[Effects of high frequency jet ventilation on respiratory airflow and gas exchange in dogs with inhalation injury].

Objective: The experiment was to investigate the effects of respiratory airflow on gas exchange.

Method: Eight healthy dogs were anesthetized with thiopentone. A 3-D partial dynamic analyzer was used to determine the inspiratory and expiratory flow velocity, and arterial blood samples were collected for blood-gas analysis during spontaneous respiration. Intravenous muscle relaxant was given quickly and the animals were kept apneic and then vapor (105 degrees C) was inhaled for 5 seconds. HFJV was carried out at random under 5 different conditions, each for 20 minutes. Changes in inspiratory velocity (Vi), expiratory velocity (Ve), Reynole's number, PaCO2, PaO2, and PIP were observed.

Result: 1. During spontaneous respiration, airflow was in form of laminar flow when Re < 1000, and expiratory airflow was either laminar or turbulent when 1000 < Re < 1500. 2. During HFJV, both expiratory and inspiratory airflow were turbulent when Re > 1500. 3. The expiratory velocity with HFTJV increased significantly (P < 0.05). PaCO2 decreased significantly (P < 0.05) compared with HFJV. Obvious negative correlation was found between them (r = -0.9216, P < 0.05), meanwhile inspiratory velocity had an increasing tendency.

Conclusion: 1. HFJV could maintain normal ventilation of dogs with inhalation injury. The mechanism might be associated with turbulent flow. 2. On the basis of HFJV, HFTJV increases inverse jet airflow, thus the respiratory airflow velocity may be increased and CO2 elimination improved.