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PubMed2002

Computer simulation studies on the significance of lipid polar head charge.

Ripple phase modelling was achievable by taking into consideration the dipole structure of the polar heads of model membrane molecules. Computer simulations enabled the selective analysis of a model membrane. Considering only the hydrophobic part of the lipid membrane, the gel-fluid transition stage can be obtained in such a simulation. Assuming an additional degree of freedom, the entire molecule can move along the normal to the membrane surface projected from two C-C bonds. The amounts of shifted lipids were 17% and 33% at temperatures of 300 K (gel) and 330 K (fluid), respectively. Taking into account only polar head interactions in media of different ionic strength I, dielectric constant epsilon, and an effective charge and temperature, we could observe the same behaviour of the examined system independently of the values of I and ( when the charge was reduced to q/2. The amount of shifted heads at 300 K decreases sharply with the reduced charge value, with an accompanying increase in the number of "standing" polar heads. Summing up, it can be stated that hydrocarbon lipid chains exhibit a greater tendency to displacement in the fluid state than in the gel state. However, the polar heads behave in the opposite way: there are more displaced heads at 300 K than at 330 K. Thus, the overall analysis of the interactions between the molecules of the model membrane should enable us to find model parameters suitable for studying the lipid membrane at a wide range of temperatures. Finally, an electrostatic profile close to the membrane surface could be estimated in different membrane states. This should be useful in membrane-biologically active compound interaction analysis.

Computer Simulation↗
PubMed1975

Urea handling by the renal countercurrent system: insights from computer simulation.

The renal handling of urea has been investigated with the aid of a computer model of the countercurrent system in which active electrolyte reabsorption occurs along the entire ascending limb of Henle's loop. In this model, summarized in Fig.9, the buildup of a corticopapillary gradient for urea is optimized if there is net addition of urea to loops of Henle only in the outer medulla. This added urea remains within the tubular system until it is reabsorbed from collecting ducts in the inner medulla. Thus, a net transfer of urea from outer to inner medulla is accomplished (via distal tubule and cortical collecting duct). There is no net addition of urea to loops of Henle within the inner medulla; in this region, the loops act simply as countercurrent exchangers for urea. Computer simulation of systematic variation in the urea permeabilities of each nephron segment shows that interference with any element of the above schema results in impairment of the medullary accumulation of urea relative to plasma. Simulation of varying rates of urinary urea excretion demonstrates that this model can account for the ability of the kidney to excrete substantial amounts of urea without an accompanying osmotic loss of water. The major insight gained from this study is that net addition of urea to loops of Henle in the outer medulla greatly enhances the medullary accumulation of urea, whereas, net addition of urea to loops within the inner medulla tends to defeat such accumulation and hence the urinary concentrating process. This general principle applies also to an alternate model of the countercurrent system, in which electrolyte reabsorption from thin ascending limbs of Henle is passive.

Computers↗
PubMed1993

Computer simulations of the flexibility of a series of synthetic cyclic peptide analogues.

The flexibility of a series of cyclic peptides derived from the epitope of a snake toxin is investigated using computer simulation techniques. Molecular dynamics (MD) simulations and vibrational analyses are performed on chemically constrained peptides modeled on the parent protein loop. In the 50 ps MD simulations, large variations in the atomic fluctuations are seen between the peptides, and can be related to the nature of the chemical constraints present in the molecules. Normal mode analyses are performed on energy-minimized configurations derived from the dynamics trajectories. The atomic fluctuations calculated from the normal modes are about 30% of those of the molecular dynamics for the more flexible peptides and 70% for the more constrained molecules. The calculated differences in flexibility between the molecules are much less significant in the harmonic approximation.

Amino Acid Sequence↗
PubMed1992

The management of small abdominal aortic aneurysms: a computer simulation using Monte Carlo methods.

Many small abdominal aortic aneurysms can now be identified by ultrasound screening and it is necessary to decide whether the risks of enlargement and rupture justify elective surgery. A computer simulation of the behaviour of small aneurysms has been constructed using Monte Carlo methods to model patterns of enlargement and rupture. The effect of policy with regard to the observation and timing of intervention has been evaluated for different patient groups. The results demonstrate the value of early intervention in otherwise fit patients with expected operative mortality rates of 5% or below, whereas, for older patients (over 70 years old) 6-monthly screening and operation if the aneurysm exceeds 5 cm is suggested. Higher risk patients with expected operative mortality of over 10% may be better treated conservatively up to an aneurysm diameter of 7 or 8 cm. The method used for simulation is flexible, being easily adjusted to take account of new information, and may have applications in other areas of clinical decision making.

