Measurement of gas free body volume by a diving device.

A device is presented for determination of gas free body volume, by which total body volume as well as lung volume together with intestinal gas can be measured. The measurement is performed under water. The subject to be measured keeps his head in an airfilled cylinder which allows free breathing during the measurement procedure under water. The subject sits on a seat which is connected with a vertical "probe" that is submerged in a water basin. This "body density probe" carries several measuring rods of different diameter on its upper end, which lead to an increase of buoyancy when sinking deeper into the water after additional weights have been put on the device. These rods lead to new equilibrium states which are also dependent on the compressable gas volume attached to the probe. Three equilibrium states with different added weights give a physical definition of gas free body volume, which can be calculated from a number of accurately measurable single items.