreceptor stimulation was achieved by injecting small volumes (0.2-0.5 ml.) of warmed saline equilibrated with CO(2) near to the carotid bodies on both sides. Baroreceptor stimulation was achieved by injecting larger volumes (2-5 ml.) of saline equilibrated with air into the region of the carotid bifurcation on both sides, after first clamping the common carotid arteries.2. When the vagus nerves were intact, but sympathetic nervous effects on heart rate were blocked by administration of propranolol, there was a prompt and pronounced bradycardia evoked when either baroreceptor or chemoreceptor stimuli were given in expiration, but little or no change in heart rate when they were given in inspiration.3. When the vagus nerves were cut, but sympathetic nervous function was intact, respiratory modulation of both baroreceptor and chemoreceptor reflex effects on heart rate could still be demonstrated. The bradycardia evoked by either stimulus was more marked for stimuli given in expiration than for stimuli given in inspiration. A complementary response pattern for brief decreases in baroreceptor stimulation (carotid occlusions) was demonstrated: the tachycardia evoked by occlusions timed during inspiration was greater than that evoked by occlusions timed during expiration. All the reflex effects were mediated by the sympathetic system because they were abolished by administration of propranolol.4. Typically, the sympathetic reflex effects were slight in comparison with the vagal reflexes evoked by either chemoreceptor or baroreceptor stimuli.

Animals↗
PubMed1976

Synthesis and microbiological activities of beta-(1-chloro-2-naphthyl) alanine and beta-(1-bromo-2-naphthyl) alanine.

beta-(1-Chloro-2-naphthyl)alanine and beta-(1-bromo-2-naphthyl) alanine were synthesized by ammonolysis of the corresponding alpha, 1-dihalo-2-naphthalenepropanoic acids derived from 1-nitro-2-naphthylamine by diazotization and condensation with acrylic acid in the presence of cuprous halides. The two analogs as well as the previously reported beta-(2-naphthyl)alanine and beta-(1-naphthyl)alanine were studied as growth inhibitors of Escherichia coli 9723, Leuconostoc dextranicum 8086, and Lactobacillus plantarum 8014. In general, the chloro and bromo analogs were more effective than the unsubstituted naphthylalanines as growth inhibitors of the three microorganisms studied.

Alanine↗
PubMed1975

Synthesis and microbiological activities of some monohalogenated analogs of tyrosine.

2-Chlorotyrosine and 2-bromotyrosine, as well as the previously reported 2-fluorotyrosine, were synthesized by hydrolysis of the condensation products from the appropriate benzyl bromide and ethyl acetamidomalonate and were compared with the corresponding 3-halotyrosines as growth inhibitors of Escherichia coli 9723, Streptococcus faecalis 8043 and Lactobacillus plantarum 8014. In contrast to the 2- and 3-fluorotyrosines which were equally effective as growth inhibitors, the 2-chloro- and 2-bromotyrosines were much more effective than the 3-chloro- and 3-bromotyrosines in inhibiting the growth of the three microorganisms. For each of the assay organisms, the growth inhibitions of all three 2-halotyrosines were reversed competitively in varying degrees by tyrosine.

Bromine↗
PubMed1975

Synthesis and antibacterial activities of some chloro analogs of 3 amino-3,4-dihydro-1-hydroxycarbostyril.

The effects of a chloro substituent upon the microbiological activities of 3-amino-3,4-dihydro-1-hydroxycarbostyril were determined. The 5-, 6-, and 7-chloro analogs were synthesized by reductive cyclizations of the appropriately chloro-substituted o-nitrophenylalanines, while the 8-chloro analog was obtained from the N-trifluoroacetyl-3-chloro-2-nitrophenylalanine ethyl ester. All of these compounds were observed to inhibit the growth of Escherichia coli 9723, Leuconostoc dextranicum 8086, and Lactobacillus plantarum 8014. The relative inhibitory activities of the chloro analogs were 7-Cl greater than 6-Cl greater than 8-Cl greater than 5-Cl in E. coli and 7-Cl greater than 6-Cl greater than 8-Cl = 5-Cl in L. dextranicum and L. plantarum. In each of the three microorganisms, the 7-Cl analog was a more effective growth inhibitor than the parent unsubstituted compound. The growth inhibitory activities of this class of compounds were demonstrated to be much more effective than those of the four corresponding lactams, the 5-, 6-, 7-, and 8-chloro analogs of 3-amino-3,4-dihydrocarbostyril.

Anti-Bacterial Agents↗