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Biomedical subjects

J Werner

Publications and source records attributed to J Werner.

At least 145 records · Page 8Linked to original sources
PubMed1989

Lumped versus distributed thermoregulatory control: results from a three-dimensional dynamic model.

In this study we use a three-dimensional model of the human thermal system, the spatial grid of which is 0.5 ... 1.0 cm. The model is based on well-known physical heat-transfer equations, and all parameters of the passive system have definite physical values. According to the number of substantially different areas and organs, 54 spatially different values are attributed to each physical parameter. Compatibility of simulation and experiment was achieved solely on the basis of physical considerations and physiological basic data. The equations were solved using a modification of the alternating direction implicit method. On the basis of this complex description of the passive system close to reality, various lumped and distributed parameter control equations were tested for control of metabolic heat production, blood flow and sweat production. The simplest control equations delivering results on closed-loop control compatible with experimental evidence were determined. It was concluded that it is essential to take into account the spatial distribution of heat production, blood flow and sweat production, and that at least for control of shivering, distributed controller gains different from the pattern of distribution of muscle tissue are required. For sweat production this is not so obvious, so that for simulation of sweating control after homogeneous heat load a lumped parameter control may be justified. Based on these conclusions three-dimensional temperature profiles for cold and heat load and the dynamics for changes of the environmental conditions were computed. In view of the exact simulation of the passive system and the compatibility with experimentally attainable variables there is good evidence that those values extrapolated by the simulation are adequately determined. The model may be used both for further analysis of the real thermoregulatory mechanisms and for special applications in environmental and clinical health care.

Body Temperature Regulation↗
PubMed1989

Closed loop control of human body temperature: results from a one-dimensional model.

A one-dimensional model of human thermo-regulation is used to solve a variety of basic problems in determining an adequate structure of the controller for metabolic heat production, skin blood flow and sweat production. Assuming one integrated central and one integrated peripheral afferent signal the controller parameters are evaluated by analysis of the control performance. Based on a validation by experimental results this allows the determination of a first optimized set of values for controller gains and weight of skin temperature feedback. Furthermore we analyse the effect of inhomogeneous distribution of heat production and blood flow, the influence of body fat content, of controller gains, of weight of skin temperature feedback and of depth of peripheral receptors on the dynamic performance. Increase of peripheral blood flow in particular evokes essentially both an increase of energy requirement in the cold and a quicker system response. Differing rates of increase of metabolic heat production are the consequence of differing body fat content. The weight of skin temperature feedback can be limited to 5...20%, because values outside this range evoke dynamic responses incompatible with the experiments. The actual value can only be determined if there is a correct assumption for the depth of the skin receptors. The use of measured superficial skin temperatures brings about an underestimation of the peripheral afferent signal. Of the controller gains it is primarily the gain of the metabolic controller which affects the dynamic response of the system. The experimental fact of a delayed onset of sweat production after a transition from cold to heat is the consequence of a high gain of the vasomotor system.

Adipose Tissue↗
PubMed1989

[Adequate measurement of artificial mineral fibers and evaluation of the biological effect].

Epidemiological and clinical medical examinations of exposed workers to man-made mineral fibers (MMF) to fix threshold limit values are presupposed by adequate measurements of MMF-dust. As yet are used technics which are unsatisfying. In consideration of the biological conditions in the breathing system a draft to measure MMF dust is introduced and proved. This draft based on the use of two-step-gravimetrical measurements together with membranous filter devices and evaluation by an electronic microscope.

Air Pollutants, Occupational↗
PubMed1989

Thermoregulatory models. Recent research, current applications and future development.

This review traces the efforts of different fields of thermoregulatory modeling. The aims of the three diverging branches can be characterized by (i) insight into functional physiological mechanisms and prediction of physiological phenomena, (ii) prediction of human performance for the protection of industrial workers or military personnel, and (iii) prediction of the impact of accidents, diseases, and clinical treatments. Common current and future efforts may be recognized which improve the physiological quality of the models for purposes either of physiological research itself or of promotion of the field of application, namely, (i) to approach the models to real geometry and anatomy of the human body, (ii) to simulate more adequately heat transport processes induced by the circulating blood, (iii) to implement more sophisticated regulatory concepts, (iv) to take into account interaction with other regulatory systems. "Environmental Ergonomics" should be an adequate forum for linking these diversified fields together.

