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PubMed1981

Cortical anatomy, size invariance, and spatial frequency analysis.

In a recent application of an algorithm developed in computer and optical pattern recognition, Cavanagh has suggested that a composite of spatial frequency mapping and complex logarithmic mapping would provide translationally, rotationally, and size-invariant mechanism for human vision. In this work, Cavanagh has not made explicit the fact that this transformation is composite, that is, that the first step (global Fourier analysis) perceptually, anatomically, and physiologically inconsistent with primate vision, but that the second step (complex logarithmic mapping) is actually embodied in the anatomy of the primate retinostriate projection. Moreover, it is the complex logarithmic remapping step which is entirely responsible for the computational simplification of the symmetries of size and rotation invariance. These facts, which have been extensively discussed in a recent series of papers, are briefly reviewed and illustrated. Furthermore, it is shown that the architecture of the retinostriate map may provide an example of computational anatomy in vision, such that the spatial representation of a stimulus in the brain may be of direct functional significance to perception, and to the nature of certain visual illusions.

Afterimage↗

PubMed1976

Computer-aided investigations of respiratory data.

In the first part of this paper a computerised evaluation of plethysmographic signals is presented. The off-line processing described eliminates some erroneous simplifications that routine plethysmography is bound to involve. (1) A subtraction of the box pressure baseline permits measurements with perfectly sealed constant volume plethysmographs even in the case of thermal disequilibrium. (2) Alveolar pressure is computed from the box pressure signal, using instantaneous values of the intrathoracic gas volume. (3) This technique enables one to utilise all the measured data for determinations of airway resistance and viscous work, thus yielding more exact values as compared to the graphic evaluations. In Part 2 a three-parameter model of transpulmonary mechanics, applied to fit data of cat experiments, is described. The aim of this study is to demonstrate how transpulmonary parameters (static pleural pressure, compliance and resistance) are modified by the actual state of the pulmonary vascular bed.

Airway Resistance↗

PubMed1989

Ergonomic aspects of cold stress and cold adaptation.

In contrast to the simplified, unvarying, and rigidly controlled conditions that characterize laboratory studies of human responses to cold, normal work in cold regions is characterized by a complex and unstable thermal environment, intermittent cold exposure and exercise, and the freedom to adjust clothing and activity for comfort. These "ergonomic" aspects profoundly modify the impact of a cold environment on people's health, comfort, and performance. A review of recent field studies in the Antarctic shows that the supposed "tropical microclimate" of clothed people in the cold is an over-simplification. People tend to be alternately chilled and overheated, and the accompanying exercise of the vascular responses provides a potential stimulus for vasomotor adaptation. Significant and substantial changes in men's responses to standardized whole-body cold exposures, observed on eight Antarctic expeditions, show that general acclimatization to cold develops as an increase in tissue insulation, which is mediated by an enhanced vascular response to cold.

Acclimatization↗

PubMed1986

Quantitative affinity chromatography: increased versatility of the technique for studies of ligand binding.

The potential of affinity chromatography for the characterization of strong solute-ligand interactions is explored by studying the NADH-dependent elution of rabbit muscle lactate dehydrogenase from a column of trinitrophenyl-Sepharose in 0.067 M phosphate, pH 7.2. An interesting development is the simplification of the general affinity chromatography theory that emanates from the use of affinity matrices with a high concentration of immobilized reactant groups. The resultant expression allows evaluation of the intrinsic association constant for solute-ligand interactions from a single series of either zonal or frontal affinity chromatographic experiments conducted in the presence of a range of free ligand concentrations. Thus, contrary to previous belief, an affinity matrix designed for solute purification work should prove to be an asset for, rather than an impediment to, the study of solute-ligand interactions by quantitative affinity chromatography.

Adsorption↗

PubMed1994

Automated method for characterization of diastolic transmitral Doppler velocity contours: late atrial filling.

We develop an automated method of characterizing the late atrial filling phase of diastole by fitting a kinematic model for diastolic filling to the clinical Doppler A-wave contour. The result is a set of model parameters which completely characterizes the contour. We have previously derived a parameterized diastolic filling (PDF) model, which predicts the time-dependent transmitral blood flow velocity obtained by Doppler echocardiography. An automated method to determine the PDF model parameters for early rapid filling from the clinical Doppler E-wave has also been developed and validated. The method consists of digitizing the acoustic Doppler waveform, recreating the Doppler velocity profile, extracting the maximum velocity envelope, and fitting the PDF model for early filling to the envelope. In the current work, we apply the same general approach for PDF parameter determination for the late atrial filling phase of diastole. To assess the presence and significance of near-degeneracies in the model parameter set, numerical experiments (consisting of fitting the model to a model-generated contour to which Gaussian noise was added) were performed. These revealed a two-dimensional degeneracy in four-dimensional parameter space which could be removed by using two kinematic simplifications: critical damping and resonant forcing. We show that these degeneracy-eliminating approximations do not limit the ability of the model to predict clinical A-wave contours.

