Surgery – Truss – Pad
Patent
1995-04-12
1997-07-08
Cohen, Lee S.
Surgery
Truss
Pad
7386128, A61B 508
Patent
active
056450710
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for the measurement of the molecular mass of gases or mixtures of gases and to an apparatus for the performance of the method.
BACKGROUND OF THE INVENTION
For the determination of the composition of gases or gas mixtures mass spectrometers or gas specific sensors are generally employed. Mass spectrometers are complex instruments, which permit extremely accurate gas analysis. Sensors for measurement of the concentration of specific gases are on the contrary normally simpler devices, which calculate the concentration of a given gas on the basis of certain physical or chemical properties thereof, as for example an absorption line in its spectrum or a paramagnetic property of the gas.
SUMMARY OF THE INVENTION
One object of the invention is to determine the molecular mass of a gas or gas mixture in a free holder cross section, that is to say without any interference in the flow geometry.
In accordance with the invention this object is to be attained by passing the gas to be investigated through at least one holder, on which at least one sonic or, respectively, ultrasonic transmit and receive cell is arranged as a baseline and preferably obliquely to the tube axis. The sonic or, respectively, ultrasonic transmit and receive cells radiate a pulsed sonic signal. The transit times of the sonic pulses along the baseline are measured. The temperature may be estimated. Using at least one temperature probe it is however possible for the variations in gas temperature to be measured as well for at least one sonic transmission baseline. The molar mass is found from the transit time of the sonic pulses and from the temperature.
Ultrasonic sensors, as applied in the present invention, are generally known in the fields of ultrasonic spirometry in connection with another purpose. For instance in the Japanese patent publication 60-117149 A and the Swiss patent publication 669,463 A5 ultrasonic spirometers are disclosed, in the case of which a transmit-receive cell pair is arranged on a baseline obliquely in relation to the axis of the instrument's duct. In the case of such known ultrasonic spirometers the flow velocity is determined using ultrasonic transit time measurement.
This inherently known effect may in accordance with claim 8 be utilized in the method in accordance with the invention since the transit times of the sonic pulses are also employed for the calculation of the flow velocities of the gas or gas mixture, whose molar mass is determined. In this respect linearity errors in the computation of the flow velocity may be corrected in an advantageous fashion by using an electronic circuit at the output.
The above mentioned method in accordance with the invention may be more particularly used in pulmonary function diagnostics, since in this case both the results of the flow measurement and also those of continuous gas analysis are of interest.
In the case of pulmonary function diagnostics as so far practiced gas analyses have been performed by means of a plurality of sensors which are specific for the respective gas components. As a rule measurement by such sensors is in a shunted flow, that is to say part of the flow is branched off from the gas composition to be measured and subjected to measurement using such sensors. These known methods of measurement are complex and, owing to the necessary tapping of part of the gas flow, also lead to spurious results. By means of the method in accordance with the invention, pulmonary function analysis may be performed in real time and on-line. The measurements may then be performed using one ultrasonic sensor and only one additional sensor, something representing a saving in apparatus complexity. More particularly, it is possible for the method to be employed to determine the following parameters in a simple fashion:
The lung volume including FRC, the N.sub.2 wash-out curve or, respectively, the helium wash-in curve, the molar mass profile of the expiratory alveolar gas curve. Owing to the above mentioned combination
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Buess et al., "Design and Construction of a Pulsed Ultrasonic Air Flowmeter," IEEE Transactions on Biomedical Engineering, vol. BME-33(8), pp. 768-774. Aug. 1986.
Buess et al., "Ultrasonic Respiration Analysis," Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, vol. 13, No. 4, pp. 1597-1598. Oct. 1991.
Buess Christian
Guggenbuhl Walter
Harnoncourt Karl
Patzold Dieter
Cohen Lee S.
NDD Medizintechnik GmbH
Winakur Eric F.
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