Body Temperature Regulation↗
PubMed1988

Physical versus pharmacological counter-measures. Studies on febrile rabbits.

128 experiments were carried out on febrile rabbits at air temperatures of 8, 18, 24 and 30 degrees C in order to analyze the thermoregulatory effects and mechanisms of physical and/or pharmacological counter-measures. Fever was achieved by injection of 0.1 micrograms Salmonella typhi endotoxin (LPS)/kg into an ear vein. As the pharmacological counter-measure, injections of acetylsalicylic acid (ASA) into an ear vein were chosen. For the physical counter-measure, cooling thermodes (5 degrees C) were constructed for the abdominal skin, for the ear and for the rectum. ASA injections had no effect on the first fever maximum, even if applied 20 to 60 min before the LPS injection, but eliminated the second fever maximum. Of course, the additional hyperthermia observed at 30 degrees C ambient temperature could not be eliminated by the injections. On the other hand, cooling procedures can obviously not affect the pyrogen-induced temperature increase, but reduce the hyperthermic effect of a higher ambient temperature. Rectal cooling was more effective than ear or abdominal skin cooling. Abdominal cooling evoked an increase in metabolic heat production. Application of combined physical and pharmacological counter-measures achieved the strongest and quickest reduction of the second maximum, whereas the first maximum was not affected, as in all other experiments. The study emphasizes the necessity of taking into account the time course of the effector mechanisms in order to discriminate between hyperthermic and febrile components of temperature increase. In the initial phase cooling measures would evoke unwanted regulatory responses of the effectors, whereas during the second febrile maximum they would achieve a quicker reduction of core temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Temperature profiles with respect to inhomogeneity and geometry of the human body.

Temperature profiles within the human body are highly dependent on the geometry and inhomogeneity of the body. Physical parameters such as density and heat conductivity of the various tissues and variables such as blood flow and metabolic heat production of different organs are spatially distributed and thereby influence the temperature profiles within the human body. Actual physiological knowledge allows one to take into account up to 54 different spatially distributed values for each parameter. An adequate representation of the anatomy of the body requires a spatial three-dimensional grid of at least 0.5-1.0 cm. This is achieved by photogrammetric treatment of three-dimensional anatomic models of the human body. As a first essential result, the simulation system has produced a realistic picture of the topography of temperatures under neutral conditions. Compatibility of reality and simulation was achieved solely on the basis of physical considerations and physiological data base. Therefore the simulation is suited to the extrapolation of temperature profiles that cannot be obtained experimentally.

Body Constitution↗
PubMed1988

Intramedullary fixation of subtrochanteric fractures with the Williams Y-nail: report of three cases.

Küntscher Y-nailing is indicated for unstable proximal fractures of the femur in the elderly (5-7,10). The Williams modified Y-nail is an interlocking Y-nail that was designed to extend the indications beyond those of the Küntscher Y-nail. The Williams Y-nail was employed in three cases of subtrochanteric and subtrochanteric-intertrochanteric fractures, including one case in which there was an ipsilateral femoral shaft fracture. This procedure requires reaming and interlocking which are not performed in classic Küntscher Y-nailing. At follow-up (14-month minimum), each patient had a good clinical result and radiographic healing. Leg length shortening (maximum, 1.5 cm) occurred in two of three cases, primarily as a result of the failure to employ either a proximal or a distal interlocking screw. No other deformities have been observed. Williams Y-nailing can extend the indications of the Küntscher Y-nail to include rotationally unstable subtrochanteric fractures and associated ipsilateral femoral shaft fractures. The increased technical demands of the Williams modified Y-nail warrant cautious use depending upon the complexity of the fracture. Used properly, the Williams Y-nail may reduce the incidence of rotational and leg length deformities often experienced with other commonly used devices for unstable subtrochanteric and ipsilateral trochanteric-diaphyseal fractures of the femur.

