Abstract:
Objective: Measuring pulmonary diffusing capacity （D
L）, alveolar capillary membrane diffusing capacity （Dm） and pulmonary capillary blood volume （Vc） in normal adults; calculating the regression equation correlated to age, height and body weight; evaluating the effect of age on Dm and Vc; studying the relationship among D
L, Dm and Vc.
Methods:Spirometry was performed in the sit position. Several measurements of diffusint capacity of the lung for carbon monoxide （D
L CO） were taken by single-breath method at increasing alveolar oxygen tension （P
A O
2）. The estimations of Dm and Vc were done by the method of Roughton and Forster.
Results:（1）There was a significant negative corelation between age and D
LCO, Dm and Vc. The correlations between D
L and Dm, Vc as well as V
A and D
L, Dm, Vc are significantly positive.（2）D
L and Dm decreased after 40 and Vc decreased after 50. D
L/V
A Dm/V
A and Vc/V
A decrease after 60 years of age. There was no significant difference of Dm/Vc among groups. （3）Height and/or age were the main variables in stepwise multiple linear regression equations for D
L, Dm AND Vc in all groups.
Conclusion:（1）There is a significant negative correlation between age and D
L, Dm and Vc.（2）D
L and Dm decrease after 40 and Vc decrease after 50. Age has not a significant influnce on Dm/Vc.（3）The declining in D
L may be due to the decrease of Dm and Vc. （4）The decrease of Dm may be related to the reduction of V
A with age. （5）Height and/or age are the main variables in regression equations for D
L, Dm and Vc.
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