High-frequency superposition means that the high-frequency signal is replaced by a low-frequency signal, and the two waveforms completely overlap. There is an instrument called a high-frequency superimposed normal-frequency jet ventilator. The high-frequency superimposed normal-frequency jet ventilator is a new type of ventilation equipment. The principle is to use a unique jet laryngoscope sheath to use both normal frequency and high frequency on the glottis at the same time. Frequent jet airflow ventilates the patient.