Thoraco-abdominal Perimetry for Partitioning of the Tidal Volume into Fractions due to Rib Cage Expansion and Diaphragmatic Descent

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Abstract
In 10 healthy males, respiratory variations in rib cage and abdominal circumferences were detected with mercury-in-rubber transducers. The volumes of respired air were measured by pneumotachography. The purpose was to divide quantitatively the tidal volume into fractions referable to rib cage expansion and to diaphragmatic descent (costal and abdominal breathing respectively). The main practical problem is to get the transducers properly scaled, the method of perimetry otherwise being easy to apply. For this purpose a manoeuvre producing deliberate variations in the partitioning of costal and abdominal breathing at different tidal volume levels proved satisfactory (the manoeuvre of variably combined costal and abdominal breathing). By calibrating the transducers in this way it was also possible to make fairly good estimates of the tidal volumes from the perimetric variations. The relation between changes in lung volumes and in circumferences was found to be approximately linear within a considerable range of tidal volumes. In the group investigated—under the condition of quiet respiration in the semirecumbent position—the fraction of abdominal breathing was found to be 0.64, on average.