Virtual respiratory system for education and research: simulation of expiratory flow limitation for spirometry

Due to economic and ethical problems, virtual organs may appear more convenient than experiments on animals or limited investigations on patients. In particular, a virtual respiratory system (VRS) may be useful for tasks such as respirators and support methods testing, education, staff (medical and technical) training, (initial) testing of scientific hypotheses.

A comparative study of simulated and real spirometric results for different patient states (healthy lungs, restrictive lung disease, and obstructive lung disease of different localization and degree) was performed. The volume-flow curve and such standard parameters as FEV1, FEV1%VC, MEF75 etc. were analyzed.

A mathematical description of collapsing bronchi was proposed. All fundamental phenomena present during spirometry also appeared in VRS, especially characteristic dependence between lung volume and air flow for forced expiration. In particular, both airway resistance and the flow limitation were described with one formula derived from commonly known dependence of the resistance on lung volume. Generally there were no significant differences between simulated results and those seen in clinical practice. Only simulation of obstruction in upper airways gave incorrect results, which suggested a different flow limitation mechanism (perhaps wave-speed limitation).

Our VRS can already be used in medical education, e.g. courses of spirometry, and in some other applications. It seems that the significance of the wave-speed criterion has been overestimated.