Atrial Function↗

PubMed1988

Radionuclide ventriculography (equilibrium gated blood pool scanning)--its present clinical position and recent developments.

Myocardial scanning (MS) and radionuclide ventriculography (RNV) are the foundation of nuclear cardiology. These procedures aim in two completely different directions: RNV tries to image heart motion, that is, mechanical (pump) function, and therefore belongs to the group of first-order functional imaging (FI, imaging mechanical function), whereas MS is based on myocardial metabolism, and therefore can be attributed to third-order functional imaging (metabolism). This statement is relevant for the assessment of the clinical position of RNV: Third-order (metabolism) functional imaging is the domain of nuclear medicine (NM), whereas first-order FI has to face the competition of alternative noninvasive procedures such as ultrasound (US), digital subtraction angiography (DSA), computer tomography (CT), and nuclear magnetic resonance (NMR). The domain of RNV includes stages two (acute infarction) and three (postinfarction period) of coronary arterial disease (CAD). The advantageous combination of quantitative data on global, left ventricular (LV) function and imaging of regional motion ensures the superiority of RNV over US. However, RNV is inferior to MS in physical examinations in the preinfarction stage of CAD, whereas US is clearly inferior to both NM procedures. Recent progress could be attained by gated SPECT (GASPECT). A proposal is presented for simplification of this time-consuming procedure. Technetium-labeled isonitriles offer the chance for the combination of "perfusion-motion" imaging of the myocardium. However, even standard RNV offers new possibilities. The multitude of parameters produced by quantitation has not yet been exploited completely. This can be done by discriminant analysis. The computer finds out an optimal subset from the whole set of parameters for the solution of a significant clinical problem. The software "learns" to find the "label" of a special pathognomonic entity. This computer work is supported by a relational data bank (Oracle) and an optical disk. Two examples for the effectiveness of the computer in problem solving are presented. It is concluded that RNV, even in the very competitive class of first-order functional imaging, enjoys a preferred position. The future indeed seems brighter because labeled isonitriles offer the chance for the combination of perfusion-motion imaging of the myocardium.

Coronary Disease↗

PubMed1994

Arm position constraints when throwing in three dimensions.

1. Overarm throwing is a skilled multijoint movement with potentially many degrees of freedom. Considering only the arm > or = 7 degrees of freedom are involved (shoulder 3, elbow 2, wrist 2). For each arm segment 3 degrees of freedom are potentially required to specify its angular position (orientation) at any moment during a throw. Simplification of the control problem for the CNS would occur if there were constraints on these degrees of freedom. The objective was to determine whether such constraints exist at ball release when throwing at targets in different directions using only the arm. 2. The angular positions in three dimensions of the distal phalanx of the middle finger, the hand, the forearm, and the upper arm were simultaneously recorded with search coils as subjects sat with a fixed trunk and threw balls at nine targets in an approximate +/- 40 degree work space. Ball release was signaled by microswitches on the proximal and distal phalanges of the middle finger (proximal and distal triggers). 3. On throwing at any one target the hand at ball release adopted a similar orientation for each throw, i.e., for a particular vertical and horizontal angular position the hand adopted a similar torsional position. On throwing at targets throughout the work space, angular position (rotation) vectors describing hand positions in space at ball release were confined to a two-dimensional surface rather than a three-dimensional volume. This constraint in hand torsion occurred near and at ball release but not throughout the entire throw. It was not due to mechanical factors because such a surface was not obtained when subjects deliberately twisted their arms when throwing. Thus at ball release during a "natural" throw the hand was constrained to 2 of its possible 3 angular degrees of freedom. 4. The same constraint was also found for finger, forearm, and upper arm angular positions in space at ball release as determined at both the proximal and distal triggers. A consequence is that at ball release the entire arm was constrained to 2 of its possible 7 degrees of freedom. 5. The two-dimensional position vector surface for each arm segment was similar to that obtained when pointing with a straight arm at the same targets. In both cases they showed torsion and were twisted like the surface obtained by rotations around the horizontal and vertical axes of a Fick gimbal. However, in some subjects the throwing surfaces were tilted from the vertical.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1991

[Search for emboligenic heart disease in case of ischemic cerebral accidents].