Aged↗
PubMed2006

Prediction of spinal canal expansion following cervical laminoplasty: a computer-simulated comparison between single and double-door techniques.

STUDY DESIGN: Laminoplasty was simulated using a computer-assisted technique to assess the amount of canal expansion. OBJECTIVES: This study was designed to clarify the relationship between laminoplasty opening size and increase in sagittal canal diameter, increase in canal area, and the angle of the opened lamina following laminoplasty, and to determine whether a spinous process-splitting laminoplasty achieves the similar canal expansion as a single open-door method. SUMMARY OF BACKGROUND DATA: Single and double-door cervical laminoplasty (SDCL and DDCL, respectively) have been widely used in the treatment of multilevel stenotic conditions. However, the relationship between laminoplasty opening size and spinal canal expansion following laminoplasty, and the comparison of postoperative spinal canal expansion between single and double-door techniques have not been well investigated. METHODS: SDCL and DDCL, based on preoperative computerized tomography scans of 34 patients who had undergone the laminoplasty surgery, were simulated using a computer-assisted technique. Laminoplasty with an opening size of 6, 8, 10, 12, 14, 16, and 18 mm were simulated to determine the amount of canal enlargement with the various opening size. RESULTS: Sagittal diameter, canal area, and lamina angle were increased steadily following either single or double-door laminoplasty with the door opened from 6 to 18 mm. Significant positive correlation was found between laminoplasty opening size and increase in sagittal diameter (R2 = 0.969 and P = 0.001 in SDCL; R2 = 0.926 and P < 0.001 in DDCL), increase in canal area (R2 = 0.961 and P < 0.001 in SDCL; R2 = 0.937 and P < 0.001 in DDCL), and lamina angle (R2 = 0.959 and P < 0.001 in SDCL; R2 = 0.943 and P < 0.001 in DDCL). No significant correlation was observed between preoperative sagittal diameter and increase in sagittal diameter of the spinal canal, whereas significant positive correlation was found between preoperative cross-section area and increase in cross-section area of the spinal canal. The differences between postoperative canal increase in sagittal diameter and canal area for the single versus double-door technique were statistically significant when the door was opened by more than 12 mm (P < 0.05). CONCLUSIONS: Our investigation provides insight into canal expansion after laminoplasty. The increased amount of canal following laminoplasty can be predicted by the regression equations. This may allow preoperative determination of the optimal size of the opening needed to establish adequate canal space for the spinal cord. Both single and double-door techniques of laminoplasty provide sufficient room for posterior migration of the spinal cord, although gaining different canal expansion.

Adult↗
PubMed2000

Optimum bitewing examination recall intervals assessed by computer simulation.

OBJECTIVE: To assess the effect of altering bitewing examination recall intervals on health gain from dental restorative treatment and to determine optimum recall intervals under varying clinical conditions. DESIGN: A computer simulation of the caries process in posterior approximal tooth surfaces. The effect of superimposing restorative treatment, based on diagnoses from bitewing radiological examinations carried out at differing time intervals, was incorporated. Input data included caries attack rates, median survival times of restorations, and sensitivity (Sn) and specificity (Sp) of treatment decision making by a high (A) and a low (B) performing dentist. PARTICIPANTS: A hypothetical population, initially 14-15 years old. INTERVENTIONS: Class II amalgam restorations. OUTCOME: Health gain in utility based units (UBUs) was assessed relative to interim end point UBUs pertaining under 'do nothing scenarios'. RESULTS: One thousand approximal surfaces, designated initially as 920 sound, 51 carious and 29 filled were followed in the model over 10 years. The greatest health gain (39.33 UBUs) was from dentist A (Sn = 0.23, Sp = 0.99, restoration median survival time = 20 years, caries rate = 4.4% per annum, optimal recall interval between bitewing radiological examinations = 7 months). The least was from dentist B (Sn = 0.52, Sp = 0.88, median survival time = 5 years. caries rate = 0.0% per annum, optimal recall interval between bitewing radiological examinations > 120 months) representing a loss of 16.79 UBUs compared with 'do nothing'. CONCLUSIONS: In the best interests of their patients, it would seem that dentists need to exercise considerable caution in making positive decisions to restore approximal tooth surfaces on the basis of bitewing radiographic evidence and that for some dentists current guidelines for bitewing examination intervals would appear to be too permissive.

