On the optimization of cholesterol screening.

Total serum cholesterol is a major risk factor for Coronary Heart Disease (CHD). Some guidelines have been published regarding treatment levels. However, before implementing cholesterol screening, the costs and benefits should be analyzed as a function of cholesterol level. Analysis is readily implemented on microcomputer spreadsheets using decision tree analysis. Because it is very difficult to establish some of the costs satisfactorily, the facility of spreadsheets in performing sensitivity analysis is crucial. Here, plausible numerical values are used as "default" conditions for estimating in a preliminary way the costs and benefits of a putative screening-intervention program. The cost-benefit condition remains very close to optimal over the range 200-240 mg/dl for cholesterol marker level. The optimal condition may shift considerably when the default parameter values are altered. With the default values, the maximal net benefit is around 5% of the estimated current costs of CHD deaths without screening.

Determining optimal screening policies using decision trees and spreadsheets.

The determination of the proportion of population to be screened, so that overall costs are minimized, is treated. A decision tree approach is used, based on knowing the probabilities and costs of all possible outcomes. This involves specifying models that estimate the prevalences in the screened and non-screened groups for various screening levels. The generalized implementation on a microcomputer spreadsheet that is presented permits sensitivity and optimality to be explored for different parameter conditions. A numerical example illustrates the results.

A model of the eustress system for health/illness.

The stress response system, as vital mediator of the individual's health/illness dynamics at physical, psychological, and social levels, is modeled through a systems approach. This extremely complex self-regulating system involves multiple causal factors, nonlinearities, and time delays. Key basic functions are surveillance, mobilization of resources, feedback, and purpose. The underlying physiological stress response comprises three main mechanisms: autonomic nervous system, hormonal system, and immune response system. Their afferent pathways are presented in a flow diagram, and integrated into the full system which includes the psycho-social dimensions. The main features of this overall system comprise: psycho-social dynamics, feedback and feedforward monitors, self-concept, evaluation and strategy-decision making, generalized coping resources, mobilization of response strategies, and behavioral control. Stressors, as potential producers of stress, are illustrated in the physical, psychological, and social domains. A U-shaped universal dose-response curve is helpful in understanding stressor-destressor actions. Destressors are similarly considered, with special relation to lifestyle. Finally, the concept of eustress is developed as the ideal condition toward which this complex homeostatic system works.

Biomedical engineering for "The Age of Health".

A systems approach to health care inevitably emphasizes shifting present emphasis from curative to preventive orientations. However, problems arise through the inertia and resistance of our politico-cultural system. The present highly-developed curative-oriented system depends heavily on technological and biomedial engineering expertise, as indeed will a preventive-oriented system. They must serve however within the priorities defined by the systems objectives in health care. This paper reviews, in terms of technological content and socio-political issues, some major developments including; multiphasic health testing and disease screening, health appraisals, clinical labs and other test procedures, protocols, computerized information systems, data bases and systems modelling.

A systems model of health behavior change.

The modeling in this paper is at the level of the individual, in relation to the subsystem of health behavior. It integrates social, environmental, psychological, and physiological factors to describe the health behavior change process. It is not intended to be quantitatively predictive of behavior change, since further development of this model is needed to determine the mathematical form of the relationships between variables. The model is innovative in several ways. First, it includes health-related variables and a rich feedback structure. In contrast, attitude behavior change models often cannot explain health behavior adequately, because they do not incorporate physiological variables. Second, the model can be easily used by educators to help identify important variables for developing health education curricula. Consequently, program developers are helped in determining program intents, teaching strategies, and learning activities, and evaluative strategies which are congruent with the attitude behavior change process.

Characteristics of neural transmission from the semicircular canal to the vestibular nuclei of cats.

