PubMed Health⌕ Search

Biomedical subjects

M Guarini

Publications and source records attributed to M Guarini.

6 recordsLinked to original sources
PubMed1999

Flow properties of fast three-dimensional sequences for MR angiography.

To reduce the scan time of time of flight or phase contrast angiography sequences, fast three-dimensional k-space trajectories can be employed. The best 3D trajectory depends on tolerable scan time, readout time, geometric flexibility, flow/motion properties and others. A formalism for flow/motion sensitivity comparison based on the velocity k-space behavior is presented. It consists in finding the velocity k-space position as a function of the spatial k-space position. The trajectories are compared graphically by their velocity k-space maps, with simulations and with an objective computed index. The flow/motion properties of various 3D trajectories (cones, spiral-pr hybrid, spherical stack of spirals, 3DFT, 3D echo-planar, and shells) were determined. In terms of flow/motion sensitivity the cones trajectory is the best, however, it is difficult to use it for anisotropic resolutions or fields of view. Tolerating more flow sensitivity, the stack of spirals trajectory offers more geometric flexibility.

Blood Flow Velocity↗
PubMed1999

An expert system for monitor alarm integration.

OBJECTIVE: Intensive care and operating room monitors generate data that are not fully utilized. False alarms are so frequent that attending personnel tends to disconnect them. We developed an expert system that could select and validate alarms by integration of seven vital signs monitored on-line from cardiac surgical patients. METHODS: The system uses fuzzy logic and is able to work under incomplete or noisy information conditions. Patient status is inferred every 2 seconds from the analysis and integration of the variables and a unified alarm message is displayed on the screen. The proposed structure was implemented on a personal computer for simultaneous automatic surveillance of up to 9 patients. The system was compared with standard monitors (SpaceLabs PC2), using their default alarm settings. Twenty patients undergoing cardiac surgery were studied, while we ran our system and the standard monitor simultaneously. The number of alarms triggered by each system and their accuracy and relevance were compared. Two expert observers (one physician, one engineer) ascertained each alarm reported by each system as true or false. RESULTS: Seventy-five percent of the alarms reported by the standard monitors were false, while less than 1% of those reported by the expert system were false. Sensitivity of the standard monitors was 79% and sensitivity of the expert system was 92%. Positive predictive value was 31% for the standard monitors and 97% for the expert system. CONCLUSIONS: Integration of information from several sources improved the reliability of alarms and markedly decreased the frequency of false alarms. Fuzzy logic may become a powerful tool for integration of physiological data.

Blood Gas Analysis↗
PubMed1999

A model of internal control may improve the response time of an automatic arterial pressure controller.

A simplified model for the arterial pressure control system was implemented on a personal computer using Matlab Simulink. Model responses to variations of systemic vascular resistance were comparable to those predicted by physiology. Computer simulation suggested that including this model of the internal pressure control system within the design of an external controller would achieve better arterial pressure control and faster response than previous systems.

Blood Pressure↗
PubMed1998

Estimation of ventricular volume and elastance from the arterial pressure waveform.

We propose that it is possible to estimate cardiovascular parameters from the arterial pressure waveform, including ventricular maximal elastance and end-diastolic volume, if cardiac output is also known. We tested this hypothesis by means of a parameter estimation algorithm applied to simulated arterial pressure signals. The program first estimated three coefficients representing products of passive parameters from the diastolic part of the simulated arterial pressure waveform. Second, it estimated three parameter products pertaining to the ventricular function from the systolic part of the waveform. Third, mean blood flow was entered, enabling the program to compute individual parameters. This program was tested on 200 computer-generated arterial pressure signals, obtained by simulating the model with random but bounded parameters. Correlation between estimated parameters with those actually used in the simulations was excellent. Even though the value of this computer simulation is limited to the simplified model used and requires experimental validation, it demonstrates that the technique is theoretically feasible.

Blood Flow Velocity↗
PubMed1998

Estimation of cardiac function from computer analysis of the arterial pressure waveform.

This paper presents a method for estimating parameters of a cardiovascular model, including the left-ventricular function, using the sequential quadratic programming (SQP) and the least minimum square (LMS) algorithms. In a first stage, a radial arterial-pressure waveform with corresponding cardiac output are used to automatically seek the set of parameters of the diastolic model. Computer simulation of the model using these parameters generate a pressure waveform and a cardiac output very close to those used for the estimation. In a second stage, the estimated arterial load parameters are used to select the best left-ventricular model function, from four different possibilities, and to estimate its optimum parameter values. The method has been tested numerically and applied to real cases, using data obtained from cardiovascular patients. It has also been subjected to preliminary validation using data obtained from laboratory dogs, in which cardiovascular function was artificially altered.

Algorithms↗