Elsevier

Respiratory Medicine

Volume 105, Issue 7, July 2011, Pages 959-971
Respiratory Medicine

Review
Body plethysmography – Its principles and clinical use

https://doi.org/10.1016/j.rmed.2011.02.006Get rights and content
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Summary

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.

Keywords

Whole-body plethysmography
Intrathoracic gas volume
Functional residual capacity
Specific airway resistance
Airway resistance
Airway obstruction

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This article is dedicated to the memory of the co-author Priv. Doz. Dr. Wolfgang Marek who died in October 2010. He was a passionate researcher and teacher and particularly engaged in the better implementation of physiological insight into clinical practice.