Biomedical subjects

C P Valcke

Publications and source records attributed to C P Valcke.

6 recordsLinked to original sources

PubMed1999

Automated heparin-delivery system to control activated partial thromboplastin time: evaluation in normal volunteers.

BACKGROUND: Unfractionated heparin is used widely; however, control of the level of anticoagulation remains its greatest problem, with fewer than 35% of patients having activated partial thromboplastin times (aPTTs) within a range of 55 to 85 seconds in recent trials. METHODS AND RESULTS: We developed and tested a prototype of an automated heparin control system (AutoHep) in which a computer-based titration algorithm adjusted the heparin infusion to reach a target aPTT. In 1 study, 12 healthy male subjects received an intravenous infusion of heparin with the rate determined by AutoHep and were randomized to receive an initial bolus or no bolus of heparin preceding the infusion. A second study evaluated the automated blood sampling system in 12 subjects. Of the 344 end-point aPTT measurements, 78% were within +/-10 seconds of the target (prespecified primary end point), and 89% were within a +/-15-second range. The time to achieve a target aPTT was 93 minutes without and 150 minutes with an initial heparin bolus. The total percentage of time within the target range +/-15 seconds was 46 of 48 hours (96%). The automatic blood sampling system successfully obtained 96% of all scheduled samples. CONCLUSIONS: These results suggest that the AutoHep system has the potential to significantly improve aPTT control of intravenous heparin compared with current clinical practice.

Adult↗

PubMed1997

Closed-loop drug infusion for control of heart-rate trajectory in pharmacological stress tests.

The diagnosis of coronary artery disease (CAD) is an important task in the management of cardiology patients. Recently, the use of pharmacological stress testing has become available as an alternative to exercise stress testing (ETT). A new system (device-drug combination) was developed specifically for the diagnosis of coronary artery disease. The system uses a novel catecholamine, arbutamine, which is infused intravenously to increase heart rate (HR) and cardiac contractility in order to evoke signs of ischemia. The development of a closed-loop control algorithm for the delivery of this drug and a pharmacodynamic (PD) model representing the HR response to arbutamine infusions are presented. Model parameters are estimated from clinical data on normal volunteers and patients. Based on this mathematical model, a rule-based control algorithm is designed. The structure of the control algorithm is discussed and testing of the algorithm based on simulations and animal and human trials are summarized. Results from clinical trials shows that the algorithm controls the HR increase according to a selected trajectory. The automated delivery of the drug can provide the cardiologist with an efficient, effective, and safe method for administering a pharmacological stress test.

Algorithms↗

PubMed1989

A programmable system for acquisition and reduction of respiratory physiological data.

A portable software package (TIDAL--Tools for Intelligent Data Acquisition in the Laboratory) for acquiring and analyzing respiratory physiological data is described. TIDAL supports flow-, volume-, and concentration-measuring devices, and any other instruments that produce linear analog outputs. The system allows users to specify the names and types of channels to be sampled, and the calculations involved in reducing samples to breath-to-breath values. The specification of channels and calculations is given in EDL, an Experiment Description Language designed for respiratory physiology. EDL comprises a set of internal functions (primitives) which can be combined into arbitrarily complex expressions. To simplify EDL programming, TIDAL includes a macro processor and a standard macro library; the library contains definitions for a wide variety of respiratory variables. Examples are inspiratory and expiratory times and total volumes, mean inspired and expired gas volumes and concentrations, and end-tidal concentrations. Variables that are derived from these primary data, such as respiratory quotient, are also easily specified. TIDAL is written entirely in the C programming language, with special attention to portable coding practices. The code is organized in a modular structure that eases porting to multiple hardware/compiler/operating system environments.

Expert Systems↗

PubMed1989

Recursive identification of lung parameters.

Determination of lung capacity (FRC) using insoluble gas washout or equilibrium methods is a common procedure in respiratory tests. The lung model can be extended to include multiple compartments with differing volumes and ventilation fractions. A discrete-time mathematical model of a multi-compartment lung was developed based on mass conservation laws of the gas exchange. To estimate the unknown parameters in the model from experimental data, a recursive prediction error algorithm was implemented. The design of the algorithm provides the capability to track time-varying parameters, such that the system can be monitored on-line. Determination of the model order may be as important as estimation of the parameters, especially in biological systems where little may be known about the structure. Two new criteria to distinguish between models of varying complexity, the 'minimum description length principle' and the 'accumulated prediction error', are illustrated. Theoretical studies show that these criteria yield consistent order estimates of the process. Simulations and experimental data confirm the feasibility of this approach for the estimation of lung parameters.

Algorithms↗

PubMed1989

An extended soluble gas exchange model for estimating pulmonary perfusion--I: Derivation and implementation.

A dynamic model for respiratory exchange of blood soluble gas is described. This model includes a general treatment of tidal breathing, an inhomogeneous lung comprising multiple distensible compartments, and nonlinearities due to multiple-gas effects. The motivation for this new model is the continuing interest in estimating pulmonary perfusion from measurements of respiratory soluble gas exchange. Numerical simulation can be employed to investigate the errors that result from simplifications made in the derivations of simpler models used for this purpose. Examples of such simplifications are the assumptions that ventilation is constant and unidirectional, and that multiple soluble gases can be independently modeled. These results can delimit the boundaries within which perfusion estimates can be considered reliable. An example demonstrating the model and its numerical solution is presented.

Models, Biological↗

PubMed1989

An extended soluble gas exchange model for estimating pulmonary perfusion--II: Simulation results.

The assumptions made in deriving models of soluble gas exchange used for continuous estimation of pulmonary perfusion are critically examined. Comparisons are made between estimation algorithms based on simple and more complex models. The more complex model includes a general treatment of tidal breathing, an inhomogeneous lung comprising multiple distensible compartments, and nonlinearities due to multiple-gas effects. The results show that sensitivity of perfusion estimates to errors inherent in simple linear models. These errors can invalidate the estimates under realistic physiological conditions. Concentration and multiple-gas effects, for example, can cause substantial estimation errors. Large ventilations relative to lung volume can also lead to errors. These simulations can be used to delimit the conditions under which the estimates can be considered reliable. A further set of simulations is used to assess the sensitivity of perfusion estimates to errors in the assumed values of unknown or approximately known model parameters. Inadequate specification of the compartmental structure of the lung (distributions of ventilation/perfusion and ventilation/volume) can cause large estimate errors. Precise estimates of lung tissue volume do not appear to be necessary. These results are important for the practical application of soluble gas methods for pulmonary perfusion determination. In both sets of simulations, it is shown that parameter estimate accuracy must be confirmed independently of goodness-of-fit criteria. Close agreement between predicted and observed end-tidal concentrations does not ensure accurate perfusion estimates.

Computer Simulation↗