Computer Simulation↗
PubMed1996

Does "Touching Four" on the Worth 4-dot test indicate fusion in young children? A computer simulation.

PURPOSE: "Touching four" dots on the Worth 4-dot test is used sometimes as an indication of fusion in young children. The authors examined the reliability of this test. METHODS: A computer simulation of the Worth 4-dot test generated images representing fusion, suppression, and alternate fixation. Sixteen children, ranging in age from 32 to 48 months, were examined using this test. RESULTS: None of the children could accurately describe the images verbally. Alternate fixation could not be distinguished from fusion by asking the subjects to touch the dots. Monocular suppression was identified accurately in all subjects. CONCLUSION: Touching four dots on the Worth 4-dot test does not distinguish fusion from alternate fixation in children with normal ocular alignment. This has important implications regarding the diagnosis of monofixation syndrome and assessment of the response to a prism adaptation trial in young children.

Adaptation, Ocular↗
PubMed2001

Mathematical modeling and computer simulation of erythrocytapheresis for SCD.

BACKGROUND: Erythrocytapheresis is used to prevent acute chest syndrome and stroke in patients with sickle cell disease (SCD). However, such regimens are associated with significant risks, such as iron overload and potential exposure to transfusion-transmitted infectious diseases. Computer modeling of erythrocytapheresis procedures may help optimize treatments and minimize risks. STUDY DESIGN AND METHODS: Mathematical models based upon material balance equations and patient-specific statistical analyses were developed to estimate HbS levels immediately after erythrocytapheresis and immediately before the next treatment. The equations were incorporated into a software application that was used to model the effects of various treatment values on four patients treated with 90 erythrocytapheresis procedures. RESULTS: Immediate postprocedure HbS values were accurately estimated with correlations between measured and calculated values ranging from R(2) = 0.83 to 0.96. Estimates of HbS just before the next treatment correlated well in three patients (R(2) = 0.71 to 0.83) but poorly in one (R(2) = 0.28 to 0.46). Varying the treatment values by computer simulation led to a wide variation in the number of RBC units and the net RBC volume transfused. CONCLUSION: Computer modeling of erythrocytapheresis can be used to optimize chronic treatment regimens for SCD patients and potentially to minimize the risks of overtransfusion.

Anemia, Sickle Cell↗
PubMed1993

Counterflow in isotachophoresis: computer simulation and experimental studies.

A computer model has been developed to predict the effects of co- and counter-current flows on electrophoretic transport. Model predictions are compared with experimental data obtained with the large-scale recycling isotachophoresis apparatus, recently developed in our laboratory. There were no significant changes in the steady state properties or the transient development of the Kohlrausch-adjusted profiles with and without flow. The application of counterflow in free flow isotachophoresis in early stages, before a steady state is achieved, can result in selective wash-out of slower sample components. Thus, the magnitude of counterflow can be used as a variable in optimizing separations. The characteristic features of the model render it also suitable for the simulation of electroosmotic flow in capillary electrophoresis in open tubes, where plug-type flow prevails.

Anions↗
PubMed1988

Gap junction uncoupling and discontinuous propagation in the heart. A comparison of experimental data with computer simulations.

The effects of octanol on longitudinal propagation in guinea pig papillary muscles were measured by intracellular microelectrodes. These data were compared with alterations in conduction induced by stepwise removal of gap junction channels in computer simulations of propagation based on a discontinuous cable model. Octanol reduced the velocity (theta) of propagating action potentials (APs) from 53.2 +/- 3.5 to less than 6.6 +/- 2.1 cm/s before block occurred. The maximal rate of rise (Vmax) changed in a biphasic manner, increasing from 133.1 +/- 5.4 in controls to 201.7 +/- 11.0 V/s when theta was 20.5 +/- 2.8 cm/s, and then declining to less than 58.6 +/- 15.2 V/s just before block. The input resistance and time constant of the AP foot increased, and the ascending limb of phase-plane loops became increasingly nonlinear and notched during octanol treatment. All effects of octanol reversed upon washout. A strand of cardiac tissue was modeled as a discontinuous cable composed of 40 cells, each with 10 isopotential membrane segments described by Beeler-Reuter kinetics, and coupled by a variable number of gap junction channels (156 pS). Decreasing the number of channels from 40,000 to 400 to 60 slowed conduction from 62.6 to 16.4 to 3.1 cm/s. As noted in the experimental data, Vmax increased from 103 to 130 and then fell to less than 96 V/s. The AP foot increased and became nonexponential. Distinct notches developed during phase 1 of the APs at slower propagation velocities in the experiments and simulations. The close similarities between the experimental and theoretical data obtained in this study supports the applicability of a discontinuous cable model for describing longitudinal propagation in the heart.

