Chest

Chest

Volume 102, Issue 1, July 1992, Pages 139-142
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Effects of Body Position and Age on Membrane Diffusing Capacity and Pulmonary Capillary Blood Volume

https://doi.org/10.1378/chest.102.1.139Get rights and content

The effects of body position and age on the membrane diffusing capacity (Dm), pulmonary capillary blood volume (Vc), and the single breath carbon monoxide diffusing capacity (Dco) were evaluated in the erect (sitting) and supine positions in 16 normal young men (under 40 years old, younger group) and in 13 older men (over 40 years old, older group). Dm and Vc were estimated by several measurements of the Dco at increasing alveolar oxygen tension (PAO2). The results showed that Dco, Dm, Vc, and Kco (Dco corrected by alveolar volume) decreased with age in both positions. The differences in Dco, VC, and Kco between the two positions (supine minus the erect position) also decreased with age. The mechanisms of the increases in Dco in the supine position remain to be explained but may be due to a change in pulmonary capillary shape from an elliptical (erect position) to a circular configuration (supine position) since Vc increased more than Dm on assuming the supine position. The findings may be of clinical importance since many physicians have attempted to utilize a reduction in the positional change in Dco as a potential marker of disease. (Chest 1992; 102:139–42)

Section snippets

METHODS AND MATERIALS

Twenty-nine male adults were studied. Sixteen younger subjects (age under 40 years old, younger group) were professional employees of our hospital (students and residents), and 13 older subjects (age over 40 years old, older group) were selected from the patients who were admitted to the hospital previously for physical check-up. None had a history of cardiopulmonary disease and all denied respiratory symptoms such as cough or dyspnea. Their physical examination, chest roentgenogram,

RESULTS

The general data about the physical and functional characteristics of the 29 male subjects are given in Table 1. The younger group consisted of 16 male subjects with an age range from 22 to 39 years (mean ± SD, 28.1 ± 5.3 years). In the older group, there were 13 male subjects with an age range from 53 to 70 years (mean ± SD, 60.3 ± 5.3 years).

The values of Dco, Dm, Vc, Kco, and VA (alveolar volume) obtained in the erect and supine positions were significantly higher in younger group than in

DISCUSSION

Dco has been shown to decrease with age in adults.4, 5, 6, 7, 8 This has been attributed variously to changes in Dm and Vc. Our results confirmed the observation that Dco decreased with age. The influence of age on Dco could not be explained by the reduction of VA with age, because Kco also decreased with age.

The effect of age on the components of Dco, Dm, and Vc were studied less often. There were some controversies about the effect of age on Dm and Vc 7,9,10 In this study, Dm and Vc decreased

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Manuscript received July 15; revision accepted October 18.

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Copyright © 1992 The American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.