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Biomedical subjects

A Venot

Publications and source records attributed to A Venot.

54 records · Page 3Linked to original sources
PubMed1987

Structural identifiability of "first-pass" models.

This paper considers the structural identifiability of two compartmental models classically used to describe the pharmacokinetics of drugs orally administered and transformed into a metabolite with a first-pass effect at the hepatic level. The simplest model proves not to be globally identifiable even when plasma and urinary measurements of the drug and metabolite concentrations are made. It admits two sets of admissible solutions, so that a priori knowledge must be introduced to distinguish them. The more complex model appears globally identifiable when blood and urine measurements are made.

Humans↗
PubMed1986

Nifedipine and thallium-201 myocardial perfusion in progressive systemic sclerosis.

Heart disease in patients with progressive systemic sclerosis may be due in part to myocardial ischemia caused by a disturbance of the coronary microcirculation. To determine whether abnormalities of myocardial perfusion in this disorder are potentially reversible, we evaluated the effect of the coronary vasodilator nifedipine on myocardial perfusion assessed by thallium-201 scanning in 20 patients. Thallium-201 single-photon-emission computerized tomography was performed under control conditions and 90 minutes after 20 mg of oral nifedipine. The mean (+/- SD) number of left ventricular segments with perfusion defects decreased from 5.3 +/- 2.0 to 3.3 +/- 2.2 after nifedipine (P = 0.0003). Perfusion abnormalities were quantified by a perfusion score (0 to 2.0) assigned to each left ventricular segment and by a global perfusion score (0 to 18) for the entire left ventricle. The mean perfusion score in segments with resting defects increased from 0.97 +/- 0.24 to 1.26 +/- 0.44 after nifedipine (P less than 0.00001). The mean global perfusion score increased from 11.2 +/- 1.7 to 12.8 +/- 2.4 after nifedipine (P = 0.003). The global perfusion score increased by at least 2.0 in 10 patients and decreased by at least 2.0 in only 1. These observations reveal short-term improvement in thallium-201 myocardial perfusion with nifedipine in patients with progressive systemic sclerosis. The results are consistent with a potentially reversible abnormality of coronary vasomotion in this disorder, but the long-term therapeutic effects of nifedipine remain to be determined.

Adult↗
PubMed1986

Pharmacodynamic effect of dipyridamole on thallium-201 myocardial perfusion in progressive systemic sclerosis with diffuse scleroderma.

We evaluated the effect of dipyridamole on thallium-201 myocardial perfusion in 23 patients with progressive systemic sclerosis (PSS) with diffuse scleroderma. Thallium-201 single photon emission computed tomography (SPECT) was performed at rest and after coronary artery vasodilatation with intravenous dipyridamole (0.14 mg/kg/min for four minutes). The left myocardium was divided into nine segments; each segment was graded as 2.0, 1.5, 1.0, 0.5, 0 (zero represents no activity). Dipyridamole significantly improved resting thallium-201 myocardial perfusion: the mean (SD) number of segments with thallium defects decreased from 6.0 (2.1) at rest to 4.1 (2.5) after dipyridamole (p less than 0.0001); the mean (SD) score in segments with resting defects increased from 0.92 (0.24) at rest to 1.13 (0.38) after dipyridamole (p less than 0.0001); the mean (SD) global score per patient increased from 10.2 (1.8) at rest to 11.4 (2.1) after dipyridamole (p less than 0.02); the global score increased by at least 2.0 in 12 patients and worsened by at least 2.0 in three patients only (p = 0.05). The results of this acute study suggest that some drugs with potent vasodilator activity on small coronary arteries may be beneficial in the treatment of PSS patients with thallium-201 myocardial perfusion abnormalities.

Adult↗
PubMed1986

Automated comparison of scintigraphic images.

New algorithms for automated comparison of scintigraphic images have been developed and are described here. The first step presented here is the registration of the images, performed by optimizing, with respect to the registration parameters (two translational shifts, one angle of rotation, the two parameters of a linear transformation of the gray levels), the stochastic sign change (SSC) criterion. The optimization of this criterion is demonstrated to be efficiently performed using the adaptative random search strategy; a more limited but less time-consuming method is also presented. The second step described is the point-by-point comparison of the registered images. The pixel-by-pixel application of Poisson variable statistical tests permits the generation of the significant image differences. From such images it is possible to detect modifications which escape visual inspection. Examples of applications are given in controlled and routine conditions. These algorithms are useful for the processing of many investigations and are proposed for implementation on all nuclear medicine data processing systems.

Bone and Bones↗
PubMed1985

Cytoplasmic and nuclear uptake of aldosterone in toad bladder: a mathematical modeling approach.

