This enables a measure of the total lung volume, and hence the residual capacity, which is difficult to measure. V A variant uses a piston to produce cyclical changes in the volume of a sealed chamber. For a given displacement volume, the pressure fluctuations depend on the volume of air in the chamber, i.e. the volume of the empty chamber minus the volume of the body. This enables higher frequency signals, reducing drift problems in pressure transducers. It is mainly used to estimate average body density, and hence fat content.
High sensitivity requires minimising volume consistent with patient comfort.
The Bod Pod Residual Volume Measurement by dilution. The reduction in concentration indicates the residual volume. Carbon dioxide and water vapour must be removed and oxygen added to keep the volume constant. Detailed procedure Record patient data, seat patient, apply nose clip, and attach to spirometer. Patient breaths, and oxygen flow is adjusted to remove any trend in volume.