2018 年 13 巻 4 号 p. JFST0023
Since gas exchange in the human lung is mass transports by fluids, respiratory physiology should be based on fluid dynamics. However, current theories of respiratory physiology have been established by regarding the respiratory system as an analogy of electric circuit where the airflow is assumed laminar, and led clinicians to wrong ways. In this paper, two representative cases are introduced. One is a popular pulmonary function test and the other is an artificial ventilation method for severe respiratory failure. Maximum forced expiration test is used for diagnosis of expiratory airflow limitation such as emphysema or chronic obstructive pulmonary disease (COPD). Although the cause of expiratory airflow limitation has been believed to be due to small airway obstruction, its true cause is the collapse of the intra-thoracic large airway. The mechanism of high-frequency ventilation (HFV), one of artificial ventilations with tiny tidal volume, has been believed that high frequency oscillation augments gas dispersion and improves gas exchange in spite of tiny tidal volume. However, recent clinical studies have revealed that HFV is useless for acute respiratory distress syndrome (ARDS) in adults. The true gas transport mechanism with tiny tidal volume is asymmetric airflow profile between inspiration and expiration due to the presence of bronchial bifurcations. In both cases, there are several papers published in famous journals more than 25 years ago, which stated the true mechanisms but currently have been seldom refereed. Reconstruction of respiratory physiology is an urgent task both for medical and engineering researchers.