Pediatric bed fall computer simulation model: Parametric sensitivity analysis

Falls from beds and other household furniture are common scenarios that may result in injury and may also be stated to conceal child abuse. Knowledge of the biomechanics associated with short-distance falls may aid clinicians in distinguishing between abusive and accidental injuries. In this study, a validated bed fall computer simulation model of an anthropomorphic test device representing a 12-month-old child was used to investigate the effect of altering fall environment parameters (fall height, impact surface stiffness, initial force used to initiate the fall) and child surrogate parameters (overall mass, head stiffness, neck stiffness, stiffness for other body segments) on fall dynamics and outcomes related to injury potential. The sensitivity of head and neck injury outcome measures to model parameters was determined. Parameters associated with the greatest sensitivity values (fall height, initiating force, and surrogate mass) altered fall dynamics and impact orientation. This suggests that fall dynamics and impact orientation play a key role in head and neck injury potential. With the exception of surrogate mass, injury outcome measures tended to be more sensitive to changes in environmental parameters (bed height, impact surface stiffness, initiating force) than surrogate parameters (head stiffness, neck stiffness, body segment stiffness).     

A computer simulation model of a rubella epidemic

This paper presents a deterministic computer simulation model of the rubella epidemic process. The model consists of four difference equations which relate the number of infectant individuals in a closed population to the number of susceptible individuals, the number of immune individuals, the contact rate, the birth and death rates, and the proportion of vaccinated susceptibles. After computer simulation, the model is validated using data from the East North Central section of the United States. Satisfactory agreement between predicted and reported cases is obtained. It is demonstrated that under reporting of actual cases is a significant factor in modeling the epidemic process. The efficiency of various vaccination programs in eradicating rubella is investigated.     

Dynamic control of hepatic glucose metabolism: Studies by experiment and computer simulation

The rates of storage and release of carbohydrate by the liver are deterined by the plasma concentrations of several bloodborne signals; most important are the concentrations of glucose, and the hormones insulin and glucagon. To understand the complex control relationships of these three signals as they affect the liver, their individual dynamic influences have been determined experimentally, and they have been integrated by means of a computer simulation of the pathways of hepatic glycogen metabolism. The simulation studies have led to specific hypotheses about the biochemical effects of glucose and insulin on the liver. The simulation studies have also led to the conclusion that glucose exerts a rapid moment-to-moment influence on the rate of uptake of glucose by the liver. Insulin, however, by exerting a slower influence on the sensitivity of the liver to glucose, is very effective in “optimizing” the amount of glucogen with the liver stores during food intake. Thus, integrated experimental and simulation studies can lead to a view of a physiological regulating system which does not emerge from either approach used alone.     

Validation of a head-neck computer model for whiplash simulation

A head-neck computer model was comprehensively validated over a range of rear-impact velocities using experiments conducted by the same group of authors in the same laboratory. Validations were based on mean ±1 standard deviation response curves, i.e. corridors. Global head-neck angle, segmental angle and local facet joint regional kinematic responses from the model fell within experimental corridors. This was true for all impact velocities (1.3, 1.8 and 2.6 ms⁻¹). The non-physiological S-curvature lasted approximately 100 ms. The present, comprehensively validated model can be used to conduct parametric studies and investigate the effects of factors such as active sequential and parallel muscle contractions, thoracic ramping and local tissue strain responses, as a function of cervical level, joint region and impact velocity in whiplash injury assessment.     

Analogue computer model of the human cardiovascular control system

A simplified analogue computer model of the human cardiovascular control system is developed in this paper. This model can be adjusted to reproduce the response of a subject to a submaximal work-load. The validity of the model is evaluated and suggestions for its further development are included.     

Chinese hamster cells with a minichromosome containing the centromere region of human chromosome 1

We describe a series of primary and secondary hamster-human hybrids which have selectively retained a small amount of human DNA. The hybrid XJM12.1.3 contains an estimated 4000–8000 kb of human DNA, and for a secondary hybrid derived from it, XEW8.2.3, our estimate is 1000–2000 kb. The hybridization of Southern blots of DNA from these hybrids with a variety of human satellite DNA probes reveals that these lines include centromere sequences of human chromosome 1. The identifiable human DNA is in the form of a minichromosome, as detected by in situ hybridization in the light microscope and in the electron microscope. At mitosis, the minichromosome can be observed to have kinetochores and to be associated with microtubules. Therefore, it can segregate in a stable fashion. It may be significant that in the selection of the hybrids we had selected for a human gene which has been mapped on human chromosome 1.     

Renal corpuscular hydrodynamics: Digital computer simulation

Summary A mathematical model of the renal corpuscle is presented and used to quantify the effect on filtration rate, nephron blood flow and hydrostatic pressure in the glomerular capillaries of variations in: 1. the hydrostatic pressure in Bowman's space; 2. the hydrodynamic resistances of the afferent and efferent arterioles; 3. the ultrafiltration coefficient of the glomerular membrane; 4. the hydrostatic pressure in the peritubular capillaries; 5. the arterial haematocrit and plasma protein concentration. The model is derived from the principle of conservation of mass and volume. Hydrostatic pressure gradients along the glomerular capillaries are neglectec. The hydrodynamic resistances of the afferent and efferent arterioles are assumed to be determined by two independent factors, one being determined by the vascular dimensions, the other by the haematocrit. Blood flow is considered to be related in a linear manner to the hydrostatic pressure decreases along these vessels. The effect of changing the hydrostatic pressure in Bowman's space on nephronGFR was calculated and found to agree with experimental measurements. When corpuscular hydrodynamics are related to variations in the hydrodynamic resistance of the afferent or efferent arteriole it is seen that the change in efferent arteriolar plasma flow accompanying altered nephronGFR is very sensitive to the way in which the change is produced. In contrast changes in glomerular capillary pressure and filtration fraction are insensitive. The calculations indicate that differences measured in nephronGFR between superficial and juxtamedullary nephrons can be explained by assuming that the diameters of the afferent and efferent arterioles of the juxtamedullary nephrons increase in direct proportion to the diameter of the renal corpuscle.     