Aged↗
PubMed1987

Control of sweating in man after work-induced thermal load and symmetrically applied cooling.

To examine the compensatory effects of work-induced thermal load and symmetrically applied local cooling on local sweat rates, two kinds of experiment were carried out on eight male subjects in a climatic chamber: 1) Experiments at 36 degrees C ambient temperature with a work load of about 25 W by the right leg. 2) Experiments at 36 degrees C ambient temperature with a work load of about 25 W by the right leg as in 1., but with additional compensatory cooling of the left leg controlled throughout by heat balance calculations at 75-85 W, equal to the heat produced in the working leg, the necessary air temperature being dependent on local sweat rate. Work load without cooling brought about a significant increase in core temperatures, metabolism, heart rate and local sweat rates. With unchanged local skin temperatures local sweat rate increase was higher in the working leg. Therefore the existence of muscle thermoreceptors should be assumed, the afferent information from which is processed and weighted in a different way to that provided by skin receptors. Work load combined with additional cooling reduced local and mean skin temperatures and heart rate, but had no significant influence on core temperature or metabolism. However, local sweat rate was generally lower in both thighs, with a major reduction in the cooled leg confirming control of local sweat rate by local temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiography↗
PubMed1987

Influences of overall thermal balance on local inputs for drive of evaporation in men.

Three kinds of experiments were carried out in a climatic chamber: experiments with warm load on the whole body at 36 degrees C (4 subjects); experiments at 36 degrees C with reduction of thermal load (28 degrees C) on the left leg (right leg at 36 degrees C) (8 subjects); and experiments at 36 degrees C with antisymmetric thermal load on the legs of 44 degrees C (right leg) and 28 degrees C (left leg), which resulted in additional thermal loads of +/- 30 W/leg (8 subjects). The additional thermal loads, which were applied via two climatic boxes, produced measurable effects on sweat rate when applied to one leg only. In comparison to the experiment 1, experiment 2 brought about a significant reduction of local evaporation on the left leg. With antisymmetric thermal loads on both legs (experiment 3), which did not influence the overall thermal balance, there was no significant influence on local evaporation, although significant changes of local temperatures were measured. It is suggested that the well-known regulatory models, declaring local, mean skin, and core temperatures as local evaporation drive should be supplemented with an important additional feature: local control of evaporation by local skin temperature may be blocked by an overall thermal balance.

Body Temperature Regulation↗
PubMed1987

Home health services in a climate of cost containment.

A survey of medicare certified agencies in the Northwest Region conducted to identify clinical problems of patients and families resulting from early discharge from hospitals revealed many concerns related to health care delivery. Major areas of concern were: Home Care and Community Services; Reimbursement and Funding; Rules and Regulations; Continuity of Care; Quality of Care; and Legal and Ethical Issues. Specific problems in each of the categories are discussed and strategies that home health agencies may utilize in addressing these areas are presented.

Aged↗
PubMed1986

Analysis of switching neurons within the thermoafferent system.

A total of 740 midbrain, thalamic, and hypothalamic neurons were tested as to their distribution and response/stimulus characteristics by means of thermal stimulation of the scrotal skin. The most frequent response type exhibited a basic discharge rate up to a threshold temperature and then switched to a maximum firing rate. The inverse behaviour was found in a low proportion. The temperature range in which the neurons switch from the 'low' to the 'high' state has been called the 'operating range' of the neuron. This study reveals, in contrast to former studies, that the 'operating range' is extremely narrow. This holds both for the individual neuron and for the populations studied. It is confirmed by simultaneous recordings and by cross correlation analysis that there is only one temperature threshold for all warm responsive neurons involved. It is concluded that according to the mean firing rate, temperature may only be discriminated as to below or above threshold. This means that a binary information is transmitted. For continuous temperature sensation and regulation either further neuronal types disposing of a continuous temperature/frequency characteristic or additional coding mechanisms have to be assumed. The major task of the switching neurons, integrating information from all over the body should be the generation of a trigger signal for warm defence.

Afferent Pathways↗