Criee C.P.,Hudson Respiratory Care |
Sorichter S.,University Hospital Freiburg |
Kardos P.,Respiratory and Sleep Medicine at Maingau Hospital |
Merget R.,Ruhr University Bochum |
And 9 more authors.
Respiratory Medicine | Year: 2011
Body plethysmography allows to assess functional residual capacity (FRCpleth) and specific airway resistance (sRaw) as primary measures. In combination with deep expirations and inspirations, total lung capacity (TLC) and residual volume (RV) can be determined. Airway resistance (Raw) is calculated as the ratio of sRaw to FRCpleth. Raw is a measure of airway obstruction and indicates the alveolar pressure needed to establish a flow rate of 1 L s-1. In contrast, sRaw can be interpreted as the work to be performed by volume displacement to establish this flow rate. These measures represent different functional aspects and should both be considered. The measurement relies on the fact that generation of airflow needs generation of pressure. Pressure generation means that a mass of air is compressed or decompressed relative to its equilibrium volume. This difference is called "shift volume". As the body box is sealed and has rigid walls, its free volume experiences the same, mirror image-like shift volume as the lung. This shift volume can be measured via the variation of box pressure. The relationship between shift volume and alveolar pressure is assessed in a shutter maneuver, by identifying mouth and alveolar pressure under zero-flow conditions. These variables are combined to obtain FRCpleth, sRaw and Raw. This presentation aims at providing the reader with a thorough and precise but non-technical understanding of the working principle of body plethysmography. It also aims at showing that this method yields significant additional information compared to spirometry and even bears a potential for further development. © 2011 Elsevier Ltd. All rights reserved.
Kohlhuber M.,Institute for Applied Research |
Luegmair M.,ISKO engineers AG
Acta Acustica united with Acustica | Year: 2012
High frequency transient wave propagation is a very interesting physical area. Currently, a large number of measurement methods are in use to qualify these signals. Typically, however, only the corresponding frequency domain spectra are computed and further investigated. Concerning the simulation of these signals there have been many attempts to approach real test signals. In many cases, however, it was only possible to calculate averaged spectra or low frequency time signals with an acceptable effort. In case of the application of crash impact sound sensing there is a need for simulating a high-frequency transient bending wave in the range from 5 to 20 kHz in the time domain. Thus, a simulation method based on the mathematical description of the main physical effects is developed (section 2). These formulas describe the wave propagation on its way through the structure. In order to get a good reproduction of propagation the infinite number of possible rays has to be reduced to only a few relevant rays (section 3). Here, the superposition of the single rays to the final time signal at the sensor position is also shown. In a further step the application of the simulation method for a typical car structure is shown and the good agreement between measurement and simulation is discussed (section 4). A short outlook on possible application areas (section 5) is followed by the conclusion (section 6). © S. Hirzel Verlag · EAA.