1. The variability of electrographic data used up to now is too large to discriminate easily between normal and abnormal. 2. This variability is partly caused by errors in the measuring process and its consequences. A sepcial difficulty is found in determining the beginning and the end of QRS, so that instantaneous vector magnitudes related to the starting or ending moment of QRS will have a high variance and therefore a low comparability. Displacements of the heart will play an important role as a source of errors. 3. It therefore seems to be more appropriate to describe structure and changes in time of the vector loop. To this end 3 new functions v, w and u are described, all three invariant towards positional changes of the heart in space. The term v means a time-dependent function describing the first derivative of the length of the instantaneous resulting vector of all electrical sources. The term w indicates the projection of the first derivative of the instantaneous vector into a plane orthogonal to the resulting vector. Therefore, v is dependent on the change of all resulting electrical forces, whereas w is the velocity of the peak of the resulting vector on its way along the vector loop. The interpretation of u is complicated; u is a measure of how much the vector leaves a plane, in which it normally more or less remains; u is therefore a measure for the edgeside view of the vector loop. 4 These data are combined with the well-known vectorial data to form a system of vectorial description. 5 The interpretability of these data in physiological terms is exemplified. The description presented here allows to go back to cardiac processes in the proper sense and to largely elimenate external influences like those of the thoracic shape on the ecg and vcg. 6. This way of describing an ecg is specially adapted to the discrimination of normal and abnormal in preventive tests.

Adult↗

PubMedDate not supplied

Skin pharmacokinetics.

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Administration, Cutaneous↗

PubMedDate not supplied

Bioequivalence of topical dermatological dosage forms--methods of evaluation of bioequivalence. AAPS/FDA Workshop on 'Bioequivalence of Topical Dermatological Dosage Forms-- Methods of Evaluating Bioequivalence', September 4-6, 1996, Bethesda, Md.

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Administration, Cutaneous↗

PubMedDate not supplied

Determination of the horny layer profile by tape stripping in combination with optical spectroscopy in the visible range as a prerequisite to quantify percutaneous absorption.

A new method was developed to determine the horny layer profile of volunteers using tape stripping in combination with UV/visible spectroscopy. The optical absorbance and the weight of corneocyte aggregates were compared as parameters for the determination of the mass of the horny layer particles fixed to the individual tapes. It was shown that the potential disturbances influencing both parameters must be considered critically before calculating the correlation factor, found as R2mean = 0.93 +/- 0.05. It was proven that the absorbance in the visible range is better suited than the weight to quantify the amount of corneocyte aggregates removed by a single strip. The new method allows an exact anatomical localization of the individual tapes and all data obtained within the depth profile of the stratum corneum. This was exemplified by the determination of the penetration of chemical and physical UV filters into the horny layer.

Adult↗

PubMedDate not supplied

Bioavailability of clobetasol propionate-quantification of drug concentrations in the stratum corneum by dermatopharmacokinetics using tape stripping.

The concentration of clobetasol propionate in the stratum corneum after application of three different formulations was determined, quantifying the influence of the formulations on the bioavailability of the drug. The stratum corneum was sampled by tape stripping. The concentrations of clobetasol propionate were determined quantitatively by HPLC. After application of Clobetasol Propionate Cream USP, 0.05%, and Temovate Cream, 0.05%, identical amounts of the drug were found in the stratum corneum, whereas after application of Temovate epsilon Emollient, 0.05%, the quantity was clearly decreased. From results obtained measuring the drug concentration in the adjacent sites of the skin where the creams had not been applied, it became clear that clobetasol propionate in Temovate epsilon Emollient, migrated to a large extent in the lateral direction. This explains the lower concentration measured for this formulation in the skin areas where the cream had been applied. In general, a lateral distribution of the applied drug must be taken into account when positioning the application areas on the forearm.

Administration, Cutaneous↗

PubMedDate not supplied

Percutaneous absorption of sunscreens in vitro: interspecies comparison, skin models and reproducibility aspects.

Appropriate evaluation of sunscreens is required to provide better knowledge of their safety and efficacy. One of the most important elements of this evaluation is the assessment of percutaneous absorption. In vitro methods are largely used for such assessments, and the accuracy of the measurements generated with these methods depends on the use of a proper methodology. This study was designed to evaluate an in vitro protocol for investigating the percutaneous absorption of two sunscreens under standardized experimental conditions. Octyl methoxycinnamate and benzophenone 4 were each incorporated in a typical oil-in-water emulsion and tested separately. Salicylic acid was tested as a reference compound. In vitro percutaneous absorption was evaluated using two species, the pig and human, and two models, full-thickness and split-thickness skin. The reproducibility of study results was evaluated by comparing the data generated by two industrial laboratories, L'Oréal and Hoffmann-La Roche. The correlation of quantitative data between pig skin and human skin was very good, and the split-thickness skin model seemed to be more appropriate for measuring the absorption of sunscreens. Results obtained for salicylic acid demonstrated the relevance of the protocol in terms of prediction of in vivo percutaneous absorption. Finally, the comparison of pig skin data between the two laboratories demonstrated a good correlation and underlined the need for a standardized in vitro procedure.

Animals↗

PubMedDate not supplied

The stripping technique: in vitro absorption and penetration of five UV filters on excised fresh human skin.

This article gives the results of a study whose aim was to compare the compartmental distribution and absorption of 5 UV filters, in vitro, by fresh human skin, after exposure times of 30 min and 16 h. These UV filters from BASF (octyl methoxycinnamate, benzophenone 4, benzophenone 3, octyl triazone and octocrylene) were incorporated separately in a simple oil-in-water emulsion. The composition of the emulsions was designed in order to obtain a sun protection factor of 5. Therefore the UV filters were introduced into the emulsions at different concentrations. We show that the affinity for each skin level [stratum corneum (SC), viable epidermis, dermis and receptor fluid] is different according to the test substance used. Some substances accumulated in the SC, whereas others passed through the skin very quickly and were quantified in the receptor fluid. The stripping technique allowed us to see that more than 94% of the chemical compound in the SC was in the first eight tapes. The problem of individual values below the limit of detection was raised, a correlation between the two exposure times was found (y = 1.702x - 0.105; R = 0.94) and a classification of products according to their affinity for the SC was determined.

Adult↗

PubMedDate not supplied

Penetration of titanium dioxide microparticles in a sunscreen formulation into the horny layer and the follicular orifice.

Coated titanium dioxide (TiO2) microparticles are commonly used as UV filter substances in commercial sunscreen products. The penetration of these microparticles into the horny layer and the orifice of the hair follicle was investigated. The distribution of the microparticles in the horny layer was analyzed using the method of tape stripping in combination with spectroscopic measurements. Deeper layers of the stratum corneum were devoid of TiO(2) even after repetitive application of sunscreen preparation when analyzing interfollicular areas. Only in the areas of the pilosebaceous orifices could microparticles be identified. The penetration of TiO(2) was investigated in histological skin sections. A biopsy was taken from a skin area from which the horny layer had been removed by tape stripping. In isolated areas, a penetration of coated TiO2 into the open part of the follicle was observed. The amount of TiO2 found in a given follicle was less than 1% of the applied total amount of sunscreens. A penetration of microparticles into viable skin tissue could not be detected.

Adult↗

PubMedDate not supplied

Penetration of vitamin A acid into human skin.

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1-Propanol↗