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.

Method for the measurement of the molar mass of gases or gas mixtures and an apparatus for the performance of the method

Measurement of functional residual capacity (FRC) during mechanical ventilation is important to standardise respiratory system compliance and adjust the ventilator settings to optimise lung recruitment. In the present study we compared three methods to measure FRC. The bias flow nitrogen washout technique (FRCN2MC), the multiple breath nitrogen washout (FRCMBNW) and the multiple breath sulphur-hexafluoride washout using the molar mass signal of an ultrasonic flow meter (FRCMBSF6) were compared in six adult monkeys after endotracheal intubation and during spontaneous breathing and mechanical ventilation at three different positive end-expiratory pressure (PEEP) levels of 0, 5 and 10 cmH2O. Animal research laboratory. We found good agreement between all three methods and they all accurately measured changes in FRC when PEEP was increased. The coefficients of variance of the three measurement techniques were in the same range (1.3–9.2%). The measurement of the tracer gas concentration with the molar mass signal of the ultrasonic flow meter provides a good and simple alternative to respiratory mass spectrometer for FRC measurements in ventilated subjects.

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Measurement of lung volume in mechanically ventilated monkeys with an ultrasonic flow meter and the nitrogen washout method

A method and device are provided for measuring state of lung function of a patient using ultrasonic flow and molar mass measurement. Flow and molar mass signals are recorded during tidal breathing without requiring patient cooperation. Statistical analysis of the recorded data in combination with anthropometirc data and/or data form a questionnaire can be used to diagnose various pulmonary ailments or diseases.

Method for non-cooperative lung function diagnosis using ultrasound

In the method proposed, the gas or gas mixture under analysis is passed through at least one support (5) in which at least one acoustic or ultrasonic transmitter or receiver cell (S1, S2) is located, preferably at an angle to the axis of the tube, to form a measurement path. The acoustic or ultrasonic transmitter or receiver elements (S1, S2) emit a pulsed acoustic signal, and the travel times of the pulses over the measurement path are determined. The variation in gas temperature along the at least one acoustic-transmission path is determined by, for instance, a temperature probe. The molecular weight is determined from the travel time of the acoustic pulses and the measured or assumed temperature. The device proposed is suitable for use in diagnosing deficiencies in the functioning of the lungs.

Method and device for determining the molecular weight of gases or gas mixtures

Statistical modelling of lung function from multiple-breath washout and complex tidal flow waveform data

We present the design of an ultrasonic respiration analysis system. The system determines the velocity of the respiratory gas flow by measuring absolute transit-times of ultrasonic pulse trains. Besides this standard flow meter function the system computes the 'equivalent molecular weight' M* of the gas flow: M* is calculated by combining the results of the ultrasonic transit-time measurements with temperature measurements along the sound transmission path. The gas composition dependent parameter M* can be used to determine additional respiratory parameters, e.g. functional dead space or total lung volume.

C. Buess

Papers

Ultrasonic Respiration Analysis