Apparatus for the determination of respiratory passageway resistance

Claim 1

In an apparatus for determining respiratory passageway resistance, including a flow tube having a passageway including a flow resistance with means for varying the resistance value periodically at a frequency lying above the breathing frequency, measuring means for supplying a measurement signal which varies in accordance with a parameter of the flow in the flow tube, the improvement comprising: said flow resistance comprising a single fixed resistance extending across the passageway of said flow tube and having a flow surface determining a basic resistance value R o ; and sinusoidally variable shutter means as resistance value varying means associated with said flow surface of said single fixed resistance for the periodic, substantially sinusoidal superposition of resistance variations r onto said basic resistance value; said measuring means comprising flow measuring means connected to said flow tube and having first and second measurement passageways connected to the output of said flow measuring means, a first frequency filter in said first measurement passageway, a second frequency filter in said second measurement passageway, said first frequency filter having a frequency characteristic for ascertaining flow components V o due to low frequency breathing, and the second frequency filter having a frequency characteristic for ascertaining flow components v due to the higher frequency resistance variations caused by said shutter means, and further comprising circuit means connected to the outputs of said first and second measurement passageways to provide the respiratory passageway resistance R aw from the lower and higher frequency flow components V o and v obtained from said measurement passageways, and from the resistance values R o and r in accordance with the relationship ##EQU11##