Spirometry

SPIROMETRY, SPIROMETER (from Latin spiro—I blow, and Greek metron—measure). Spirometry is the measurement of the amount of air moved by the human respiratory apparatus (see Respiration, respiratory apparatus); spirometry is included in the complex of anthropometric measurements. Spirometry determines: 1) vital capacity of the lungs, 2) tidal air, 3) complemental air, 4) reserve (supplemental) air (see Respiration, classification and composition of pulmonary air). After maximal expiration, so-called residual air remains in the lungs, which is spirometrically immeasurable. The magnitude of spirometric data, while showing significant individual fluctuations, depends on height, weight, build, condition of the lungs, position of the diaphragm, state of the endocrine glands, the autonomic nervous system, and also on the training of the respiratory musculature. Schnepf proposed as a scheme the following table of vital capacity of the lungs in men per centimeter of height depending on age: Up to 6 years—4.50 cm³; 6 to 8 years—9.50 cm³; 8 to 10 years—11.40 cm³; 10 to 12 years—12.00 cm³; 12 to 14 years—14.17 cm³; 14 to 16 years—16.44 cm³; 16 to 18 years—20.65 cm³; 18 to 20 years—23.40 cm³; 20 to 25 years—23.25 cm³; 25 to 30 years—22.98 cm³; 40 to 50 years—21.00 cm³. According to the authors, spirometry is significant for the functional diagnostics of the cardiovascular system; thus, in literature collected by Romberg, it is indicated that in cardiac decompensation, it is primarily the reserve air that changes; Engelhardt found that vital capacity in compensated heart defects equals 70-100% of the norm, while in decompensated ones it decreases to 40%; the aforementioned author proposed a special indicator of heart failure—the ratio between maximal respiratory air (tidal + complemental) and maximal respiratory frequency. Engelhardt's experiments were conducted as follows: he forced subjects to breathe into a tube connected to a spirometer (with a capacity of 15 liters) until the appearance of sharply pronounced asphyxia; in healthy individuals, he found this indicator to be equal to 100, while in heart failure, the indicator decreases to 30-24; Likhacheva, on the basis of her observations, came to the conclusion that in the presence of healthy lungs, one can judge the function of the cardiovascular system by the magnitude of vital capacity; Peabody divides cardiac patients into 4 groups, where vital capacity decreases from 100% to 40% of the norm, parallel to the severity of the heart disease. In pulmonary tuberculosis, vital capacity decreases depending on the severity of the process to 65-55% of the norm and less.

Spirometer. The generally accepted Hutchinson spirometer (see figure) is a gasometer consisting of two cylinders, of which the outer one is filled with water to the upper edge; the inner one (1), inverted, is immersed in water and balanced by two weights connected to it by a cord passed over 2 pulleys; the subject exhales into the inner hollow cylinder through a rubber tube with a glass mouthpiece (5); the exhaled air lifts the hollow cylinder; the volume of exhaled air is measured on a scale attached to the side (3), and the scale indicator is usually calculated up to 6,000-7,000 cm³. After each test, the inner cylinder filled with exhaled air is emptied by opening a tightly fitted stopper (4) or by turning a discharge valve. Another type of spirometer is the Wreden spirometer; in this device, the exhaled air enters a system of leather bellows enclosed in a metal box; the bellows, upon inflation, actuate a gear connected to a needle that indicates in liters the amount of air passing through the spirometer. The Wreden spirometer breaks easily and soon gives incorrect readings; it requires frequent checking. The Fleischl spirometer is a small water-based gas meter.