Water-sealed spirometer

The water-sealed spirometer was the traditional device used to measure the volume of air moved in respiration. The Latin word spirare means to breathe. The most popular type of spirometer consists of a hollow cylinder closed at one end, inverted and suspended in an annular space filled with water to... 

Gas volumes may be measured directly by using one of several volume displacement spirometers. The simplest and oldest design, the water-sealed spirometer, uses a hollow cylinder, or bell, which is inverted and lowered into a bucket of water containing a tube for the movement of gas (Fig. 21.4). The bell rises or lowers as gas moves into or out of the gas space trapped between the bell and the... 

FIGURE 21.4 Schematic drawing of the water-sealed spirometer. The kymograph rotates at a constant speed, allowing for the inscription of a volume (y axis) versus time (x axis) plot as the bell moves up and down in response to gas movement at the outlet. 

A similar approach is used in the dry-seal spirometer. In this case, the bell is sealed to its base with a thin layer of latex (or some other thin and flexible material). As gas is introduced into the bell, the latex prevents its escape and forces the bell to move, as with the water-sealed spirometer. Dry-seal spirometers may be mounted horizontally, and may employ a moving piston instead of a moving bell. Manual and electrical recording are achieved as in the water-sealed spirometer. A diird type of volume displacement spirometer, somewhat less common recently, is the bellows, or wedge, spirometer. In this device, the gas to be measured is contained within a bellows whose expansion is recorded via a pen or a rotational potentiometer. 

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