The mechanism of aldosterone uptake in the epithelial cells of toad bladder was studied using mathematical modeling. Two complementary approaches were used. The first involved analysis of cytosolic aldosterone binding at steady state according to models defined by the sum of independent noninteractive binding sites. The best model describing the experimental data corresponded to two specific binding sites with mean dissociation constant values of 0.20 and 60 nM for types 1 and 2, respectively. The second approach was based on the analysis of cytoplasmic and nuclear aldosterone uptake kinetics at 25 and 0 degrees C in intact bladder. Two models (A and B) were studied. They both implied the existence of two types of aldosterone binding sites as precursors of the corresponding chromatin bound complexes. In model A, nuclear translocation of the two types of receptors was assumed to obey first-order kinetics. In model B, the translocation process for type 1 sites involved a time lag leading to delayed binding to chromatin. Both models were found to fit the experimental data satisfactorily. The fit obtained for model B appeared to be better at low aldosterone concentrations.

Aldosterone↗
PubMed1985

[Computerized comparison of imaging in scintigraphy; physiopathological applications].

The authors describe a method of treating scintigraphic data with which they can correctly compare images of a structure that were obtained in different conditions. This method comprises two steps which are fully computerized. During the first one known as the "registration" step and intended to make a comparison possible they maximise a new similarity criterion by a series of random trials in a five parameter space. During the second, which is the actual comparison, they use an appropriate statistical test to recognise those homologous pixels with a significantly different contents which will be the only ones retained to build up the final image. They give then two examples of what the method brings in the medical field which are the detection of adenomatous parathyroid glands and the follow-up of lung perfusion in case of embolism.

Adenoma↗
PubMed1984

Reversible hydronephrosis in the rat: a new surgical technique assessed by radioisotopic measurements.

A new technique for experimental reversible hydronephrosis in the rat was developed. A noninvasive radioisotopic investigation, using Tc-99m dimercaptosuccinic acid, permitted sequential assessment of the separate renal function at different stages of the study. After 1 week of unilateral ureteral obstruction, reversibility was obtained by the removal of the obstructive device. Ten days after the obstruction release, the ipsilateral kidney had returned to 71 per cent of its preligation uptake value. Histological findings demonstrated the reversibility of the surgical obstruction.

Animals↗
PubMed1983

An automated method for the normalization of scintigraphic images.

The computer comparison of two images of the same organ requires normalization of the images. We propose an iterative, automated method of normalization that is highly insensitive to structural modifications in the images. The normalization factor is calculated by maximizing the number of sign changes in the scanned subtraction image with a unidimensionnal optimization method. This algorithm is efficient, computationally cheap, and can be implemented on most nuclear medicine data-processing systems.

Computers↗
PubMed1979

A non-linear mathematical model for the in vivo determination of Kupffer cells number and rate of phagocytosis of radiocolloids in rats.

In order to perform a quantification of the hepatic RES function, a mathematical model of the colloids phagocytosis was constructed and validated in normal and partially hepatectomised rats. The experimental design consisted of the collection of successive blood samples for the measurement of radiocolloids time courses after the injection of different doses of gelatin colloids (0.075--5 mg of gelatin/100 g body wt). The unknown parameters were estimated by method of maximum likelihood using a second order algorithm. A good fit between experimental and simulated data was obtained for a large range of injected doses using a single set of parameters. Comparisons of parameters values between normal and hepatectomised rats were found to be -onsistent with the hepatectomy ratio. This computerised estimation of parameters provides a determination of both the total number of Kupffer cells and the mean time of a complete phagocytosis cycle which cannot be obtained by classical approaches.

Animals↗
PubMedDate not supplied

Best mode of expression of acute reversibility of airway obstruction in patients with asthma: application to a new beta-2 agonist, RU 42 173.

Lung function tests must distinguish a true drug-induced bronchial response from changes not related to the drug itself, mainly due to intra-individual variability. We compared the variability and ability to detect true drug-induced bronchodilation of 3 modes of expression of the increase in forced expiratory volume in 1 second (delta FEV1) following administration of a 0.25 mg single oral dose of RU 42 173, a new beta 2-agonist. The study was performed in 12 patients with reversible obstructive asthma in a double-blind, crossover, placebo-controlled, randomized manner. The variability of each index was assessed by calculating the coefficient of variation (SD/mean). True drug-induced bronchodilation was assessed by calculating the F value of each index corresponding to the ratio of between-treatment to within-group differences. Three modes of expression of delta FEV1 were compared: delta FEV1 (L) = the absolute increase in FEV1, delta FEV1 (% baseline) and delta FEV1 (% predicted) where delta FEV1 (L) is divided by baseline FEV1 or predicted FEV1, respectively. A statistically significant increase in FEV1 was found up to respectively 3, 2 and 4 hours after dosing when using delta FEV1 (L), delta FEV1 (% baseline) and delta FEV1 (% predicted). The highest F value was obtained for delta FEV1 (% predicted). The coefficient of variation was lower with delta FEV1 (% predicted) than delta FEV1 (L) and delta FEV1 (% baseline). In conclusion, RU 42 173 showed a bronchodilating effect which appears to be clinically relevant. delta FEV1 (% predicted) was to be the least variable and most powerful index and should be preferred to delta FEV1 (L) and even more to delta FEV1 (% baseline) to assess the acute airway response to a bronchodilator drug.

Adrenergic beta-Agonists↗