1. The characteristics of the dynamic response of specifically canal-dependent neural units in cat vestibular nuclei have been examined during sinusoidal rotation of the head in decerebrate cats over the narrow frequency range 0.-1.7 Hz.2. Unit action potential frequencies were averaged on line from extracellular steel micro-electrodes stereotaxically located in the vestibular nuclei through the intact cerebellum.3. Action potential frequency was approximately in phase with stimulus angular velocity, the mean phase for forty-six units being + 11. degrees S.E. of the mean +/- 2.2 degrees ). Correction for a form of dynamic asymmetry reduced this value almost to zero.4. The mean gain of thirty-nine single unit responses was 0.76 S.E. +/- 0.08) AP/sec per degrees /sec. The gain varied as the (-0.28) power of stimulus angular velocity, for the five cells appropriately tested.5. A method was evolved for computing the spontaneous condition of cells, in terms of an equivalent spontaneous firing frequency, f(sp) irrespective of whether they were spontaneously active or silent. This f(sp) value was normally distributed about a mean value of 11.2 AP/sec (range + 70 to - 40 AP/sec).6. Directionality was examined in 116 units, of which 62% were ipsilateral (e.g. cells on left side excited by left-going rotational velocity) and 38% contralateral. Ipsilateral units proved easier to isolate and retain than contralateral ones.7. No significant differences in mean phase or gain were found in the sub-sets of spontaneously active/inactive cells and ipsilateral/contralateral cells.8. It is inferred that the cell population examined was a functionally homogeneous one in which the neural signal was closely tied to the angular velocity of canal rotation for the narrow band of sinusoidal rotational stimuli here employed. It is suggested that this signal is probably retained essentially intact in the ensemble neural message fed forwards from this region.

Frequency-response analysis of central vestibular unit activity resulting from rotational stimulation of the semicircular canals.

1. The neural response of semicircular canal-dependent units in the vestibular nuclei of cats has been examined over a frequency range of sinusoidal rotation extending from 0.004 to 0.9 Hz.2. Frequency-response analysis indicates that, over the range examined, the information contained in the neural signal received by the brain stem was similar to that expected from the mechanical end-organ.3. Over the experimental frequency range, the relation between neural response and mechanical stimulus was found to be dominated by a single time constant of about 4 sec, such that two response regions can be defined above and below a stimulus frequency of (1/4) rad/sec ( approximately approximately Hz).4. Above this frequency the information content of the neural signal tends towards that of angular velocity and below that frequency it tends towards that of angular acceleration.5. It is inferred (a) that the so-called ;long' time constant of the cat's horizontal canal is about 4 sec and (b) that during most normal head movements containing frequencies below about 1 Hz the informational mode of neural signals generated in the canal and received in the brain stem probably tends towards that of head angular velocity.6. This seems appropriate for the generation of vestibulo-ocular reflex compensation for head movement and for reflex damping (negative velocity feed-back) of unintended head and body movements.7. The average neural gain of central unit responses is estimated at 1264 action potentials/sec, per degree of cupular deflexion. This high value reflects the very small angles of cupular deflexion assessed on the basis of physical characteristics of the canal.8. The results permit a rough estimate of the elastic restoring coefficient of the cupula in the horizontal canal as 2.05 x 10(-3) dyne. cm.

A system model of the metabolic response to stress.

The dynamic interactions of the body's response to stress are extremely complex and can best be understood within the context of an information flow diagram. In this paper such a model is developed from the biochemical equations of glycolysis and from relevant hormonal and behavioral relations. In response to a situation perceived as stressful, the body prepares for physical action by the secretion of many hormones. These hormones mobilize fatty acids and initiate glucose sparing within the body. In modern living, little attitudinal or situational change is normally undertaken to reduce the perception of stress, and the hormones continue to be secreted. As a result, chronically high levels of fatty acids, ketones, cholesterol, and very low-density lipoproteins are maintained and contribute, in the long run, to an increased risk of cardiovascular disease. An examination of the flow diagram elucidates the possible pathways leading from the perception of stress to the pathological consequences of the body's response.