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Biomedical subjects

D Thomas

Publications and source records attributed to D Thomas.

At least 883 records · Page 49Linked to original sources
PubMed1982

Electrical excitability of artificial enzyme membranes. III. Hysteresis and oscillations observed with immobilized acetylcholinesterase membranes.

Experimental evidence for memory and oscillations in artificial acetylcholinesterase membranes is presented. When acetylcholine is injected on one side of an artificial proteinic membrane bearing acetylcholinesterase, a potential difference is recorded as a function of time. The steady-state potential due to the enzyme activity for increasing and decreasing substrate concentrations exhibits a hysteresis loop. The non-linearity of the enzyme reaction coupled with the diffusion constraints cause also some instabilities, such as oscillations of the membrane potential.

Acetylcholinesterase↗
PubMed1982

A quantitative method for the evaluation of spectral analysis patterns in carotid artery stenosis.

Duplex scanning in conjunction with Fast Fourier Transform Spectral Analysis offers a means of identifying stenotic internal carotid arteries, but few quantitative algorithms for interpretation of the spectral analysis patterns have been described. We first developed two objective parameters for analyzing carotid artery spectral analysis patterns which included a total of three peak frequencies in diastole and a ratio of spectral pattern areas between the internal and common carotid vessels. We then devised a formula for interpretation of the test results based on a computerized, best-fit, step-wise, discriminate analysis performed on 196 angiographically studied carotid vessels. This formula was then prospectively applied to 154 other carotid arteries with independently interpreted angiograms. 103/109 (94%) of the carotid arteries with less than 50% angiographic stenosis were correctly identified as were 40/50 (89%) of the vessels with 50% or more narrowing. Combining these groups with 16/17 (94%) properly classified total occlusions resulted in an overall accuracy rate of 93%. Application of the formula to smaller subgroups also showed significant differences in the formula means as they related to the degree of angiographic stenosis. Duplex scanning in conjunction with spectral analysis offers a reliable screening test for the evaluation of patients with suspected carotid artery stenosis.

Carotid Artery Diseases↗
PubMed1982

Regional distribution of steroids in the dog epididymis.

Concentrations of delta 4 androstenedione, testosterone and dihydrotestosterone were measured in the post-nuclear supernatant of the dog epididymis. In addition, they were measured in the efferent ducts and the testis. From the efferent ducts to the corpus there was a significant decrease in testosterone and delta 4 androstenedione concentrations. On the contrary, the concentration of dihydrotestosterone increased from the efferent ducts to the corpus where this steroid predominated. The marked differences in steroid concentration along the epididymis of the dog suggested regional differences in androgen metabolism.

Androgens↗
PubMed1982

Dural permeability to narcotics: in vitro determination and application to extradural administration.

The permeability of cranial and lumbar dura to various substances including a number of narcotic analgesics was measured in vitro. Preliminary data On human postmortem material is reported. Permeability had a linear relation to the inverse of the square root of molecular weight. This is the expected relationship for a diffusion process dependent upon molecular weight. The differential mass selectivity coefficients for lumbar and cranial dura were calculated; they were similar at 0.8 and 0.9. This was greater than for diffusion in simple liquids, but much less than that for biological lipid membranes. This suggests that the low rates of diffusion are a property of the thickness of the dura rather than any inherent impermeability. A simple model for the dural transfer of drugs is described, and applied to narcotics. Its purposes were to suggest: the factors involved in the dural transfer of drugs; the physicochemical properties of drugs relevant to their dural transfer; worthwhile measurements in future studies. The model indicates that drug molecular weight and rate of absorption are important determinants of the efficiency of dural transfer. Low molecular weight and slow absorption produce high dural transfers. When applied to narcotics, these factors could produce a difference of up to an order of magnitude in the amount transferred directly across the dura.

Absorption↗
PubMed1982

Acute i.v. Methadone Kinetics in Man: relationship to chronic studies.

Twenty-six patients were given methadone 10 mg i.v. to obtain acute human kinetics. Plasma methadone concentrations from separate 3- and 6-h studies were measured by radioimmunoassay. Kinetic parameters derived from triexponential NONLIN analysis showed that T1/2 alpha and T1/2 beta were 2 and 30 min respectively; no reliable estimate for T1/2 gamma could be obtained. The clearance was estimated as 149 /+- 62 and 163 /+- 49 ml min-1 in the 3- and 6-h studies respectively. These values are compared with those published for chronic administration. The difficulties in determining accurate terminal half-life and clearance values from short duration studies are discussed; these difficulties are accentuated by the long terminal half-life of methadone. Appropriate estimates of clearance may be derived from an acute short duration study provided that the average of triexponential fits to individual patients data is used, even when data extend from only 3h. As might be anticipated, no analysis produced appropriate terminal half-life values for this drug.

Adult↗
PubMed1982

Naproxen and diflunisal in osteoarthrosis.

Sixty-two patients with osteoarthrosis entered a 10-week double-blind cross-over trial of diflunisal and naproxen. Eight patients withdrew for drug-related reason, and seven for other reasons. There was no statistically significant difference in parameters of disease activity on each treatment period, but naproxen produced fewer withdrawals due to drug-related side-effects.

