According to the indices of pulmonary function tests and etiology, pulmonary function is divided into obstructive ventilation dysfunction and restrictive ventilation dysfunction. Obstructive ventilatory dysfunction is defined as narrowing or obstruction of the airway, which increases airway resistance and thus limits alveolar hypoventilation. The obstructive ones are dominated by reduced flow rate indicators, such as FEV1/FVC, and are mainly seen in chronic obstructive pulmonary disease and bronchial asthma. Restrictive is the restriction of alveolar expansion during inspiration, causing alveolar hypoventilation, mainly by the reduction of lung volume, such as spirometry, and is mostly seen in diseases such as interstitial pulmonary fibrosis, thoracic deformity, and pleural effusion. However, sometimes severe obstructive ventilatory dysfunction can be accompanied by partially restrictive features, i.e., a decrease in both expiratory flow and lung volume, and a mixed ventilatory dysfunction is formed.