What factors explain racial differences in lung volumes?

Abstract

In order to examine the physical characteristics that may determine racial differences in lung volumes, we studied healthy, nonsmoking Caucasian, Chinese and Indian males of similar ages (range 18-51 yrs). We measured spirometric function, flow volume curves, lung volumes, inspiratory and expiratory muscle pressures, alveolar distensibility and diffusing capacity, together with height, weight and fat free mass. Chest shape was measured using radiographs. The mean total lung capacity and vital capacity in the Caucasian group, expressed as percentage predicted, were 5 and 10% higher than in the Chinese group and 17 and 20% higher than in the Indian group. Chinese values for these measurements were 12 and 10% greater than Indian. We found that Caucasians had higher fat free masses, higher inspiratory and expiratory muscle pressures and wider chests than the other races. The Caucasians and Chinese had longer chests than the Indians. There was no difference in alveolar distensibility or in the diffusion coefficient between the groups. These findings suggest that Caucasians have larger lung volumes than Chinese and Indians because they have increased numbers of alveoli and physically larger chest cavities, and not because of greater alveolar distensibility. Chest dimensions, together with height and race explained 90% of the variation in forced vital capacity and 86% of the variation in total lung capacity. Height multiplied by fat free mass, a "physique factor", previously suggested as the best predictive factor for forced vital capacity in Caucasians, did not account for much of the variation in forced vital capacity between Caucasians and Indians, presumably because it takes no account of differences in chest dimensions.

The large lungs of elite swimmers: an increased alveolar number?

“…However, if this effect alone accounted for swimmers' larger VC one would not anticipate an increase in the FRC seen in our swimmers, which is consistent with the possibility that swim training per se enhances lung growth. A previous study from this laboratory showed that Caucasians with higher values for MIPRv had values for alveolar distensibility similar to Indians and Chinese subjects with lower values for MIP RV [31]. This implies that an increased ability to distend the thoracic cage does not necessarily lead to an increased distensibility of the alveoli.…”

“…adaptation alone. In a recent study [31], we reported lung volumes and chest dimensions in Chinese men closely approximating Caucasian values, and speculated that the next generation of Chinese will have similar lung capacities to Caucasians, probably as a result of better nutrition and more exercise.…”

“…There was also a highly significant correlation between chest surface area and VC at all lung volumes. In this regard, the increased TLC found in Caucasians as opposed to Indians has been found to be related to the longer and wider chests of Caucasians [31]. The exact mechanism which causes growth of the chest wall is unknown, though it is clear that swimmers have a larger chest surface area to accompany their larger lungs.…”

“…In the present study, there was no significant difference in alveolar distensibility between swimmers, runners and controls, suggesting either: 1) alveolar multiplication and not hypertrophy as the growth mechanism to account for the larger lungs of swimmers; 2) alveolar hypertrophy, not detectable through the measurement of pulmonary distensibility; or 3) the swimmers were endowed with the potential for a high number of alveoli from early childhood, enabling them to develop big lungs, although we think this proposal is less likely. Detailed discussion on the relationship between chest size, alveolar distensibility, and alveolar size and number is covered in an earlier publication [31].…”

Interpretation of Spirometry: Selection of Predicted Values and Defining Abnormality

“…45 The difficulty in establishing the magnitude of differences between Caucasians and Africans or Asians accurately notwithstanding, it is certain that ethnicity is a major determinant of lung function. 46 Therefore, it is now a standard practice to develop separate equations for multi-ethnic populations. The most widely used equations in the United States are based on the NHANES III data.…”