Evaluation in health informatics: computer simulation

The evaluation of complex medical informatics applications involves not only the information system, but also its impact on the organizational environment in which it is implemented. In instances where these applications cannot be evaluated with traditional experimental methods, computer simulation provides a flexible approach to evaluation. The construction of a computer simulation model involves the development of a model that represents important aspects of the system under evaluation. Once validated, the model can be used to study the effects of variation in system inputs, differences in initial conditions and changes in the structure of the system. Three examples are discussed, namely, a wide-area health care network, physician order entry into a hospital information system, and the use of an information system designed to prevent medical errors that lead to adverse drug events in hospitals.     

Parvalbumins and muscle relaxation: a computer simulation study

Summary The distribution of Ca²⁺ and Mg²⁺ among the regulatory cation binding sites of troponin (T-sites) and the strong, Ca²⁺-Mg²⁺ binding sites of troponin and parvalbumins (P-sites) in the sarcoplasm of a muscle was calculated. At rest, 60% of the T-sites were metal free, while 92% of the P-sites were loaded with Mg²⁺.In response to a Ca²⁺ pulse, troponin-calcium (T-Ca) complexes were rapidly formed, while the binding of Ca²⁺ to P-sites was limited by the slow rate of dissociation of the parvalbumin-magnesium (P-Mg) complexes. Muscle activation was not prevented by a high content of parvalbumins.Parvalbumin and the sarcoplasmic reticulum (SR) pump were complementary relaxing factors that removed Ca²⁺ from the cytosol and from the T-sites. Parvalbumins dominated the first part of relaxation, while the action of the SR was essential to ensure the return to a very low level of free Ca²⁺ ion and of T-Ca. After relaxation, a large fraction of the Ca²⁺ pulse was still bound to parvalbumins and returned slowly to the SR during the recovery.When the SR activity was reduced, the presence of parvalbumins preserved a fast rate of relaxation, at least for a few contractions. This may have a high adaptive value in cold-blooded animals. Ed. notation: Free calcium ion (free Ca²⁺); bound calcium ion (bound Ca²⁺).     

On the peripheral bladder control system of the dog and urodynamics:In vivo characterisation and hybrid computer simulation

A quantitative model of the peripheral bladder control system of the dog is developed. This model is based on the experimental characterisation of the detrusor muscle and the urethra in 25 female dogs. Intravesical pressure, urinary flow and bladder volume were simultaneously recorded during electrical bladder stimulation, and, from these data, a dynamic model of the bladder control system has been deduced. A general equation for predicting urinary flow patterns is developed, and the hybrid computer EAI-690 is used to simulate the evacuation of the bladder. The effect of different parameters of the system on the micturition pattern is investigated in detail. This work may have interesting clinical applications: for example, in the development of adequate techniques for the evacuation of the paraplegic bladder. Also, the experimental procedures elaborated in this study could be applied in the diagnosis of bladder function and urethral obstruction. Indeed, we have been able to characterise the detrusor muscle and the urethra independently using clinically accessible variables.     

Social mechanisms in the population genetics of Tay-Sachs and other lethal autosomal recessive diseases: a computer simulation model

A computer simulation model was developed to study the effects of various feudal social customs on the incidence of lethal autosomal recessive genes. Populations of 500 individuals were created in which each person was characterized by sibship, genotype, and sex. The numbered sibships were sorted into numerical order. Each individual then sought a mate from 6 or 12 sibships on either side of his or her own sibship. The resulting couples were sorted in order of the husband's sibship number, after which the couples produced children in accordance with the prevailing birth rate. This ordering of sibships made the probability of a gene remaining in one locality higher than the probability of it drifting to distant localities. A lethal autosomal recessive gene was introduced into populations at a starting carrier rate of 10%. This fell after 20 generations to 2.54 +/- 0.17% (SEM) which was significantly less than the 5.00% carrier rate predicted by a deterministic model in which random mating occurred in an infinite population. The excessive loss of the lethal gene was caused by the high incidence of consanguineous marriages and by the occurrence of random inequalities in the distribution of the gene. The avoidance of sib marriages raised the final carrier frequency (3.28 +/- 0.19%) as did reproductive compensation (4.33 +/- 0.26%). The combination of the incest taboo and reproductive compensation raised the final carrier rate to 5.05 +/- 0.28%. It is concluded that the social factors which may have operated over a period of many centuries in the past have had a significant effect on the population genetics of lethal autosomal recessive genes.     

A computer program for analysis of chromosome abnormalities

A computer program was made for the statistical analysis of a large number of abnormal karyotypes and for studies on the relationship between chromosomal abnormalities and clinical features of diseases. The program is based on the disintegration of abnormal karyotypes and the identification of types of abnormalities, chromosome numbers, and breakpoints on chromosomes. The frequencies of abnormalities could be tabulated in a given population according to type, chromosome number, and breakpoints.