1-Octanol↗
PubMed1992

[A computer simulated test for the long-time change of heterozygote. Analysis of possibility on preserving the heterozygote for long-time in population].

Under the conditions of random mating and selecting. The research by computer simulation analysed the possibility of long-time conserving heterozygote in colong. An important conclusion was obtained. It was impossible to conserve heterozygote for a long time in colong. Therefore it is not necessary to control inbreeding for conserving all genes of colong by reducing gene purity in the work of conserving breeds for farm animal and poultry.

Animals↗
PubMed1993

Computer simulations of the effects of different synaptic input systems on motor unit recruitment.

1. The effects of four different synaptic input systems on the recruitment order within a mammalian motoneuron pool were investigated using computer simulations. The synaptic inputs and motor unit properties in the model were based as closely as possible on the available experimental data for the cat medial gastrocnemius pool and muscle. Monte Carlo techniques were employed to add random variance to the motor unit thresholds and forces and to sample the resulting recruitment orders. 2. The effects of the synaptic inputs on recruitment order depended on how they modified the range of recruitment thresholds established by differences in the intrinsic current thresholds of the motoneurons. Application of a uniform synaptic input to the pool (i.e., distributed equally to all motoneurons) resulted in a recruitment sequence that was quite stable even with the addition of large amounts of random variance. With 50% added random variance, the recruitment reversals did not exceed 8%. 3. The simulated monosynaptic input from homonymous Ia afferent fibers generated a twofold expansion of the range of recruitment thresholds beyond that attributed to the differences in the intrinsic current thresholds. The Ia input generated a small reduction in the number of recruitment reversals due to random variance (6% reversals at 50% random variance). The simulated monosynaptic vestibulospinal input generated a twofold compression of the range of recruitment thresholds that exerted a modest increase in the number of recruitment reversals (12% reversals at 50% random variance). 4. In comparison with the modest effects of the two monosynaptic inputs, the simulated oligosynpatic rubrospinal excitatory input exerted a nine-fold compression in the recruitment threshold range that resulted in a recruitment sequence that was highly sensitive to random variance. With 50% added random variance, the sequence became nearly random (40% reversals). 5. Reciprocal Ia inhibition was simulated by a uniform distribution within the pool, but its effects on recruitment order were highly dependent on the distribution of the excitatory input. Reciprocal inhibition exerted only minor effects on recruitment order when combined with the Ia or vestibulospinal inputs. However, when the excitatory drive was supplied by the rubrospinal input, even small amounts of reciprocal inhibition were sufficient to completely reverse the normal recruitment sequence. 6. The simulated monosynaptic Ia input was highly effective in compensating for the disruptive effects of rubrospinal excitation on recruitment order. Even a small Ia bias combined with the rubrospinal excitation was sufficient to halve the effects of random variance and to restore the normal recruitment sequence in the presence of rather large amounts of reciprocal inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2002

The catalytic power of ketosteroid isomerase investigated by computer simulation.

Ketosteroid isomerase (KSI) catalyzes the isomerization of Delta(5)-3-ketosteroids and Delta(4)-3-ketosteroids at very high rates. Here we examine the principles underlying the catalytic efficiency of KSI by computer simulations using the empirical valence bond method in combination with molecular dynamics free energy perturbation simulations. The simulations reproduce available kinetic and structural data very well and allow us to examine several features of the catalytic mechanism in detail. It is found that about 60% of the rate enhancement is due to stabilization of the negatively charged dienolate intermediate by hydrogen bonding. The critical H-bond between Tyr16 and the intermediate is found to be a normal ionic H-bond with the preferred proton location on the tyrosine residue. The remaining 40% of the catalytic effect originates from a reduction of the reorganization energy of the reaction. The possibility of an active site water molecule occupying the empty cavity adjacent to the catalytic base (Asp40) is also addressed. The existence of such a water molecule could explain how the enzyme manages to maintain a low pK(a) for the general base residue.

