Vital Capacity of the Lungs

Vital Capacity of the Lungs, the maximum volume of air that can be exhaled after a maximum inhalation. In different people, the V.C.L. varies. On average, in men it is 3,500-4,000 cm³, in women 2,500-3,000 cm³, but in some individuals it can reach 6,000 cm³ or more. The volume of the so-called respiratory air, that is, the air that a person inhales and exhales each time during even, calm breathing, averages 500 cm³. It increases significantly during muscular work or with insufficient heart activity, and during the most severe shortness of breath, a person begins to use the entire V.C.L. The first systematic study of V.C.L. belongs to Hutchinson (1846). For quick and sufficiently accurate determination of V.C.L., he built his spirometer, which is still used almost unchanged today. When measuring V.C.L., the subject is asked to inhale the maximum amount of air and then exhale into the spirometer all the air they are capable of exhaling. During determination, three trials are made and the maximum figure is taken. Hutchinson examined about 3,000 healthy and sick people. He established that for a given person, the size of V.C.L. is more or less constant. It depends on the height, weight, and age of the subject. Some diseases significantly reduce V.C.L. Currently, the determination of V.C.L. is widely used as a medical control method in physical education to determine the degree of physical development, as well as in clinical research as a functional test of the lungs. The ratio of V.C.L. to body weight _r is called the vital index. In an adult man, this index should not be below 60. This number expresses the amount (cm³) of vital capacity (of the oxygen in the air) per 1 kg of weight. This value fluctuates depending on various favorable and unfavorable moments and has significance in medical control. In recent years, numerous researchers have tried to correlate V.C.L. with height, weight, body surface, chest circumference, and sitting height (height minus leg length). Myers provides tables from which it is easy to find standard values for normal V.C.L. depending on the above values. At the same time, he recommends first finding standard values and deviations from them for a given subject depending on weight, body surface, and height. Only in case of discrepancies between the obtained figures and the V.C.L. determined for this person should the found value be compared with standards calculated for chest circumference and sitting height, since these anthropometric values correlate less with vital lung capacity than the first three. Myers suggests denoting deviations from normal standards as a percentage of the norm for a given person, taken as 100. This conclusion is fully confirmed by numerous studies by Russian doctors working on medical control in physical education. V.C.L. changes significantly with age. Therefore, special standard tables have been compiled for growing children, by which the observed deviations from normal can be calculated with greater or lesser accuracy. For individual individuals, maximum figures for vital lung capacity are obtained at about 30 years of age. Starting from the age of 45, V.C.L. gradually decreases, falling by 60 years to 60% of normal. However, according to observations by Myers and Koby, individuals who lead an active lifestyle and have retained their working capacity show less decrease in V.C.L. with age. According to Dreyer, race and nationality noticeably influence the average figures for V.C.L. For example, when examining a group of Chinese, their V.C.L. was found to be less than that of Europeans. V.C.L. in women is always, as a rule, less than in men. Therefore, separate standard tables have been compiled for both sexes. Many physical exercises, for example, rowing and swimming, as well as breathing training, have a very large influence on the size of V.C.L. Usually, in people engaged in heavy physical labor, athletes, musicians who play wind instruments for a long time, and singers, very large V.C.L. is found upon examination. However, large V.C.L. is sometimes found in people on whom activities could not have any influence in this regard. This group includes people with an elongated chest cavity and a low diaphragm. A person's profession also strongly influences V.C.L. Dreyer divides all people in this respect into 3 classes. In class A, with the largest V.C.L., are sailors, military personnel, athletes and sportsmen, stokers, blacksmiths, boilermakers and other professions requiring heavy physical labor. To class B, with V.C.L. on average 8.7% less, he assigns merchants, railway workers, doctors, mechanics and higher-grade employees. Finally, to class C, whose average V.C.L. is 14.6% lower than in class A, Dreyer assigns tailors, shoemakers, painters, saddlers and lower-grade employees. However, people who engage in sports outdoors a lot, according to Dreyer, can be assigned to group A, regardless of their profession. Of course, one must always remember that in each individual case there may be deviations from average figures, since not all people of one profession or another have equally low or high vital lung capacity. For a physician, the influence of disease on V.C.L. may be most interesting. At the time Hutchinson began his observations, the physician had no X-rays, serological tests, or many other modern methods for examining patients. Therefore, Hutchinson saw in the study of V.C.L. valuable help in diagnosis. Dreyer points out that if the V.C.L. of a given subject is 10% less than the V.C.L. of his class, then it is probable that this subject is not quite healthy. If, however, the V.C.L. of the subject is 15% below the standard, then practically certainly his heart or lungs are unhealthy. A decrease in V.C.L. may depend on previously suffered diseases and on the pathological condition at the time of examination. In the first case, the causes may be: old pleural adhesions, deformation of the chest, ossification of costal cartilage, as well as disorders of the respiratory motor apparatus. The following diseases decrease V.C.L. during the course of the disease itself: organic heart diseases, hyperthyroidism, asthma, emphysema, bronchitis, pleurisy, pneumothorax, lung abscess, new formations in the chest cavity, pneumonia and pulmonary tbc. According to many authors, heart diseases decrease V.C.L. The more severe the patient's condition at a given time, the more V.C.L. is decreased. With the establishment of compensation and with successful treatment, V.C.L. again increases. The average figures for V.C.L. for a group of cardiac patients are always lower than the average figures for a group of healthy people. In pneumonia, V.C.L. is very strongly decreased. The lowest figures are obtained in days close to the crisis. With recovery, there is a gradual return of V.C.L. to normal. With complications, the return of V.C.L. to normal is delayed. Myers indicates that one should not allow a patient to begin his usual activities until V.C.L. has been restored to 90 percent of normal. In pulmonary tbc, V.C.L. is always definitely less than it should be according to the patient's weight, height, body surface, age and professional class. Improvement in clinical condition is always accompanied by an increase in V.C.L. With progressive development of the disease, V.C.L. continues to decrease. As for the causes causing a decrease in V.C.L., in heart diseases V.C.L. decreases due to blood stasis and expansion of lung capillaries, which should change the stretchability and elasticity of the walls of the pulmonary alveoli. In the initial stages of tbc, there is an increase in residual air in the lungs, and in more severe cases, the destruction of lung tissue undoubtedly significantly affects the decrease in V.C.L. Currently, with the development of preventive medicine, determinations of V.C.L. along with other, more perfect methods are being introduced into general use in different countries for the purpose of detecting the initial stages of heart and lung diseases. The method of determination itself is so simple that it can be applied just as easily as the determination of height and weight. However, certain precautions must be observed during measurements and the instruments must be checked.