The demonstration of a cardiac source of systemic embolism in patients who have suffered a cerebral ischemic event may have important therapeutic implications. This explains the large demand for echocardiography and Holter monitoring in these patients. The frequency of cerebral embolism of cardiac origin, the simplification of the diagnostic approach by non-invasive investigations and the precision of ultrasound techniques explains the tendency towards the indiscriminate generalisation of this attitude. However, the large number of potential patients for investigation, the limited facilities of investigation and the incertitude over the responsibility of certain cardiac abnormalities with respect to the context and age, are arguments in favour of a more selective investigative approach. The keystone of diagnosis is careful history taking and clinical examination with interpretation of the ECG and chest X-ray. Three clinical situations may then be identified: 1) A cardiac abnormality known to be highly embolic is diagnosed from the outset (e.g. mitral stenosis, valve prosthesis, endocarditis, myocardial infarction). The diagnostic work-up is no longer etiological: echocardiography may show intracardiac thrombi or a valvular vegetation, reinforcing the causal relationship, but the complementary investigations are mainly useful for evaluation the cardiac disease and for deciding on curative or preventive therapy. 2) A cardiac abnormality is diagnosed but its responsibility is doubtful due to its high prevalence and low embolic potential. This is the case of patients with mitral valve prolapse, mitral annular calcification, calcific aortic stenosis and VVI pacing. Complementary investigations are not discriminative for the etiological diagnosis of the cerebral embolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗

PubMed1991

[Private accident insurance in Switzerland with reference to liability insurance as a part of social security].

On the Swiss market there exist various different accident insurance schemes and systems. Private accident insurance which is offered by the private insurers, date back to the middle of the 19th century. Since 1912 accident insurance is compulsory for all employees working in particularly dangerous industries, since 1984 it covers all employees in the country. In Switzerland there exists no general compulsory accident insurance. To perform as insurance carriers are qualified: private insurance companies, the Swiss Accident Insurance Company, and a number of the social health (sickness) insurers. Depending on the insurance system there are different approaches to renumerate the health costs. In the various social insurance systems the patient is rather free to chose his doctor and hospital (among those who have a contract with the insurer); in private insurance he is completely free. Yet the billing systems and the applicable rates and tarifs differ considerably. There are trends to simplify these systems and bring them more into mutual accordance. Due to the important rise of the health costs in Switzerland, there exists the danger that possible simplifications will bring about more public influence yet less private initiative and less incentives to really control costs without lessening the patients' possibilities.

Humans↗

PubMed1995

A continuum theory for the prediction of lateral and rotational positioning of alpha-helices in membrane proteins: bacteriorhodopsin.

We have developed a new method for the prediction of the lateral and the rotational positioning of transmembrane helices, based upon the present status of knowledge about the dominant interaction of the tertiary structure formation. The basic assumption about the interaction is that the interhelix binding is due to the polar interactions and that very short extramembrane loop segments restrict the relative position of the helices. Another assumption is made for the simplification of the prediction that a helix may be regarded as a continuum rod having polar interaction fields around it. The polar interaction field is calculated by a probe helix method, using a copolymer of serine and alanine as probe helices. The lateral position of helices is determined by the strength of the interhelix binding estimated from the polar interaction field together with the length of linking loop segments. The rotational positioning is determined by the polar interaction field, assuming the optimum lateral configuration. The structural change due to the binding of a prosthetic group is calculated, fixing the rotational freedom of a helix that is connected to the prosthetic group. Applying this method to bacteriorhodopsin, the optimum lateral and rotational positioning of transmembrane helices that are very similar to the experimental configuration was obtained. This method was implemented by a software system, which was developed for this work, and automatic calculation became possible for membrane proteins comprised of several transmembrane helices.

Amino Acid Sequence↗

PubMed1985

[Procedures of therapeutic action in geriatric psychiatry (apropos of dementia states)].

In order to exist, geriatric psychiatry must have its roots in action to help the patients, the family and the caring staff. This approach to psychiatry must be directed both at the present situation of the patient and at the future of the disease. However, in order to act, one must introduce a meaning and a direction which become determined through action. In this context, the symptomatological approach is often hindered by a tendency to over-simplification and reductionism due to terminological flaws and to the inadequacy of its underlying rigid concepts. Such an approach is hindered also by the very nature of a type of medical practice, which establishes the observation of behaviours before making a therapeutic decision and starting treatment. Thus we can contrast two therapeutic procedures in relation to the dementias. On the one hand, a classical view which procedes from diagnosis to treatment. Its aim is to develop precise etiological and physiopathogenic references. Its objective is to eradicate disease and obtain a cure. On the other hand, another--contemporary and complementary--approach begins at the point of the patient's difficulties. These difficulties define the therapeutic aims, and from these, the appropriate symptomatology can be selected. This approach puts an emphasis on care and rehabilitation. It constantly throws back upon us the need to think about the quality of our work and allows us to avoid a clumsy use of the available resources. It provides the basis for the development of new alternative knowledge and introduces a new spirit into medicine from which demented patients will surely benefit.

