A theoretical analysis of the barometric method for measurement of tidal volume.

The barometric method is unique in allowing measurement of tidal volume in a manner that requires no tactile contact with the subject. The equations used by previous investigators to calculate tidal volume described only events occurring during inspiration. Neglect of events during expiration caused a systematic error. Additional equations needed to calculate tidal volume for the barometric method are derived. An error sensitivity analysis is performed to assess quantitatively the accuracy of the calculated tidal volume due to propagation of errors in the experimentally measured variables. Numberical evaluation for typical cases indicates that the limit of accuracy for tidal volume measurement lies between 10 and 15%.