Body plethysmography – Its principles and clinical use

• Published in: Respiratory medicine Vol. 105; no. 7; pp. 959 - 971
• Main Authors: Criée, C.P, Sorichter, S, Smith, H.J, Kardos, P, Merget, R, Heise, D, Berdel, D, Köhler, D, Magnussen, H, Marek, W, Mitfessel, H, Rasche, K, Rolke, M, Worth, H, Jörres, R.A
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.07.2011; Elsevier; Elsevier Limited
• Subjects: Airway obstruction; Airway Obstruction - physiopathology; Airway resistance; Airway Resistance - physiology; Biological and medical sciences; Chronic obstructive pulmonary disease, asthma; Data processing; Functional residual capacity; Functional Residual Capacity - physiology; Humans; Intrathoracic gas volume; Lungs; Medical sciences; Plethysmography, Whole Body - instrumentation; Pneumology; Principles; Pulmonary/Respiratory; Specific airway resistance; Spirometry - instrumentation; Total Lung Capacity - physiology; Whole-body plethysmography; Intrathoracic gas volume; Airway resistance; Whole-body plethysmography; Airway obstruction; Functional residual capacity; Specific airway resistance; Respiratory disease; Exploration; Volume; Airways obstruction; Whole body; Plethysmography; Pneumology
• ISSN: 0954-6111; 1532-3064
• DOI: 10.1016/j.rmed.2011.02.006

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.