Air Transmission

Air transmission, introduced into physiology by Marey, is applied in recording many physiological phenomena, for example, respiratory movements, cardiac impulse, contractions of muscles, etc. The principle of air transmission is based on the fact that if in a closed system there are two places with flexible walls (rubber membranes), then pressing on one of them, due to the slight inertia of the air, immediately causes bulging of the other, and conversely, pulling one causes the other to sink. Usually, two metal boxes connected by a rubber tube are used - so-called Marey's drums (see Figure 1), one of which is the receiving one (see Figure 2) for changes in pressure (see Cardiograph, Pneumograph), and the other, equipped with a light straw lever that increases the amplitude of the rubber membrane, records all changes in pressure with the help of this lever (see Figure 3). The first drum is called the receiving one, the second - the recording or registering one. Air transmission, being one of the methods of graphical recording of phenomena, played an enormous role in the study of the activity of the heart, respiratory apparatus, and (to a lesser extent) the neuromuscular system. Air transmission works well if the pressure in the closed system (receiving capsule - rubber connecting tube - registering capsule) is equal to atmospheric pressure,

Figure 2. Receiving capsule - cardiograph.

which is achieved by using special valves, and if the rubber membranes are well stretched. Air transmission, even properly constructed, still cannot

Figure 3. Recording on a kymograph with air transmission. Cheyne-Stokes respiration.

ideally correctly transmit very slight or very rapid changes in pressure, since its material parts (rubber membranes, lever, air) possess (though slight) inertia.