Binding Sites↗
PubMed1989

An evaluation of the effectiveness of a computer simulation of anaesthetic uptake and distribution as a teaching tool.

Gas Man is an interactive, microcomputer-based simulation and tutorial designed to teach the principles of anaesthetic uptake and distribution. Using two resident groups, one at a primary university-teaching hospital and the other at a medical school affiliated community hospital, the authors compared residents' knowledge of the subject prior to exposure to the tutorial and the average time spent using the program during a self-paced instruction period. Both groups not only significantly improved their knowledge of uptake and distribution 8 weeks after using this program, but wished to spend additional time with it, implying that it was a pleasant and satisfying way to learn. Computer simulation has the potential to be an important teaching tool in an anaesthesia residency training programme.

Anesthesiology↗
PubMed1997

Acute coronary artery deficiency treatment process. Managing scarce resources and maintaining a level of service with the help of computer simulation.

Surgical treatment can be planned well in advance or arrive in a near emergency. If careful control is not exercised there is always the possibility that patients may suffer as a result. Discrete event simulation is an effective tool which can be used to find the most efficient ways of managing such a service's timetable. Examines the application of a desktop computer simulation package to model the work of a cardiac diagnosis and treatment system. The simulation package suggests how efficiency might be improved by moderating times taken to complete activities and staff and other resources required to perform the activities. Suggests the principles outlined can be readily expanded into a more complex model.

Acute Disease↗
PubMed1976

Computer simulation of the precordial QRS complex: effects of simulated changes in ventricular wall thickness and volume.

The cardiac electric field generated by depolarization of the human ventricle is simulated with a computer model which utilizes 1,500 dipoles. The configuration of the ventricles utilized in the model assumed that the cross-sectional shape of the left ventricle was circular and the right ventricular free wall was a portion of an ellipse. The torso was assumed to be homogeneous and infinite. The activation sequence was based on the measurements of Durrer. The depolarizational wave was simulated by dipole layers. The output of the model is presented as a standard multilead precordial ECG. The ECG complexes generated by the model closely resemble the precordial QRS complexes of normal man. Simulated increases in wall thickness (1 to 2.2 X control) were associated with changes in the calculated precordial QRS complexes which were characteristic of left ventricular hypertrophy. Voltage (R in V5 or V6 and S in V1) and QRS duration increased linearly as a function of calculated left ventricular mass. Increases in ventricular activation time were related nonlinearly to changes in left ventricular mass and did not occur in the absence of a simulated increase in wall thickness. The effects of simulated changes in left ventricular volume (0.6 to 3.0 X control) on the QRS complex were mainly dependent on the resultant increase in left ventricular mass. This model may be useful in simulating the precordial QRS complexes that result from isolated or combined changes in ventricular volume or wall thickness or other disorders of the heart. Furthermore, it may be useful whenever a simulation of a QRS generator is needed.

Cardiac Volume↗
PubMed1991

Assessment of split-sample proficiency testing for cholesterol by use of a computer simulation model.

We developed a computer model to study the use of patients' specimens to assess compliance of cholesterol measurement performance with the 1992 goals of the Laboratory Standardization Panel of the National Cholesterol Education Program. The model uses Monte Carlo techniques to simulate cholesterol measurements that are subject to both systematic and random error. Split-sample measurements by a clinical laboratory and by a reference laboratory are compared by using linear regression to estimate clinical laboratory bias and imprecision; subsequently, according to specified decision limits, the performance of the clinical laboratory is classified as acceptable or deficient. We have quantified the influence of the bias and imprecision of the clinical laboratory, the imprecision of the reference laboratory, the number of split samples compared, and the decision limits on the accuracy of the classification of clinical laboratory performance. Unless the decision limits are carefully selected and a sufficient number of split samples are used, clinical laboratory performance will be frequently misclassified.

Cholesterol↗
PubMed2003

[The computer simulating prediction method of noise of underground garage in urban residential region].

The model of random point sound source was applied to predict the noise of underground garage in urban residential region with the method of computer simulating. Comparing the predict data and the data of measurement, the precision of this model was good. The model can be applied to predict the influence of the noise of new built underground garage noise, it can offer the reference for the planning department.

Computer Simulation↗