Abstract: The invention relates to an ultrasonic spirometer with a graduated tube where a transmitter/receiver cell pair is positioned in a graduated portion diagonally or perpendicularly to the graduated tube axis, with an easily replaceable breathing tube being insertable into the graduated tube. The breathing tube is at least partially made from essentially one material which is permeable for ultrasonic waves, but wholly or at least largely impermeable to germs and contaminants. In accordance with the invention, the material permeable for the ultrasonic waves and wholly or at least largely impermeable to the germs and contaminants is positioned at least in the area in which the graduated portion intersects the graduated tube over the whole circumference of the breathing tube.

Abstract: The invention relates to a method for the measurement of the molar mass of a gas or gas mixture and an apparatus for the performance of the method. The gas or gas mixture to be investigated is passed through at least one holder, on which at least one sonic or ultrasonic transmit-receive cell is arranged defining a baseline and preferably arranged obliquely to the axis of the tube. The sonic or ultrasonic transmit-receive elements radiate a pulsed sonic signal, which measures the transit times of the sonic pulses along the baseline. Using a temperature probe for instance the variations in gas temperature along the at least one sonic transmission path is determined. From the transit time of the sonic pulses and the measured or assumed temperature the molar mass is found. The apparatus in accordance with the invention may be employed with advantage in pulmonary function diagnostics.

Abstract: The invention relates to a spirometer, more particularly an ultrasonic spirometer, in the case of which a pair of cells, of which one is a transmitter cell and the other is a receiver cell, are arranged in a test section with an oblique or perpendicular alignment to the axis of the duct containing the test section. For this purpose in accordance with the invention a readily replaced duct, which if necessary is sterile, is inserted into the test duct. In order to design such an ultrasonic spirometer so that it may be employed for clinical purposes, it is necessary for it to be kept sterile in a simple fashion. For this purpose in accordance with the invention a sterile duct in inserted into the test duct with an accurate fit and at the transition between it and the test section it has test windows such that inserts are inserted into corresponding openings which are transparent for acoustic waves but substantially impermeable for microorganisms and dirt.