Spirometry

SPIROMETRY, SPIROMETER (from Latin spiro- I breathe and Greek metron-measure). A spirometer is an instrument for measuring the quantity of air displaced by the human respiratory apparatus (see Breathing, respiratory apparatus); spirometry is part of complex anthropometric measurements. Spirometry determines: 1) vital capacity of the lungs, 2) respiratory air, 3) supplemental air, 4) reserve (backup) air (see Breathing, classification and composition of pulmonary air). After maximum exhalation, the so-called residual (remaining) air remains in the lungs, which cannot be measured spirometrically. The magnitude of spirometric data, showing significant individual variations, depends on height, weight, build, condition of the lungs, position of the diaphragm, condition of the endocrine glands, autonomic nervous system, as well as training of the respiratory muscles. Schnepf proposed the following table as a scheme for vital lung capacity in men per centimeter of height depending on age: Quantity Quantity Age of air Age of air in cm³ in cm³ Up to 6 years .... 4.50 From 16 to 18 years 20.65 From 6 to 8 years . 9.50 » 18 -» 20 » 23.40 » 8 » 10 » 11.40 » 20 » 25 » 23.25 » 10 » 12 » 12.00 » 25 » 30 » 22.98 » 12 » 14 » 14.17 » 40 » 50 » 21.00 » 14 » 16 » 16.44 In the opinion of the authors, spirometry has value for the functional diagnosis of the cardiovascular system; thus, in the literature collected by Romberg, it is indicated that with cardiac decompensation, the reserve air changes first; Engelhardt found that with compensated heart defects, vital capacity equals 70-100% of normal, with decompensated it decreases to 40%; the mentioned author proposed a special indicator of heart failure - the ratio between maximum respiratory air (respiratory + supplemental) and maximum respiratory rate. Engelhardt's experiments were conducted as follows: he made subjects breathe into a tube connected to a spirometer (capacity 15 l) until the appearance of pronounced asphyxia; in healthy subjects he found this indicator equal to 100 (e.g., 60), with cardiac insufficiency the indicator decreases to 30-24; Likhacheva, based on her observations, concluded that with healthy lungs, the size of vital capacity allows one to judge the function of the cardiovascular system; Peabody divides cardiac patients into 4 groups, where vital capacity decreases from 100% to 40% of normal, parallel to the severity of heart disease. With pulmonary tuberculosis, vital capacity decreases depending on the severity of the process to 65-55% of normal 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, balanced by two weights connected to it by a rope thrown over 2 pulleys; the subject exhales into the inner hollow cylinder through a rubber tube with a glass tip (5); the exhaled air lifts the hollow cylinder; the volume of exhaled air is measured by a scale attached to the side (3); 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 plug (4) or by turning the outlet cock. Another type of spirometer is the Verden spirometer; in this device, the exhaled air enters a system of leather bellows enclosed in a metal box; as the bellows expand, they drive a gear connected to a pointer indicating in liters the amount of air passing through the spirometer. The Verden spirometer is easily damaged and soon gives incorrect readings; requires frequent checking. The Fleischl spirometer-small water gas meters.