Aged↗

PubMed1982

Low spatial-frequency channels in human vision: adaptation and masking.

Previous work showed that adapting to low spatial frequency gratings (below 1.5 cycles/degree) may cause maximal spatial adaptation at a significantly higher spatial frequency. It has been suggested that there are no adaptable spatial-frequency channels tuned to below 1.5 c/deg. Contrary to this view, we found that adaptation and masking with low spatial frequencies (0.12-1.0 c/deg) produced maximal threshold elevations when the test patterns were the same spatial frequency as the adapting or masking pattern. These results were obtained using test patterns that turned on and off gradually or sharply. The results suggest that there are form mechanisms optimally sensitive to very low spatial frequencies. Adaptation was selective to position (phase) and orientation at low spatial frequencies; masking was observed to be selective to orientation at a spatial frequency as low as 0.2 c/deg. A clear dichotomy between transient, motion channels and sustained, form channels at low spatial and temporal frequencies may represent an unrealistic simplification. There may exist directionally-selective motion mechanisms sensitive to very slow motion, and these may play a role in the discrimination of form. The discussion considers the bandwidths of the low spatial frequency mechanisms.

Adaptation, Ocular↗

PubMed1989

Evaluation and simplification of the World Health Organization clinical case definition for paediatric AIDS.

The World Health Organization (WHO) clinical case definition for paediatric AIDS was tested during a 1-month period on 221 consecutive hospitalized children in Kigali, Rwanda. Relevant clinical features not included in the WHO case definition were also evaluated. Thirty-four out of the 221 children (15.4%) were HIV seropositive. Although the specificity of the WHO case definition was high (92%), the sensitivity and the positive predictive value (PPV) were low (41 and 48%, respectively). The following individual signs had a PPV at least equal to the complete WHO case definition: chronic diarrhoea (47%), respiratory distress secondary to lower respiratory tract infection (50%), oral candidiasis (53%), parotitis (67%), generalized lymphadenopathy (88%), and herpes zoster infection (100%). When logistic regression analysis was done on the nine variables included in the WHO case definition, confirmed maternal infection was the best predictive variable for HIV seropositivity in children (P less than 10(-5). We further excluded the serological status of the mother from the analysis and performed a stepwise logistic regression analysis on the 18 clinical signs and symptoms for which information had been collected. Those signs and symptoms contributing the most to the regression were: respiratory distress, chronic diarrhoea and generalized lymphadenopathy. Based on these findings, we propose a simplified clinical case definition for paediatric AIDS in Africa with better sensitivity, specificity and PPV than the WHO case definition. Further work is needed using this approach to develop case definitions useful for epidemiological surveillance and for case management.

Acquired Immunodeficiency Syndrome↗

PubMed1985

Animal models of self-destructive behavior and suicide.

In this article we have addressed selected aspects of animal models that may have ramifications in our understanding of suicide and human self-destructive behavior. It should be kept in mind that these human behaviors have many determinants. In considering animal models, we do not propose that similar behaviors necessarily have the same causation nor that a particular experimental manipulation that produces a behavioral syndrome in one species will produce that response in another species. Even if environmental conditions or the resulting behaviors vary for different species, the biochemical intermediaries may be similar. The simplification inherent in the laboratory modeling of an aspect of human behavior should not mean that the complexity of the human syndrome be forgotten. However, if a simple explanation can account for the production of a particular behavioral syndrome in animals, it can help to structure our thoughts regarding the etiology of the behavior in humans. The ethologic observations discussed in this article may help to place human self-destructive behavior in a continuum with that of animals in the wild. Although care should be given to drawing direct parallels, the clear conclusion is that humans are not alone in exhibiting self-initiated behaviors that ultimately produce self-harm or death. Whereas laboratory models have been extensively used for modeling psychiatric illnesses or for producing specific pharmacologic manipulations of the CNS, surprisingly little attention has been given to the modeling of self-destructive behaviors themselves. Emphasis on self-destructive behaviors, as well as on their biologic and genetic underpinnings, represent an important future direction for work on animal models in psychiatry.

Altruism↗

PubMed1991

Protein folding and association: insights from the interfacial and thermodynamic properties of hydrocarbons.

