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PubMed1979

[Stereoscopic photography in plastic surgery (author's transl)].

A major problem in reconstructive and plastic surgery of the face is the assessment of exact distances between certain points of reference across facial contours. Incorrect estimation of these variables produces unsatisfactory postoperative anatomical results. Therefore a method, which permits exact measurements using stereoscopic photography of models, was tested. On the models quantitative studies of the effects of surgical techniques were made. Facial asymmetry and various phases of facial animation can be assessed and documented, and the progress of expanding tumours can likewise be followed.

Adult↗
PubMed1979

Parenchymal mechanics at the alveolar level.

Three current questions about alveolar mechanics are discussed: how is the liquid lining of the alveolus maintained, how does surface tension affect alveolar geometry and lung recoil, and how does the parenchyma respond to nonuniform deformations? Modeling the parenchyma as an interconnected network of alveolar walls is emphasized and modifications that are needed to make the models quantitatively successful are suggested.--Wilson, T. A. Parenchymal mechanics at the alveolar level.

Animals↗
PubMed1983

Enhancing managerial effectiveness in dietetics.

Environmental pressures from such sources as economic conditions, the government, third-party payers, and inter-institutional competition create managerial challenges. Although cost-containment has received considerable attention, long-term cost-effectiveness is probably the significant issue. Dietitians must become more cost-conscious and effective in resource management to attain desired performance outcomes. Some of the skills and characteristics essential to managerial effectiveness are a marketing orientation, systems design skill, quantitative operations management techniques, financial expertise, and leadership. These abilities facilitate decision-making and achievement of long-term cost-effectiveness. Curriculum enhancement and continuing education are two strategies for improving managerial competency in the dietetics profession. In dietetics education, study of management topics should be enhanced to provide more advanced coverage of management theories and quantitative models so that managerial performance can be at a higher level of sophistication and competency. To assure the viability of the dietetics profession, the emphasis on management must be more comprehensive and rigorous.

Cost-Benefit Analysis↗
PubMed1984

Children's perception of visual and auditory speech.

Preschool children's evaluation and integration of visual and auditory information in speech perception was compared with that of adults. Subjects identified speech events, which consisted of synthetic speech syllables ranging from /ba/ to /da/ combined with a videotaped /ba/, /da/, or no articulation. Both variables influenced the identification judgments for both groups of subjects. The results were used to test current views of the development of perceptual categorization and speech perception. Tests of quantitative models indicated that both preschool children and adults had available continuous and independent sources of information. The results were well described by a fuzzy logical model of perception, which assumes that the perceiver integrates continuous and independent sources of information and determines the relative goodness of match to prototype definitions in memory. The only developmental difference was less of an influence of the visual source of information for children relative to adults. 1 explanation is that the children simply attended less to the visual source. A second experiment eliminated the attentional explanation by showing identical results when the children were also required to indicate whether or not the speaker's mouth was moving.

Adolescent↗
PubMed1983

Analysis of the microphonic potential of the bullfrog's sacculus.

The sensory epithelium from the bullfrog's sacculus was mounted between two chambers and stimulated by moving the otolithic membrane with a piezoelectric stimulator. The evoked response was measured as the transepithelial "microphonic" potential or, when the epithelium was voltage clamped, as the microphonic current. Microphonic responses were similar to those recorded in other preparations: the whole organ produced a "2f" response (i.e., a response of a frequency twice that of the stimulus) which could be changed to a single-polarity response by stimulating cells of a single polarity; the response saturated asymmetrically with displacement, producing a rectification; and the amplitude declined at high and low frequencies. To determine the cellular elements responsible for generation of the microphonic potential, the equivalent circuit of the epithelium was estimated from morphological and electrophysiological data, and responses to step displacement stimuli were recorded. Four elements in particular shape the microphonic potential: the complex impedance of the extracellular current path, the saturating displacement-conductance curve, an adaptation mechanism which shifts that curve, and a voltage-dependent K+ conductance in the basolateral hair cell membrane. A quantitative model incorporating these elements accurately reproduces the observed responses.

Acoustic Stimulation↗
PubMed1984

Can physicians be rational about diagnostic tests?

