Lung volumes, intrapulmonary gas mixing and gas exchange of the Korean
An attempt has been made in this investigation to determine normal pulmonary functions in a limited number of Korean subjects of various age and then compare with the data obtained in other countries. In addition, a special attention was also given to characterize the pattern of changes in various pulmonary functions as a function of age. All subjects under observation were free of pulmonary diseases as judged by physical examination as well as by roentgenography.
A. Total Lung Capacity and Its Subdivisions: 120 subjects (60 males and 60 females) consisting of various age groups were employed for the study. The vital capacity and its subdivisions were determined by spirometry and the residual volume by Rahn's "three breath method" in which the concentration of nitrogen was
determined by a Fry gas analyzer. Duplicate to triplicate measurements were taken from each subject. Results may be summarized as follows:
1. The residual volume(RV) increased linearly as a function of age. The regression equation was; RV (ml, BTPS) = 26.05 x age(yrs) + 368 for males and RV(ml, BTPS) = 18.9 x age(yrs) + 318 for females. This indicates that the residual volume increases more in males than in females, as they get older. However, when
the ratio of residual volume/total lung capacity was computed, the above difference between males and females was not evident.
2. The vital capacity and its subdivisions were, by virtue of their small physical characteristics, lowest in teen agers. However, when a comparison was made between middle age (30∼40 yrs) and old age (67∼70 yrs) groups, the former group showed higher values than the latter (P<0.05) despite the fact that their physical characteristics were quite similar.
3. In order to make a better comparison among subjects, various lung volumes per unit surface area were computed. The tidal volume increased progressively with advancing age in males while it decreased in females. In the old age group, females showed a significantly lower tidal volume than males (p<0.05). The vital capacity and the inspiratory capacity were greatest in the middle age group in both males and females. Although the expiratory reserve volume increased with advancing age in males, this trend was not apparent in females.
4. The ratio of inspiratory capacity/vital capacity decreased in males as a function of age while the ratio of expiratory reserve volume/vital capacity increased significantly. However, these ratios did not change significantly in females. The difference in these values between males and females of old age group was highly significant (p<0.05). These facts together with the finding that the tidal volume per unit surface area was smallest in females of old age group indicate that old females are breathing shallowly with a small functional residual capacity. This characteristic breathing pattern in old females may have developed as a result of constant compression of the chest, imposed by Korean women's costume which they have been wearing for many decades.
5. For each subject, the predicted value of vital capacity was computed by using various formulas developed by Baldwin et al for adult Americans, by Lyon and Turner for young Americans (below 20 yrs) and bu Kanekami for young Japanese. When the ratio of the predicted/the measured value was computed for each individual, it was found that these formulas may be applied to the Koreans. However, the Turner's formula for young females was not applicable.
B. Statistical Aspect of Vital Capacity: Although it was shown in studies outlined above that the vital capacity of the Korean adult may be predicted by using the Baldwin's formula. it was felt that a more large scale approach is perhaps needed to ascertain this conclusion. Hence, the vital capacity was determined by a vitalometer in 1,143 adult males whose ages ranged from 20 to 60 years. On the basis of this study, the vital capacity as a function of age, height, weight and body surface area was computed and then tabulated. In addition, the Baldwin's formula was applied to each subject and the computed predicted value was, subsequently, compared with the measured value. Although there existed certain variations among subjects, the grand mean of the ratio of the predicted/the measured value was 97.6%, again supporting the earlier contention that the Baldwin's formula may be safely applied to the Koreans in clinical practice.
C. Intrapulmonary Gab Mixing: In 88 subjects whose ages varied from 9 to 82 years old, an index of intrapulmonary gas mixing was determined by measuring "pulmonary N^^2 emptying rate" as developed by Cournand. Each subject breathed pure oxygen for
7 minutes in order to wash out nitrogen from the lung. At the end of 7 minute period, an alveolar gas sample was obtained and was analyzed by a Fry gas analyzer for nitrogen. Duplicate to triplicate measurements were taken and the lowest value was used. The concentration of nitrogen in the alveolar gas at the end of 7 minute period (F^^AN2) was only 1.63% in subjects below 19 years old and increased progressively as the age increased. As a whole, F^^AN2 increased very gradually until 50 years of age after which it increased rather sharply. The highest value was 6.35% in a subject of 68 years. These indicate that the intrapulmonary gas
mixing is rather homogeneous until 50 gears of age, although the residual volume has increased markedly at this age. However, in subjects older than 50 years, the intrapulmonary gas mixing is quite uneven, which may reflect the development of physiological emphysema.
D. Pulmonary Gas Exchange: In 120 subjects who were employed for the measurements of total lung capacity and its subdivisions, the oxygen uptake(V^^O2) and CO^^2 output(V^^CO2) were determined and the alveolar gas exchange ratio was computed. Each subject, quietly lying on a bed, breathed air for a period of 15 minutes and the expired gas was collected during the later 10 minutes. The expired gas samples were analyzed for O^^2 and CO^^2 by a Scholander micro gas analyzer V^^O2 was also checked by spirometry. Both V^^O2 and CO^^2 were highest in middle age group and were lowest in teen agers. However, when these values were corrected for the difference in the body suface area, they were highest in teen agers and decreased with advancing age. The pulmonary gas exchange ratio remained unchanged and was in
the order of 0.80 in all groups. The ventilation equivalent wart equally lower in teen agers and middle age groups than old age group, suggesting a poor efficiency of gas exchange in the latter. However, the ventilation equivalent in females was
not different among three age groups.