Aged↗
PubMed1982

Physician Sensitivity to the price of diagnostic tests: A U.S.-Canadian analysis.

A questionnaire containing 11 patient management problems was completed by 495 physicians and medical students at an American and a Canadian medical school. Respondents indicated whether they would order a particular diagnostic test in each case, given five different prices for the test. Approximately 25 per cent of attending staff and a higher proportion of residents, interns and clerks responded that they would order the test depending on its price. Approximately 50 per cent of attending staff and smaller proportions of residents, interns and clerks indicated that they would not order the test even if there were no price. Respondents in Montreal were more likely than those in Philadelphia to select a price-sensitive response, the reverse of the expected tendency. Since some tests may be ordered on the basis of price, education of physicians regarding the price of diagnostic test may alter their use of these services, but a large proportion of tests are ordered because of clinically absolute reasons, which may be insensitive to price.

Costs and Cost Analysis↗
PubMed1982

Immobilized thylakoids in a cross-linked albumin matrix: effects of cations studied by electron microscopy, fluorescence emission, photoacoustic spectroscopy, and kinetic measurements.

Immobilization of lettuce (Lactuca sativa) thylakoids has been performed by using glutaraldehyde and bovine serum albumin. Confirming previous reports, a stabilization of the O(2) evolution activity of the photosystem II (PSII) under storage and functional conditions has been observed. The present work is devoted to the role played by mono-and divalent cations, during the immobilization process itself, on the O(2) production. Four types of measurements have been employed: kinetic measurements, low temperature (77 K) fluorescence emission, photoacoustic (PA) spectroscopy, and electron microscopy observations. We show that the effect of glutaraldehyde is complex because it acts as an inhibitor, a stabilizing agent, and a cross-linking reactive. In the present studies, the thylakoids are immobilized within a polymeric insoluble albumin matrix. The highest activity yield and the best storage conditions are obtained when 0.15 mm Na(+) (or K(+)), 1 mm Mg(2+), and 0.1 mm Mn(2+) are present in the resuspending media before the immobilization. Due to modifications of the ionic content during such a process, structural differences are observed on the stacking degree of thylakoids. No modification of the fluorescence and PA spectra after the immobilization are found. Furthermore, a correlation between activities and spectral changes have been shown: when the activities increase, the F(735) to F(695) ratio increases and the PA(676) to PA(440) ratio decreases.

Journal Article↗
PubMed1982

Early detection of aortic dilatation in ankylosing spondylitis using echocardiography.

Aortic root abnormalities including cusp thickening, subvalvular stenosis, and mild aortic root dilatation are the most common cardiac complications in patients with long standing ankylosing spondylitis (AS). Twenty-three patients with definite idiopathic AS (New York Criteria 1966) and twenty-two matched controls were studied with M-mode echocardiography. Only one of the AS patients had clinical aortic incompetence. Six of the AS patients had mildly dilated aortic roots (normal less than 3.7 cm) with a mean diameter of 3.9 cm (range 3.8 to 4.00 cm). None of the twenty-two controls matched for age, sex and blood pressure had dilated aortic roots, with a mean diameter of 3.3 cm (range 2.9 to 3.6 cm). No correlation existed between aortic dilatation and severity of disease estimated by acute phase proteins--caerulo plasmin, alpha 1-antitrypsin, alpha 1 acid glycoprotein, ferritin and C Reactive protein. Contrary to a previous report, mild aortic root dilatation occurs in long standing cases of AS. Although it is a non-specific finding, it does not appear to be related to age or blood pressure and may therefore be the forerunner of aortic incompetence.

Adolescent↗
PubMed1982

Haematocrit, hypertension and smoking in patients with transient ischaemic attacks and in age and sex matched controls.

The blood pressure, smoking habit and haemotocrit of 154 patients with transient ischaemic attacks and 191 age-and sex-matched neurological controls were studied. Regression analysis revealed that the haematocrit value was related to both systolic and diastolic blood pressure, and to smoking. Smoking elevated the haematocrit by 1.9 +/- 0.59 in males and by 2.18 +/- 0.68 in females. When these associations were allowed for there was still evidence of a higher haematocrit in patients with transient ischaemic attacks (plus 1.44 +/- 0.56 in males and 0.75 +/- 0.75 in females p less than 0.02). The role of an elevated haematocrit in the pathogenesis of cerebrovascular disease and its management are briefly discussed.

Adult↗
PubMed1982

The effect of aminophylline on inspiratory muscle contractility.