Concerns about diagnostic test utilization have led to interest in the role of tests in clinical decision-making, and researchers have developed guidelines for interpreting the results of diagnostic tests using Bayesian probability revision and decision analysis. Although it acknowledges the importance of these quantitative models in medical education, this article identifies major obstacles that limit their application, demonstrating that " rational " decision-making may not be rational or optimal in clinical practice.

Clinical Laboratory Techniques↗
PubMed1980

Morphometry of human leukocytes.

In order to establish quantitative models of leukocyte functions, several morphometric parameters on individual white cells are needed. These include the diameter, volume, and membrane area of the cells and their nuclei in the undeformed state. A stereologic method was used to obtain these quantities from transmission electron microscopy of random sections through human white blood cells (neutrophils, lymphocytes, monocytes, and eosinophils). In order to estimate possible artifacts due to preparation of the cells for transmission electron microscopy, a detailed comparison with light microscopy was made. The results show that undeformed white cells in isotonic solution are spherical with many membrane foldings and have a significantly smaller diameter than that measured on blood smears. A method of chemical fixation was employed so that the shrinkage due to fixation of the cells is below the resolution of light microscopic measurements. Further, it was shown that all leukocytes, including lymphocytes, have much more membrane area than is needed to cover their volumes, and this membrane area remains constant when the cell is hypotonically swollen.

Adult↗
PubMed1980

The rickettsial plaque. Evidence for direct cytopathic effect of Rickettsia rickettsii.

Monolayers of primary chick embryo cells were infected with Rickettsia rickettsii in a plaque assay system with 0.5 per cent agarose overlay. Plaques appeared 5 days after inoculation and were examined on day 6 by supravital staining, immunofluorescence for R. rickettsii, and electron microscopy. In all studies maintenance of the topographic integrity of the monolayer and the plaque allowed assessment of temporospatial relationships of rickettsial infection and cytopathologic changes. Plaques comprised four zones: peripheral, marginal, necrotic, and central. The cells of the peripheral zone were viable, mildly infected, and ultrastructurally normal. Cells of the marginal necrotic, and central zones exhibited a correlation between quantity of rickettsiae and presence of cytopathology. Pathologic changes included sever dilation of rough endoplasmic reticulum and necrosis. Quantitative assessment of the distribution of rickettsiae ultrastructurally showed the overwhelming predominance of cytosol location and suggested the ultrastructural sequence of events for rickettsial release from cells via lysis of cell membrane at the end of filopodia. These studies of the plaque technic provide a predictable, quantitative model for experimental investigations into mechanisms of cell injury by rickettsiae.

Animals↗
PubMed1983

Selective adjustment of the speed of internal clock and memory processes.

Four experiments studied the scaling of time by rats. The purpose was to determine if internal clock and memory processes could be selectively adjusted by pharmacological manipulations. All of the experiments used a temporal discrimination procedure in which one response ("short") was reinforced following a 2-sec noise signal and a different response ("long") was reinforced following an 8-sec noise signal; unreinforced signals of intermediate duration were also presented. The proportion of "long" responses increased as a function of signal duration. All drugs were administered intraperitoneally (ip) and their effect on clock or memory processes was inferred from the observed pattern of change in the point of subjective equality of the psychophysical functions under training and testing conditions. Experiment 1 demonstrated that methamphetamine (1.5 mg/kg) can selectively increase clock speed and that haloperidol (.12 mg/kg) can selectively decrease clock speed. Experiment 2 demonstrated that footshock stress (.2 mA) can selectively increase clock speed during continuous administration but leads to a decrease in clock speed below control values when the footshock is abruptly terminated. Experiment 3 demonstrated that vasopressin (.07 pressor units/kg) and oxytocin (.02 pressor units/kg) can selectively decrease the remembered durations of reinforced times, which suggests that memory storage speed increased. Experiment 4 demonstrated that physostigmine (.01 mg/kg) can selectively decrease the remembered durations of reinforced times and that atropine (.05 mg/kg) can selectively increase these remembered durations, which suggests that memory storage speed was differentially affected. The conclusion is that internal clock and memory processes can be dissociated by selectively adjusting their speed of operation and that these changes can be quantitatively modeled by a scalar timing theory.

