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Biomedical subjects

H T Davis

Publications and source records attributed to H T Davis.

36 records · Page 2Linked to original sources
PubMed1981

Inhibition and recovery of growth processes in roots of Pisum sativum L. exposed to 60-Hz electric fields.

Roots of Pisum sativum L. were chronically exposed in aqueous inorganic nutrient medium to 60-Hz electric fields between 140 and 490 V/m (growth medium conductivity approximately 0.08 S/m). The growth rate, meristematic mitotic index, and growth rate recovery of the roots were determined. At 140 V/m there was no perturbation in growth rate or mitotic index. At 430 V/m the growth rate and the mitotic index were reduced. The mitotic index had a maximum depression (approximately 55% of control), which occurred at 4 h. The depression in growth rate was immediate and constant over time. When roots were exposed to an electric field at 430 V/m for 2 days, the growth rate was depressed by about 40%. When the field was terminated, the growth rate steadily increased and was almost normal after 5 days. At 490 V/m root growth rate was almost completely arrested. According to these results, there is a narrow range of induced membrane potentials that span the range from slightly altered to almost completely arrested growth rates.

Electromagnetic Fields↗
PubMed1981

Digitalis-associated cardiac mortality after myocardial infarction.

The effect of digitalis therapy on 4-month posthospital cardiac mortality was investigated in 812 patients who survived the hospital phase of acute myocardial infraction. A stepwise multiple logistic regression analysis was used to identify variables associated with increased mortality and to adjust for differences in confounding variables between digitalis and nondigitalis patients. The major 4-month mortality (10 of 26 patients [38.5%]) occurred in digitalis-treated patients with congestive heart failure in the coronary care unit and complex ventricular premature depolarizations (VPDs) on the predischarge Holter recording. Logistic analyses that controlled for confounding variables indicated that digitalis use contributed to the increased mortality rate in this high-risk subset. The predicted mortality difference due to digitalis in patients with congestive heart failure and complex VPDs, adjusted for relevant nondigitalis risk factor variables, was 30% (90% confidence interval 18-42%). This retrospective study suggests that digitalis use increases the early posthospital mortality of myocardial infarction patients with combined electrical and mechanical dysfunction.

Aged↗
PubMed1980

Frequency and complexity of ventricular ectopic beats in the posthospital phase of myocardial infarction.

This study is a descriptive report of the occurrence of ventricular arrhythmias in a large, prospectively designed follow-up study of postcoronary patients. Six-hour Holter recordings were obtained on 954 postinfarction patients prior to hospital discharge and at 4 (n = 837), 8 (n = 762), 12 (n = 713), and 24 (n = 487) months post-discharge. Ventricular ectopic beats (VEB) were quantitated by frequency and patterns at each recording, and antiarrhythmic medication usage was recorded. The proportion of patients wtih each VEB frequency (any, less than 9.9/hour, 10 - 19.9/hour, greater than or equal to 20/hour) increased progressively during the 24-month follow-up, with the most significant increase in the interval between baseline and the four-month follow-up recording. Significant (p less than 0.01) associations were found between VEB frequency greater than or equal to 20/hour and almost all VEB patterns for each follow-up; no significant associations were found between VEB prematurity (RR'/QT less than or equal to 1.00) and any of the VEB patterns. Among the survivors, the utilization of diuretics and beta blockers increased (p less than 0.01) and antiarrhythmic agents declined (p less than 0.01) between predischarge and all subsequent follow-up visits. The significance of these findings is discussed.

Adrenergic beta-Antagonists↗
PubMed1980

Method of reliable determination of minimal lethal antibiotic concentrations.

The lack of a standardized, statistically reliable method for in vitro determinations of the minimal lethal or bactericidal concentrations of antibiotics has complicated analyses of isolates of Staphylococcus aureus which appear to be inhibited but not killed by the usual concentrations of cell wall-active antibiotics. We describe a method which identifies some of the covariants involved in determinations of minimal lethal concentrations. Lethality was defined as a 99.9% reduction in the initial inoculum of bacteria after 24 h of incubation. We limited the sample volume to 0.01 ml to minimize the inhibitory effect of antibiotic and corresponding rejection values, which detected lethality with a high degree of sensitivity and specificity. When the number of colonies on subculture was equal to or less than the rejection value, the antibiotic was considered lethal for the test organism. Rejection values encompassed initial inocula from 10(5) to 10(7) colony-forming units per ml for single and duplicate samples and allowed for 1 or 5% variability in pipette volumes and errors in initial inoculum determinations. This method was used to determine the minimal lethal concentrations of semi-synthetic penicillins for S. aureau isolates, one of which was tolerant to the killing action of penicillin.

