구획모델에 기반하는 폐의 기능적 잔기용량 계측기법

Measurement of Functional Residual Capacity Based on Compartmental Model

The present study confirmed through experiment the superiority of new functional residual capacity (FRC) measuring techniques using a compartmental model to the existing technique in measurement characteristics. Assuming through deductive inference from a known compartmental model that the inspiration and‐expiration process is a constant air flow and the initial N2 concentration in the lung at the moment of measuring by N2 washout is known, we took the pulmonary ventilation system as the compartmental model. Because the compartmental model is a mathematical model explaining the variation of N2 ratio(FE) at the end of expiration with given FRC size, initial N2 concentration of FRC, and average air flow, reversely we can obtain FRC from the model if the initial N2 concentration of FRC and the average air flow are given and the variation of FE can be quantified. In order to test the validity of these measuring methods, we should have experimented with a subject, but because the subject’s absolute FRC could not be measured, we used syringe apparatus similar to a subject’s breathing only through the mouth and showing exact internal capacity(FRC). Experiment was conducted with the internal capacity of the syringe set at 0.1[L], 0.6[L], 1.1[L], 1.6[L], 2.1[L], and 2.6[L], respectively. The internal capacity of syringe was measured by the methods using FE and average air flow, which are necessary for the new methods, and by the existing method using expiratory air capacity and the N2 concentration in the expiratory air bag. When the result of estimating the internal capacity of syringe was analyzed in each experiment, the correlation efficient between the reference value(initially set FRC) and the estimated value was 0.9629 in the existing method, and 0.9956 in the new method. The standard deviation of absolute error was ±0.262[L] in the existing method, and ±0.087[L] in the new methods above. The present study confirmed through syringe experiment that, in N2 washout, the new FRC measuring techniques are more accurate than the existing method. It is considered necessary to test the validity of the measuring techniques devised in this study through additional clinical experiments.