The effects of aminophylline on diaphragmatic muscle contractility were studied in 8 dogs. The relationships of the electromyographic signal from the diaphragm and the pressures developed by this muscle were compared before and after the administration of aminophylline in doses of 6, 20, 40, 80, and 120 mg/kg. Measurements were made during occluded inspiratory efforts at functional residual capacity. In a second group of 4 dogs the relationships were compared while the rib cage expansion was limited by a plaster cast. Finally, in a third group of 4 dogs after the diaphragm had been paralyzed by phrenicotomy, the relationship of pleural pressure to the electromyographic signal of the intercostal muscles was assessed before and after administration of aminophylline. In all cases, aminophylline progressively shifted the electromyographic pressure relationship up and to the left. This effect became significant (p less than 0.01) at a dose of 20 mg/kg, reached a peak at 80 mg/kg, and then declined at a dose of 120 mg/kg. The amount producing blood concentrations closest to the human therapeutic blood concentration was 20 mg/kg. The peak increase in pressure compared with the control values were 58% in the first group, 27% in the second group, and 52% in the third group (p less than 0.01). We conclude that aminophylline increases respiratory muscle contractility in a dose-related manner. This may have important therapeutic and pathophysiologic implications.

Aminophylline↗
PubMed1982

Objective criteria for the interpretation of carotid artery spectral analysis patterns.

The duplex scanner (imager + pulsed Doppler) in combination with a fast Fourier transform spectrum analyzer has been used to identify areas of arterial narrowing. To evaluate its effectiveness in the detection of clinically significant carotid stenosis, 1 previously described and 2 original objective parameters were applied to the real time sound frequency tracings from 157 carotid arteries that also had angiograms available to determine the presence and degree of stenotic involvement. There was a statistically significant difference between the means of the test scores of the group of vessels with high grade narrowing (greater than or equal to 60%) and those with less than 40% stenosis for all 3 criteria. Of major clinical interest were our 2 parameters, the 3-point diastolic internal carotid frequency total and the internal-to-common carotid spectral area ratio, both of which showed considerable promise as predictors of stenotic disease. For each test, 40/46 (87%) of the test scores of the arteries with 50% or greater narrowing fell outside 2 standard deviations (95% confidence level) of the means of the vessels with less than 50% stenosis. A previously reported parameter, the internal-to-common carotid peak systolic frequency ratio, was notably less discriminant in this regard.

Arterial Occlusive Diseases↗
PubMed1982

[Treatment of peritonitis in continuous ambulatory peritoneal dialysis ].

UNLABELLED: Thirty patients were treated with continuous ambulatory peritoneal dialysis during 313 patients months. 26 episodes of peritonitis defined by a cloudy dialysate with more than 100 cells/mm1 and more than 50 p. cent of polynuclear were observed. The organisms initially responsible were Gram-positive in 11 cases (6 Staphylococcus aureus, 1 Staphylococcus albus, 4 Streptococcus viridans), a gram negative in 3 cases (1 Klebsiella, 1 serratio, one unidentified), a Candida in 2 cases. In 10 cases, the culture was negative, Initial treatment was peritoneal lavage (40 l/day) with in situ antibiotics: in the absence of Candida, the association sulfamethoxazole (SMZ) (80 mg/l) and trimethoprim (TMP) (16 mg/l) was used; when Candida was present amphotericin B (5 mg/l) was used. The association SMZ + TMP led to cure of PT in 17 cases, in 7 +/- 4 days. In 5 cases, this initial treatment was changed at the 48th hour because of initial resistance in one case or secondary resistance of Candida surinfection (2 cases). Candida surinfection occurred later in 2 other cases. For these 6 primary or secondary Candida peritonitis, the catheter was changed within 48 hours. Nevertheless, death occurred in 3 cases and cure was obtained after 51 +/- 11 days in the 3 other cases. CONCLUSIONS: 1) The initial treatment by SMZ + TMP appears quite effective in most cases (73%). 2) The severity and the high incidence of Candida surinfection suggest that its systematic prophylaxis may be appropriate.

Adult↗
PubMed1982

Clinical and metabolic abnormalities associated with occupational exposure to polychlorinated biphenyls (PCBs).

A cross-sectional study of 120 male workers was conducted to determine the prevalence of increased polychlorinated biphenyl (PCB) absorption as well as the presence of potentially related clinical and metabolic abnormalities. Three exposure categories ("exposed", "nominally exposed", "nonexposed") were defined. Complete work histories, clinical histories, physical examinations and laboratory tests, including plasma PCB determinations were obtained. In addition, fat PCB levels were determined in randomly selected subjects in each exposed group. Evidence of dermatotoxicity was observed and elevated PCB levels were noted more frequently in the exposed group (p less than .0001), correlating well with age and duration of employment. These correlations were stronger for fat (p less than .001) than for plasma (p less than .01) PCB levels. In the exposed group, significant correlations were found between plasma PCB and serum triglyceride (p less than .0001) and serum glutamic oxaloacetic transaminase (SGOT) levels (p less than .01). These correlations remained significant after controlling for either age or length of employment. No significant correlations were found between PCB levels and levels of cholesterol, high-density lipoprotein cholesterol or levels studied on liver function tests other than SGOT. Further analyses relating frequency of reported direct contact with PCB levels suggested a dermal route of exposure. An analysis by union affiliation demonstrated that those in crafts involving greater direct exposure had correspondingly higher elevations of PCB levels.

Adolescent↗