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PubMed1986

Computer simulation of bend propagation by axoplasmic microtubules.

The generation of bending waves by microtubules in squid nerve axoplasm has been modelled using appropriately modified versions of computer programs developed previously for simulation of flagellar bending waves. The results confirm that a constant longitudinal force directed along the axis of the microtubule is sufficient to cause the generation of regular oscillations and propagated bending waves when the forward gliding movement of the microtubule is obstructed. No control mechanism is required to modulate the active force-generating system. In order to obtain bending waves similar to those observed experimentally, it was necessary to use a model for the force-generating system in which the active force decreases with increasing sliding velocity. If the elastic bending resistance of axoplasmic microtubules is similar to that of microtubules in sperm terminal filaments, the longitudinal force per unit length generated by the axoplasmic microtubules must be of the same order of magnitude as the force generated by dynein arms along the doublet microtubules of eukaryotic flagella.

Animals↗

PubMedDate not supplied

Computer simulation of geometry and hemodynamics of canine pulmonary arteries.

Assuming that along the pulmonary arteries, mathematical expectations of branching are equal to matrix (Ei,j; i: parent branch class, j: daughter branch class number), we made computer drafts of patterns of pulmonary arterial branching trees from the published data of canine pulmonary arterial casts with the "Monte Carlo methods" by FORTRAN, calculating from these data, the numbers of branches, size and resistance of the trees. We also analyzed blood flow distribution in a pulmonary branch according to the pathlength from the entrance of the tree. The graphics of the trees were similar to the original arterial casts, and numbers of the branches were nearly the same as the previous reported values. Calculated resistance was reasonable. The rate of blood flow per unit vessel in the short pathlength group was calculated as 1.5 times that of the long pathlength group of the same diameter. We believe that our method of describing the branching pattern matrix (Ei,j) provides a reasonable simulation of complex branching patterns such as pulmonary arteries and a useful means to analyze local hemodynamics.

Animals↗

PubMed2003

The effect of the interval between blood pressure determinations on the delay in the detection of changes: a computer simulation.

UNLABELLED: The frequency of automated noninvasive blood pressure (NIBP) measurements during routine anesthesia is a balance between potentially deleterious effects of frequent cycling and a delay in detecting changes caused by a long cycle time. A computer model generated systolic blood pressures that changed to a new, random value after a period of stability. We sampled these data at intervals between 1 and 10 min to simulate NIBP measurements. A separate algorithm, based on Trigg's Tracking Variable, indicated when a change had been detected. For each set of variables, the simulation was repeated 1000 times, and the average time to detect a change was recorded. The mean time to detect a change was 8.0 min with a 1-min cycle, 8.9 min with a 2-min cycle, 10.8 min with a 5-min cycle, and 13.0 min with a 10-min cycle. As the cycle time increased, the delay in detecting changes increased but only by approximately half the increase in the cycle time. The optimum variables for the trend detection algorithm also changed as the NIBP interval increased. Provided that abrupt changes in blood pressure are not anticipated, a 1- or 2-min cycle time for NIBP offers little advantage over a longer period. IMPLICATIONS: We used a computer model to study the effect of increasing noninvasive blood pressure (NIBP) sampling interval on the detection of blood pressure changes. The detection time increased only 50% of the increase in the sampling interval. This information may help optimize NIBP intervals in different circumstances.

Algorithms↗

PubMed1997

Computer simulation of circulation in patient with total cavo-pulmonary connection: inter-relationship of cardiac and vascular pressure, flow, resistance and capacitance.

The aim is to develop a computer model representative of the circulation in a patient with a uni-ventricular heart surgically palliated by a total cavo-pulmonary connection (TCPC). The effects of known hazardous exposures on this type of circulation are investigated. A model of the cardiovascular system is built using standard components such as transmission lines, restrictors and capacitances. The chamber of the heart consists of a volume connected to checkvalves, and an oscillating source flow connected to the volume represents the pumping of the heart. The following are simulated: exposure to cold, heat, high altitude, accelerating forces, blood loss, reduction in ventricular function, atrioventricular-valve regurgitation and treatment with afterload-reducing agents. During simulations, all the parameters can be changed, independently of each other, and the resulting changes in flow, resistance and pressure are recorded. Exposure to cold, reduced ventricular function and atriventricular-valve regurgitation result in a decrease in cardiac output (14, 58 and 45%, respectively). At high altitude, an increase of 18% is noted in the central venous pressure. Afterload-reducing agents increase the cardiac output by 8% and reduce central aortic pressure by 23%. Blood loss results in a marked reduction in perfusion pressure. It is concluded that the computer model is a useful instrument for simulation of a TCPC or Fontan circulation. The original criteria for this surgical procedure are those showing the most marked haemodynamic responses to different stimulus.

Computer Simulation↗

PubMed1974