[Flow dynamic studies of artificial tracheal tubes with speech valves]

A system is described for the high-accuracy measurement of the flow resistance of tracheostomy tubes without and with speaking valves during the phase of inspiration with regard to different conditions up to flows of 78 l/min. A microprocessor is employed for the acquisition of the signals and for the presentation of the results by means of a plotter. The results show that the flow resistance of tracheostomy tubes with two speaking valves of different construction in vertical position does not exceed the critical value of 5 mbar.s/l. Lateral tilting does not affect the flow resistance, whereas frontal tilting yields an increase in flow resistance.