We demonstrate in this work that the surface tension, water-organic solvent, transfer-free energies and the thermodynamics of melting of linear alkanes provide fundamental insights into the nonpolar driving forces for protein folding and protein binding reactions. We first develop a model for the curvature dependence of the hydrophobic effect and find that the macroscopic concept of interfacial free energy is applicable at the molecular level. Application of a well-known relationship involving surface tension and adhesion energies reveals that dispersion forces play little or no net role in hydrophobic interactions; rather, the standard model of disruption of water structure (entropically driven at 25 degrees C) is correct. The hydrophobic interaction is found, in agreement with the classical picture, to provide a major driving force for protein folding. Analysis of the melting behavior of hydrocarbons reveals that close packing of the protein interior makes only a small free energy contribution to folding because the enthalpic gain resulting from increased dispersion interactions (relative to the liquid) is countered by the freezing of side chain motion. The identical effect should occur in association reactions, which may provide an enormous simplification in the evaluation of binding energies. Protein binding reactions, even between nearly planar or concave/convex interfaces, are found to have effective hydrophobicities considerably smaller than the prediction based on macroscopic surface tension. This is due to the formation of a concave collar region that usually accompanies complex formation. This effect may preclude the formation of complexes between convex surfaces.

Algorithms↗

PubMed1991

The volume conductor effects of anisotropic muscle on body surface potentials using an eccentric spheres model.

The purpose of this paper is to determine the volume conductor effects of muscle anisotropy on body surface potentials using an eccentric spheres model with a uniform double layer source configuration. Previous eccentric spheres work assumed that cardiac muscle anisotropy was small and that skeletal muscle effects could be accounted for by boundary extension, i.e., by scaling the conductivities and dimensions. However, in this paper, anisotropy for both the myocardium and the skeletal muscle is explicitly incorporated into the eccentric spheres volume conductor model. The anisotropy is treated as having uniform orthogonal components in the radial and tangential directions for both the skeletal muscle and myocardium. The solution for Laplace's equation is written in a series expansion of appropriate basis functions for each region. In the isotropic regions spherical harmonics with integer radial dependence and Legendre polynomial azimuthal dependence are utilized. For the anisotropic regions, Legendre polynomials are still appropriate for the azimuthal dependence, but noninteger powers of radial dependence are required. The approximate representation for anisotropy, i.e., the boundary extension method for the skeletal muscle and a scaled homogeneous conductivity without boundary extension for the myocardium are compared with explicit representations for the two regions. Two basic conclusions are drawn from the results. First, the treatment of skeletal muscle anisotropy by the boundary extension method is a valid and useful simplification which yields errors of 2% for the peak body surface potential. The second conclusion drawn from this study is that myocardial anisotropy has a significant effect on the magnitude of body surface potentials.(ABSTRACT TRUNCATED AT 250 WORDS)

Electric Conductivity↗

PubMed1980

The gestalt of occlusion--A clinical appraisal.

1. Occlusion, with its many ramifications, cannot be over simplified. It should not be considered so varied that a sequential and subtle analysis of its ramifications defies simplification. 2. The same mechanisms produce the correct or incorrect physiologic position of the dental units. A faulty mechanism must be recognized and all efforts made to return it to efficiency as soon as possible for the benefit of the entire system. 3. The correct physiologic terminal position of the mandibular condyles is the ideal relationship in the TMJ and activates the posterior component forces of the neurologic system. This forms the dentition into its most harmonious relationship. 4. Any teminal position of the condyle in the mandibular fossa, other than the physiologic terminal position, compromises the potential of a harmonious interdental forming process. The results range from simple deflective occlusal contacts to severe malocclusions. 5. The constancy of the occlusal plane relationship, easily determined from a cephalometric tracing offers a clinical guide as to its best functioning position. 6. A TMJ radiographic technique that ensures repeatable, reproducible, and traceable radiograms is an essential diagnostic aid. It is necessary to know the position of the condyle in the fossa before, during, and after procedures that alter the interocclusal relationship. 7. Not all TMJ problems are necessarily symptomatic. Occlusal adjustment procedures should be utilized to ensure a harmonious interocclusal relationship manifest by the muscles of mastication functioning in a nonsymptomatic, optimal, and physiologic manner, in all working jaw relations. The ideal physiologic terminal position must be established as closely as possible during saliva swallowing. 8. Only occlusal adjustment techniques utilizing the natural forces of the neuromuscular system to reestablish the ideal physiologic terminal position within the TMJ should be used. A technique such as that developed by Long satisfies this requirement. 9. Although there are many imperfections in knowledge, there are no imperfections in truth.

Cephalometry↗