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Biomedical subjects

J C Christensen

Publications and source records attributed to J C Christensen.

14 recordsLinked to original sources
PubMed1987

Exposure time and frequency of irradiation in brain tumours.

The survival of a group of patients with malignant gliomas of the brain submitted to radical surgery and radiotherapy was studied. The average survival was nearly 4 times longer with X-ray treatment than with cobalt 60 irradiation when a comparison was made between 24 patients with glioblasto-astroblastoma (grade 3-4) who received one or the other type of treatment (12 patients in each group). These results are ascribed to the fact that the daily exposures to X-ray were much longer than with cobalt and so, during those prolonged sessions, a greater number of tumour cells could be destroyed as they successively reached the pre-mitotic period of enhanced vulnerability to radiation. A smaller group of patients irradiated with linear accelerators fared worse than those who received X-ray treatment. Changes to the parameters of irradiation used at the present time with cobalt units or linear accelerators are suggested.

Astrocytoma↗
PubMed1986

Principles and descriptions of design of skin flaps for use on the lower extremity.

Distinction must be made between tissue movability and tissue elasticity when considering tissue movement with the hope of predicting good results. Tissue movability is either inherent, as on the back of the thigh, or is created by undermining, back-cutting, or cutting out Bürow's triangles. The elasticity of skin is inherent everywhere and is difficult to accurately predict. Elastic tissue will gape when cut, whereas inelastic tissue will not. Finally, elastic tissue will rotate with little puckering but inelastic tissue will form large dog-ears when rotated. For these reasons, as soon as the decision has been made to use a flap it is important to "prethink" the dynamics of flap movement and decide which type of flap to use and what is to be accomplished. If consideration is given to which flap will best allow proper transfer of tissue and at the same time give the best cosmetic result, the task is usually simpler. By further considering the secondary movement of surrounding tissues (as well as the primary movement), the number of potential techniques and designs are greatly increased.

Foot↗
PubMed1986

Flap classification and survival factors. Current concepts.

Flap survival variables are different for each type of flap and for each anatomic location. One must have sound knowledge concerning tissue survivability for all types of flaps. Otherwise, a high rate of failure may be experienced. A thorough knowledge of blood flow patterns of the foot and leg is paramount, as well as insight to the basic fundamental concepts concerning flap mechanics. These fundamentals include delay phenomenon, designing flaps, length-to-width ratios, and evaluation of flap vascularity. Successful and appropriate use of flaps in the lower extremity can be rewarding and provide the surgeon with a powerful tool to use in reconstructive procedures. Inappropriate or poorly performed flap procedures often create situations that are more difficult to manage than the original problem. According to Hoopes, "flaps are vicarious, mischievous, and frequently insubordinate reconstructive agents. They demand thorough understanding and meticulous attention for successful employment." Therefore, judicial use of these procedures is recommended.

Foot↗
PubMed1977

[Campimetric changes in optic radiation lesions].

Visual field defects may be congruous or not in lesions affecting the optic radiation. This fact, and the macular sparing found in some cases, can be explained if the optic radiation is envisaged as formed by three layers, the superficial corresponding to homolateral peripheral vision, the intermediate to contralateral peripheral vision, and the deepest to central vision from both hemimaculae. The fibers of all these layers fan out sequentially, first the more superficial, then the deeper, around the posterior part of the lateral ventricles, following a longitudinal plane of divergence in their way to area 17. The progressive displacement, upwards and downwards, of the thick fibers transmitting peripheral vision, leave out finally the thin fibers for central vision as the sole constituents of the central and terminal part of the optic radiation. As supporting evidence of this conception we have the fact that if the optic radiation is encroached on from its outer side (as it generally happens for reasons stated in the full text) visual field defects tend to be larger in the homolateral field. This holds true for temporal and parietal lesions, and to a lesser degree for occipital lesions. Deep lesions (for instance intraventricular tumours) tend to affect first the deeper strata of the optic radiation (macular vision and/or contralateral quadrants of peripheral vision). The schematic drawings presented allow us to understand how a temporal lesion may produce: a) no visual field defect, b) an upper homonimous quadrantopsia, c) a lower homonimous quandrantopsia, d) a homonimous hemianopsia; and that these field defects can be either congruent or uncongruous. Deep parietal lesions will produce visual field defects in the lower quadrants, which may be congrous or not. As the visual fibers for macular vision are deeply located in the optic radiation, forming a thin but wide layer in the vertical plane, they cannot be affected to a significative extent without the more superficial fibers for peripheral vision being also affected to an even greater extent. Due to the width and depth of this macular layer even in extensive lesions of the optic radiation some of its fibers can escape injury. This can explain macular sparing in some cases without resorting to hypothetical bilateral macular representation which is deemed unacceptable. Anatomical data and clinical examples are given which lend support to all these contentions.

Epilepsy↗
PubMed1976

After three years.

Explore the source record for details and available documents.

Education, Nursing↗
PubMed1975

Multiple sclerosis: some epidemiological clues to etiology.

The diagnosis of multiple sclerosis is frequently made with undue haste and without a firm basis. A false positive diagnosis is made in about 20 to 30% of the cases originally labeled as multiple sclerosis. The proportion of false positive diagnosis is probably still higher in countries where this disease is less frequent. An exhaustive investigation (neurological, clinical, neurorradiological, isotopic, etc.) is necessary before accepting such a diagnosis. This is particularly important because many of the lesions which can masquerade as multiple sclerosis are amenable to medical or surgical treatment. The prevalence of multiple sclerosis varies widely throughout the world, with a very definite preference for the white race. This difference seems to be caused, at least in part, by dietary habits. Lack of breastfeeding and excessive consumption of cow's milk during infancy is postulated as an important factor in the appearance of multiple sclerosis later in life. A lack of essential fatty acids (and may be of certain minerals and vitamins) in such a diet during pregnancy and childhood may result in the synthesis of abnormally unstable myelin. This underlying deficiency in myelin composition may be the substrate on which immunological factors act to produce the disease. The breakdown of this unstable myelin may be initiated by a variety of factors; natural decay of abnormally weak bonds in proteolipids, viral infection, immune reactions or even trauma. Immune reactions can explain, at least in part, the onset and the course of the disease, and probably immunodeficiency is the most important factor. Demyelination, once it starts, may continue until all abnormally formed myelin is destroyed, or until the building up of immunological defenses can stop the process. It follows from this that prevention of multiple sclerosis should be based mainly on dietic measures which ensure a sufficient supply of essential fatty acids, minerals and vitamins, during pregnancy and childhood. Breast feeding is probably the most important preventive factor. Skin pigmentation, either natural or from exposition to sunshine also seems to act as a preventive factor, and its mode of action deserves further investigation. Treatment of multiple sclerosis should be based on the improvement of immunological defenses, the elimination of possible allergens and saturated fats from the diet, and on the administration of sufficient amounts of essential fatty acids and of other various elements.

Adolescent↗
PubMedDate not supplied

Lateral ankle stabilization using bovine collagen material: xenograft bioprosthesis, model GR.

This is a combined research study including use of a reproducible technique for ankle stress x-ray examinations (both preoperatively and postoperatively) and the use of the bovine bioprosthesis tendon implant for stabilization and augmentation of the lateral ankle ligaments. The surgical technique is fully described and the follow-up results indicate that there is long-term ankle stability, and that patient acceptance is very high.

Adolescent↗