Animals↗
PubMed1982

[Origin and evolution of the genetic code].

We propose a quantitative model which suggests that the present genetic code appeared under the influence of mutations, while optimizing its own resistance against their effects. Its evolution was realized by successive steps in which the number of translated codons grew, whereas the number of terminators decreased. The main constraint of this model is selection against nonsense mutations: the competition among many primitive codes gives advantage to those which resist best to the occurrence of nonsense mutations. The structures of the selected systems converge towards that of the present genetic code. This one appears then as built so as to resist to errors, information noise, mutations.

Biological Evolution↗
PubMed1980

The origin of the T-wave.

Of all the features of the electrocardiogram, the T wave shows the earliest and most dramatic correlation with abnormalities of electrical behavior in the heart. Yet, it has remained difficult to make quantitative connections between the T wave and electrical activity in the heart at the cellular level. It is the purpose of this paper to review attempts at deriving T waves from a knowledge of the membrane electrical activity in the heart and the geometry and conductive properties of the heart and its surrounding medium. We first summarize the problem of calculating T-wave potentials on the body surface, based on physical laws. Next, we review the empirical conclusions that have been reached through observations of the T wave, including its connection with repolarization of the cell membrane, the distributed nature of the current source during the T wave, and the gradient in action potential duration responsible for the positive polarity of the normal T wave. Six quantitative models have been proposed for the T wave; we compare these models and comment on their accuracy and underlying assumptions. Finally, we discuss ideas that have been suggested for the membrane mechanism of repolarization and the T wave.

Action Potentials↗
PubMed1981

Protective effect of hydroxyzine and phenylpropanolamine in the challenged allergic nose.

Allergic rhinitis patients were challenged with intranasal allergen aerosols after pretreatment with hydroxyzine and phenylpropanolamine, singly and in combination. Hydroxyzine protected against itching, sneezing and hypersecretion but aggravated obstruction. Phenylpropanolamine had a subtle but measurable anti-congestive effect. This model quantitates and confirms the complementary effects of combined antihistamine-decongestant therapy.

Adult↗
PubMed1980

Visual consequences of the foveal pit.

When viewing a uniform field through a small aperture moved circularly before the pupil of the eye, many observers report a diffuse dim spot subtending roughly 1 degree visual angle, which rolls around the fixation point in synchrony with the motion of the aperture. Measurements of the Stiles-Crawford maximum for different locations within the fovea confirm that small but systematic shifts in foveal directional sensitivity are responsible for this entoptic effect. A quantitative model is developed which accounts for the directional sensitivity shifts on the basis of refraction of light at the sloping sides of the foveal pit. Supporting evidence for the model is provided by a second entoptic phenomenon: fundal scatter from the image of a glare source on the eccentric retina is reflected by the foveal pit in such a way as to render it visible. Estimates of the slope of the foveal pit from this effect agree well with that predicted from the observed shifts in directional sensitivity.

Fixation, Ocular↗
PubMed1995

[The calculation of AIDS costs in Spain by simulation technics].

BACKGROUND: The aim of this study was to elaborate a quantitative model integrating the clinical, and epidemiologic characteristics of the economic costs of the treatment of HIV infected and AIDS patients in Spain to determine the future evolution of the treatment of HIV infected and AIDS patients in Spain to determine the future evolution of the disease and predict the costs of the treatments for the Spanish health care system in 1995. METHODS: A model based on the calculation of probabilities in which the classification of AIDS patients was designed in three phases: early, intermediate and AIDS and established the relations of changes among the phases and included the economic costs of each of the treatments. The model was programmed on a calculation sheet to allow possibilities of disease evolution to be configured in addition to the costs. RESULTS: In 1995 the health care system will treat 22,000 AIDS patients together with those with HIV infection leading to three million hospital stays, equivalent to 8,000 hospital beds dedicated to each treatments with a budget repercussion of close to 90,000 million pesetas. The number of consultations to specialists will increase to up to 570,000 with the total cost of health care treatments being up to 113,000 million pesetas. CONCLUSIONS: The results of this model indicate high health care costs derived from the treatment of AIDS and HIV infection. Given the fact that it is possible to perform simulations with the model under other hypothesis, basic clinical, epidemiologic and economic data are required to determine the most realistic possibilities to thereby orient global policies concerning this disease.