Anti-Bacterial Agents↗
PubMed1980

Test for 'miniature flies' following exposure of Drosophila melanogaster larvae to diagnostic levels of ultrasound.

An attempt has been made to replicate an experiment which reported the appearance of 'miniature flies' after exposure of Drosophila melanogster larvae to the field of a pulsed diagnostic ultrasound unit. No effects were observed with 1.5 mW temporal average acoustic power, the level of the original report. However, when temporal peak powers were increased by a factor of 10, approximately one fourth of the larvae failed to survive to the imago stage. No miniature flies were seen in the entire study.

Animals↗
PubMed1979

Ventricular ectopic beats and their relation to sudden and nonsudden cardiac death after myocardial infarction.

The role of ventricular ectopic beats (VEBs) in identifying patients who die of cardiac cause in the posthospital phase of myocardial infarction was evaluated in 940 patients who survived an acute coronary event. Six-hour Holter ECG recordings were obtained before hospital discharge, and VEBs were classified as complex (bigeminal, multiform, repetitive or R on T), simple (one or more VEBs that did not have complex patterns), or not present. Patients were followed 1-60 months (average 36 months) and cardiac mortality was categorized as sudden (less than or equal to 1 hour) or nonsudden (greater than 1 hour) among 98 witnessed cardiac deaths. Complex VEBs were associated with a significantly increased cardiac death rate, but did not discriminate between sudden and nonsudden death. Simple VEBs were associated with a 3-year cardiac mortality rate intermediate between those with complex and those with no VEBs. The relationship between complex VEBs and cardiac mortality was independent of 10 relevant clinical variables.

Aged↗
PubMed1977

Analgesic efficacy of an orally administered combination of pentazocine and aspirin. With observations on the use and statistical efficiency of GLOBAL subjective efficacy ratings.

The analgesic efficacy of a combination of pentazocine and aspirin (PA) in the ration 1:13 was compared with that of 650 mg of aspirin alone (A650) and with placebo (PBO), in 98 patients with postoperative pain. Two dose levels of the combination were compared: the lower dose (PA-L) consisted of pentazocine 25 mg and aspirin 325 mg, while the higher dose (PA-H) consisted of pentazocine 50 mg and aspirin 650 mg. All active treatments performed significantly better than PBO. PA-L performed as well as A650, while PA-H performed significantly better than A650. In addition to the usual subjective measures of analgesia, we obtained in 74 patients an evaluation of the overall (GLOBAL) performance of the treatment. This was rated on an ordinal scale of 1 ("poor") to 5 ("excellent"). On the GLOBAL scale, PBO had a mean score of 2.4 (fair-good); A650 and PA-L had scores of 3.6 and 3.9 respectively (good-very good): and PA-H had a score of 4.5 (very good-excellent). In five of six comparisons between treatment means, GLOBAL had the best discriminating power of all six measures. In the two comparisons of greatest interest (A650 against PBO and PA-H against A650), GLOBAL was more than twice as efficient as the TOTAL (summed pain score) measure. In comparing the statistical efficiency of different measures of the same analgesic effect, there is a problem in determining what are "clinically equivalent differences" on the various analgesic scales employed. We propose the use of the observed sample differences and the safeguard of repeating the comparisons over several studies to minimize the effect of random-origin bias.

Adult↗
PubMedDate not supplied

Transplant immunity in hamsters treated with ultrasound.

Hamsters with subcutaneous fibrosarcomas were treated by excision and by exposure to 5-MHz ultrasound for six minutes at an intensity of 3 W/sq cm. Rates for successful elimination of the tumors were between 80% and 90% and were not significantly different for the two methods of treatment. After 30 days, the animals were challenged with the same tumor cells. Animals successfully treated with ultrasound or excision required at least 10 times as many cells to produce a tumor as controls, indicating that eradication of the tumor by ultrasound induced a level of transplant immunity at least as good as that resulting from surgical excision.

Animals↗