Virtual and Artificial Cardiorespiratory Patients in Medicine and Biomedical Engineering

Abstract

Recently, 'medicine in silico' has been strongly encouraged due to ethical and legal limitations related to animal experiments and investigations conducted on patients. Computer models, particularly the very complex ones (virtual patients-VP), can be used in medical education and biomedical research as well as in clinical applications. Simpler patient-specific models may aid medical procedures. However, computer models are unfit for medical devices testing. Hybrid (i.e., numerical-physical) models do not have this disadvantage. In this review, the chosen approach to the cardiovascular system and/or respiratory system modeling was discussed with particular emphasis given to the hybrid cardiopulmonary simulator (the artificial patient), that was elaborated by the authors. The VP is useful in the education of forced spirometry, investigations of cardiopulmonary interactions (including gas exchange) and its influence on pulmonary resistance during artificial ventilation, and explanation of phenomena observed during thoracentesis. The artificial patient is useful, inter alia, in staff training and education, investigations of cardiorespiratory support and the testing of several medical devices, such as ventricular assist devices and a membrane-based artificial heart.

Keywords: artificial patient; cardiopulmonary interaction; extracorporeal membrane oxygenation; gas exchange; hybrid model; membrane-based cardiovascular support systems; modeling and simulation; virtual patient.

Figure A1

A part of the computer screen during the work of the Tgol.e-spirometry system for e-learning of spirometry. An example that may explain to students the h-shaped flow–volume loop that is observed in severe obstructive lung diseases. The thin line is the loop observed by physicians, and the bold line is the loop that would be if only airflow from lungs could be observed (the difference between both loops is caused by air exhaled from collapsing bronchi at the beginning of the forced expiration).

Figure A2

Spirometry measurements of the artificial patient (the hybrid respiratory simulator). (a) ‘healthy’ patient; (b–e)—mild, moderate, severe and very severe COPD caused by narrowing of bronchi; (f) COPD of mild severity caused by a decrease of lung tissue elasticity.

Figure A3

Examples of forced spirometry—scans of spirometer reports. The flow–volume curves registered during three spirometric measurements of real (a) and artificial (b) patients suffering from severe obstructive lung disease. Spirometry was performed three times in each of these cases. Note the high repeatability in the case of the artificial patient.

Figure 1

The idea of the cardiopulmonary hybrid platform developed by the authors. As oxygen delivery and carbon dioxide removal are the fundamental goals of the cardiorespiratory system, the model of gas transfer and exchange is the central point (it consists of modules of AGT—airways gas transfer, GE—gas exchange, BGT—blood gas transport). Respiratory system mechanics influences AGT, GE, and circulation. Cardiovascular system mechanics influences BGT and GE. Respiration and circulation support as well as oxygenation/decarbonation can be simulated or realized with physical devices by means of impedance converters playing the role of numerical–physical interfaces. V, Q, P and F denote volumes, airflows and pressures in the respiratory system, and blood flows, respectively.

Figure 2

An example of the physical–numerical interface: A real ventilator ventilates the tube that simulates the trachea. Without respect to the type of a respirator and the support mode, the respirator work changes the pressure in the tube. That pressure is measured and converted to voltage ([p/U]), which after digitization ([A/D]) is the input (P) of a computer model. The model calculates the air flow (F) that would be for the measured pressure course in a real patient. This calculated value (converted to voltage Fu) controls the air flow source; in consequence, a quantity of the real air flows through the tube. Such flow causes a pressure change in the tube as though the air has gone to/from the real lungs. Thus, from the respirator point of view, it ventilates a real patient.