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Results for “Models, Cardiovascular”

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At least 19 recordsLinked to original sources
PubMed1990

[A realistic cardiovascular model for evaluating clinical applicability of duplex and color-Doppler equipment].

To evaluate the accuracy and reliability of colour-coded Doppler devices (CCDD) for practical use, a circulatory phantom with in vivo characteristics was developed. The experimental design consists of a piston-diaphragm metering pump with an adjustable piston volume and frequency of stroke as well as silicone tubings with different elasticity and diameters comparable with cadaver arteries. Depending on physiological conditions, blood as a circulating fluid and the surrounding soft tissues of the artery near the Doppler probe should be employed. The transducer should be manually guided. Thus, comparable to physiological frequency spectral displays, different types of wave forms (e.g. monophasic, triphasic) were initiated to analyze the reliability of CCDDs for practical use.

Blood Flow Velocity↗
PubMed1991

[CO2 angiography: studies of gas filling of vessels and assessing the factors of influence on the injection process with a cardiovascular model].

Following the advent of digital subtraction angiography (DSA), carbon dioxide gas has become a useful contrast agent for arterial angiography. Former manual injection methods had precluded accurate dosing and reproducibility. An original gas injector was therefore developed and tested in a circulatory system model. This permitted an accurate evaluation of vascular gas-filling. it also proved possible to measure the injection parameters taking different influencing factors into account. It was shown that vessels up to 10 mm in diameter are virtually completely filled with gas. In vessels larger than 10 mm in diameter, a residual fluid level remains, which in turn reduces the possibility for complete vessel imaging. The injection flow is dependent primarily on the vascular circulation rate, vessel diameter and the inclination of the vessel. With respect to other factors examined, neither catheter size, number of holes nor the direction of the injection have any relevant influence.

Angiography, Digital Subtraction↗
PubMed1995

[A nomogram of duplex ultrasound quantification of peripheral arterial stenoses. Studies of the cardiovascular model and in angiography patients].

BACKGROUND AND METHODS: Blood flow velocity measurements were performed with duplex ultrasound in vitro (flow phantom) and in 62 patients who underwent angiography due to peripheral vascular disease. RESULTS: Intrastenotic peak systolic velocity (PSV) divided by proximally recorded PSV (peak velocity ratio, PVR) exhibited a strong correlation with percent diameter reduction: r2 = 0.86; N = 106 stenoses. A PVR value > or = 2.4 indicated a more than 50% stenosis with a sensitivity of 87% and a specificity of 94%. Calculation of PVR may normalize for patient variation and allow noninvasive quantification of lumen narrowing with high sensitivity and specificity. The intraobserver variability (95% CI) of stenosis quantification using PVR values was 10%. A nomogram simplifies estimation of lumen narrowing after measurement of intrastenotic and proximal PSV values. CONCLUSION: Quantification of peripheral artery stenoses can be performed easily and noninvasively with duplex ultrasound using the peak velocity ratio (PVR).

Aged↗
PubMed1989

[A stress-dependent pulsatile cardiovascular model as the basis for regulating artificial hearts].

The development and simulation of closed-loop control of blood pumps requires a pulsatile model of the cardiovascular system that takes into account the natural mechanisms of adaptation during exercise. In this article, a model is described which takes account of the baroreceptor reflex, the change in heart rate, contractility of the heart, and the peripheral resistance during exercise, as well as venous tone, and the nonlinearity of vessel compliance. In addition, a model of the artificial heart is presented, in which the nonlinear limitation of the stroke volume is taken into account, and the concept of a pulse frequency modulated (PFM) control system for the circulation with an artificial heart is described.

Heart Rate↗
PubMed1996

A novel video technique for visualizing flow structures in cardiovascular models.

We describe a video system that produces good quality images of particle trajectories in seeded fluid flows. The operation of a liquid crystal optical shutter and a modified charge-coupled device (CCD) camera were synchronized to generate images of particle trajectories which were stored in a framegrabber before being transferred to S-VHS tape. The camera system is particularly appropriate for visualizing transient or unsteady flows in models of the cardiovascular system as the integration time may be varied to produce particle trajectories of variable length.

Cardiac Output↗
PubMed1984

A cardiovascular model for studying impairment of cerebral function during +Gz stress.

A digital computer model of the human cardiovascular system has been developed which can be used for studying impairment of cerebral function during +Gz stress. The model includes simulation of the arterial and venous systems, the heart, baroreceptor control of heart rate, control of venous tone, and the effect of gravity. Model predictions suggest that, for unprotected subjects, carotid pressure at eye level decreases to 50 mm Hg (beginning of peripheral light loss) at approximately 2.7 Gz. The pressure decreases to 20 mm Hg (beginning of central light loss) at approximately 3.6 Gz. An anti-G suit provides an extra 1.1 to 1.5 Gz protection. Even though blood pressure supplying retinal vessels drops significantly at the above G levels, cerebral blood flow is maintained due to protective and compensatory mechanisms. These observations compare favorably with results reported in the literature. The results suggest that this model can be used to improve our understanding of the cardiovascular system's response to +Gz stress.

Aerospace Medicine↗
PubMed1989

Data for cardiovascular modeling.

Data are required for a meaningful approach to quality and cost-conscious cardiovascular care. How to identify the types of data available and their sources, advantages and limitations to their use, issues involved in combining data from different sources for decision modeling and some possible solutions are discussed in this summary of the Working Group on Data for Cardiovascular Modeling.

Cardiovascular Diseases↗
PubMed1989

Projects and priorities in cardiovascular modeling.

Studies that either 1) model the likelihood of clinical outcomes as a function of patient characteristics, or 2) examine the factors underlying a specific medical decision are discussed. Although the currently available models represent important contributions, the working group that met during the 1987 Regenstrief Conference identified several important areas for further attention. Described are discussions on ways to improve standardization, accessibility, validation and dissemination of decision models.

Aged↗
PubMed2004

A method for matching the refractive index and kinematic viscosity of a blood analog for flow visualization in hydraulic cardiovascular models.

In this work, we propose a simple method to simultaneously match the refractive index and kinematic viscosity of a circulating blood analog in hydraulic models for optical flow measurement techniques (PIV, PMFV, LDA, and LIF). The method is based on the determination of the volumetric proportions and temperature at which two transparent miscible liquids should be mixed to reproduce the targeted fluid characteristics. The temperature dependence models are a linear relation for the refractive index and an Arrhenius relation for the dynamic viscosity of each liquid. Then the dynamic viscosity of the mixture is represented with a Grunberg-Nissan model of type 1. Experimental tests for acrylic and blood viscosity were found to be in very good agreement with the targeted values (measured refractive index of 1.486 and kinematic viscosity of 3.454 milli-m2/s with targeted values of 1.47 and 3.300 milli-m2/s).

Biomechanical Phenomena↗