Ventilation with rigid bronchoscopes. Evaluation of resistance by pressure drop by a proposed international standard

The ISO 8600-2-1 draft standard concerns measuring methods for ventilation properties in rigid bronchoscopes. Two lung models were designed in accordance with this draft, one for conventional ventilation, and the other for jet-ventilation (venturi ventilation). Lung model I: An air supply was connected to a 4 liter container. The test object (bronchoscope) was exposed to air flowing out of the container through the bronchoscope, and the pressure in the container was recorded. The flow velocities were 20-60 l.min-1. Lung model II: A pressure gauge was connected to a 2 liter container. The test object was introduced into the container through an gastight opening. A pressure gas injector was connected to either the instrument port or the ventilation port of the bronchoscope. The injected pressures were 100-500 kPa.

Study I. The pressure drop increased exponentially with increasing air flow. It also increased rapidly with decreasing diameter of the bronchoscope. Study II. The pressure in small bronchoscopes increased very fast with increasing injection pressure. Dangerous pressures (above 50 cmH2O) were reached already at 2 kg.cm-2 with the smallest bronchoscopes. We suggest that the results should be given as "pressure drop" and not as "resistance".