TH

HE PROGRESS of medicine is largely dependent upon the discovery of methods tending toward greater accuracy in diagnosis. Any clinical or laboratory test therefore, which tends toward greater diagnostic refinement is certain to find favor with the medical profession. In 1846 Mr. John Hutchinson (1) an English surgeon, brought forth a method which he believed would be of great assistance in the diagnosis of diseases of the respiratory system. He conducted extensive investigations on the respiratory function and brought into prominence many of the terms now commonly employed in connection with respiration. Upon one phase of the subject particularly did he concentrate much of his attention, namely, the quantity of air an individual is capable of expiring after the deepest possible inspiration. This quantity is known as the vital capacity. To the determination of the vital capacity, he attached considerable importance and believed it offered a

1 From the Medical Division of the University Hospital and the Department of Research Medicine, University of Pennsylvania.

This paper was awarded the College of Physicians' Prize offered to members of the Staff of the University of Pennsylvania.

ANNALS OF CLINICAL MEDICINE, VOL. III, NO. 4

means by which diseases of the respiratory organs could be detected.

Since Hutchinson's time, and especially in recent years, many other investigators have made studies on vital capacity both in health and in disease. Much has been written and many claims have been made for the vital capacity determination as an aid in diagnosis. From an analysis of the various papers on the subject in conjunction with our own application of the method to patients in the Medical Wards of the University Hospital, we have come to the conclusion that while the vital capacity determination possesses some diagnostic value, yet the procedure also possesses very definite limitations in clinical medicine. To point out these limitations, and to properly evaluate the vital capacity as a diagnostic procedure will be the purpose of this paper. To accomplish this object, we shall make use of whatever data may be available, whether original or published by other workers, regardless of whether the conclusions which they draw from the data presented, agree with ours or not.

It was early recognized by Hutchinson and may be accepted as generally true, that the vital capacity varies

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with the size of the individual. large person will usually possess large lungs or greater chest expansion, and therefore a larger vital capacity than a small person. Therefore, in attempting to predict what a person's vital capacity will be, the size of the individual must be taken into consideration. After a study of upwards of two thousand persons, Hutchinson derived a formula by means of which the theoretical vital capacity could be calculated from the height. Thus, there came into being the first socalled vital capacity capacity standard-a height standard. Modifications of this original standard have been suggested by numerous workers, while others have formulated

standards

based upon other body measurements, weight (2), chest volume (3), etc. The standard at present most widely in use that of West (4)-makes use of the height and weight. From these measurements, the surface area of the body is calculated by means of the formula of DuBois and DuBois: the resulting surface area in meters is multiplied by 25 in the case of males and 20 in females, giving the vital capacity in liters which a normal individual of that size is supposed to possess. Should the actual vital capacity as recorded by the spirometer be below this estimated figure, the subject is said to possess a low vital capacity. Since by many, a low vital capacity is regarded as indicative of some disease of the chest, it is important to inquire at this point to what extent low readings have been found to occur in normal persons.

Strangely enough very few data are available upon the range of variation

of vital capacity readings in heterogeneous groups of persons. Most of the reports available deal with groups of persons similar in age or race. Since these are factors which are known to influence the vital capacity, we can only reason by analogy concerning the variations which would be found to exist in a group representing all ages and races.

Since age appears to influence the vital capacity to a very great extent, let us first see what variations might be expected from this source alone. Hutchinson stated that from the thirtieth to the sixtieth years, there is generally a diminution in the vital capacity amounting to 1.43 cubic inches (23.4 cc.) for each year. Bowen (5), Myers and Cady (6), and Pratt (7), have more recently reported readings showing the marked diminution of vital capacity which accompanies advancing age, while Wilson and Edwards (8) have shown that in childhood the vital capacity is likewise well below standards for adults. Bowen presents a curve which would indicate that a man having a vital capacity of 5400 cc. at thirty years of age, might be expected to have approximately 54 per cent of this at the age of 85. If age is capable of producing reductions of such magnitude as this, it evidently outranks all other known factors reducing the vital capacity in normal persons. Differences of height and weight are of secondary importance. For example, a man of 5 feet 2 inches, weighing 100 pounds would, according to West's surface area standard have a vital capacity of only 1900 cc. less than a man of 6 feet 2 inches weighing 200

pounds, whereas the latter, according to Bowen, would lose approximately 2500 cc. between the ages of thirty and eighty-five. Any standard or formula therefore, failing to make an age correction, will necessarily give grossly erroneous results when applied to heterogeneous groups. It is true It is true that by the use of such a graph as that of Bowen, a correction can be made for certain ages, but it is also true that the effects of age manifest themselves earlier in some persons than others, so that while such a correction will be found helpful in the average case, yet it must be remembered that wide variations will frequently be found.

Obesity also is known to reduce the vital capacity. Hutchinson found that excess weight up to 7 per cent above the normal, exerts practically no effect upon the vital capacity, but that for the next 35 pounds every pound of additional weight may be expected to diminish the vital capacity by 1 cubic inch (16.38 cc.). Here again, the appropriate correction can readily be made, but Bowen (5) shows that the vital capacity diminution due to obesity is by no means as uniform as this formula would suggest. It therefore seems unwise to attempt to apply any uniform obesity correction. in all cases.

Race is known to exercise a marked influence upon the vital capacity: Foster and Hsieh (9) for example find that the Chinese give readings about 20 per cent below American standards. It seems probable that further studies will demonstrate similar variations in other races.

From the above facts it may therefore be assumed that in any heterogeneous group representing a true sampling of the world's inhabitants, wide variations in vital capacity would be found. Since the patients in the medical wards of our large city hospitals are drawn from all classes, nations and ages, one would therefore not expect to derive much diagnostic assistance from the use of any of our common vital capacity standards. This has been our experience at the University Hospital.

Let us now inquire regarding the value of vital capacity standards when applied to a group whose members differ relatively little as regards age and race. Plenty of observations upon such groups are available. For the purpose of this paper, we have selected Hewlett and Jackson's (10) study as being the most satisfactory. These authors have recorded among other measurements, the surface area and vital capacity in a group of 400 normal male students at Leland Stanford Jr. University, California. They have plotted a frequency graph and determined the standard deviation of the vital capacity readings which they obtained. These data were not exactly what our present purposes required, since we were less interested in the question of how much the readings might vary from one another than we were in the frequency and degree of variations from the estimated normal. We have therefore, from the recorded surface areas, estimated what each individual's vital capacity should be according to West's standard, and expressed the actual vital capacity readings in per