Acquired Immunodeficiency Syndrome↗
PubMed1975

[Proliferation kinetics of bile duct epithelia in the regenerating mouse liver after CCl4-poisoning].

Autoradiographic and morphometric methods were used in studying the proliferation of interlobular bile duct epithelia of adult NMRI mice after CC14-poisoning (1 ml/kg i.p.). DNA synthesis starts on the 2nd day after CC14 administration. The time course of the 3H-thymidine labelling index is biphasic, with a first maximum at 2.5 and a second one 5 days after CC14 injection. An S-phase of 5.8 h was measured by 3H plus 14C-TdR double-labelling experiments. Proliferation is completed 10 days after CC14-poisoning, coinciding with the restitution of the liver parenchyma. Bile-duct epithelia remain diploid during the whole proliferative period, which suggests that every S-phase leads to mitotic division. The number of duct cells in portal cross sections remains constant. A quantitative model of the CC14- induced proliferation of interlobular bile duct cells is presented after calculating the total number of S-phases, the increase in cell number, and the final percentage of 3H-labelled nuclei (continuous infusion of 3H-TdR) as a function of time: With regard to 100 bile duct cells at the onset of proliferation 20 per cent S-phases occur during the first maximum and an additional 26 per cent occur during the second maximum of DNA SYNTHESIS, WHICH LEADS TO A 1.46-FOLD INCREASE IN CELL NUMBER. As derived from continuous 3H-TdR labelling (48 per cent 3H-labelled nuclei at the 6th day) and autoradiographic grain density measurements, the second wave of S-phases is due to DNA synthesis in ductular cells that have been formed during the first proliferative maximum. It is not possible to determine whether the proliferative activity observed is induced by lethal damage to bile-duct cells in the early course of CC14-poisoning, followed by compensatory growth and replacement of degenerate cells, or by nonspecific growth stimulation, inducing hyperplastic growth and elongation of terminal bile ducts.

Animals↗
PubMed1994

Beyond dummy variables and sample selection: what health services researchers ought to know about race as a variable.

OBJECTIVE: This article addresses the definitional and methodological problems associated with the most common uses of race as a variable in health research. PRINCIPAL FINDINGS: Although often used in health services research, race is a poorly understood concept because it lacks conceptual clarity. Moreover, the measurement problems with race have not yet been adequately addressed. As a result, many quantitative models that attempt to explain race differences are inadequate to inform health or social policy. CONCLUSIONS: Researchers should treat the race variable with the same degree of caution and skepticism with which it treats any other variable.

Bias↗
PubMed1993

The direction change concept for reticulospinal control of goldfish escape.

This is an analysis of whether biomechanical or kinematic variables are controlled by descending reticulospinal commands to the spinal cord during escape responses (C-starts) in the goldfish. We studied how the animal contracted its trunk musculature to orient an escape trajectory. We used trunk EMG recordings as a measure of the reticulospinal output to the musculature and we simultaneously gathered high-speed cinematic records of the resulting movements. We found that the escape trajectory is controlled by (1) the relative size of the agonist versus the antagonist muscle contractions on two sides of the body and (2) the timing between these contractions. We found no separate signal for forward propulsion (or force) apart from the initial stage 1 bending of the body. Rather, the neural specification of force is embedded in the commands to bend the body. Thus, our findings demonstrate the importance of the angular kinematic components, or direction changes, caused by the descending reticulospinal command. This new direction change concept is important for two reasons. First, it unifies the diversity of C-start movement patterns into a single and rather simple quantitative model. Second, the model is analogous to the systematic EMG and kinematic changes observed by others to underlie single joint movements of limbs in other vertebrates such as primates. As in these cases, the fish capitalizes on the mechanical properties of the muscle by setting the extent and timing of agonist and antagonist contractions. This, plus the fact that sensory feedback is likely to be minimal, may enable the animal to reduce the number of computational steps in its motor commands used to produce the escape response. Because horizontal body movements in fish are a fundamental vertebrate movement pattern produced by a highly conserved brainstem movement system, our findings may have general implications for understanding the neural basis of rapid movements of diverse body parts.

Animals↗