A PREDICTION EQUATIONS FOR PULMONARY DIFFUSING CAPACITY FOR NITRIC OXIDE IN HEALTHY AFRICAN-AMERICAN ADULTS
Abstract
Pulmonary diffusing capacity for nitric oxide (DLNO) is a relatively new pulmonary function test to assess gas transfer in the lung. To date, there are no prediction equations made for healthy adult African-American (black) subjects. Thus, the purpose of this study was to create prediction equations for DLNO in this ethnic/racial group. A total of 59 healthy subjects (27 males and 32 females) were recruited to perform pulmonary function testing at Georgia State University. They were diverse in age (18-67 yr), height (140-189 cm), and body mass index (17.2-32.3 kg/m2). All subjects completed single-breath maneuvers at rest inhaling 43 ± 4 ppm NO with a standard diffusion mixture. The breath-hold duration was 5.6 ± 0.6 s. Multiple linear regression predicted DLNO based on the subject’s age, height, and sex. The prediction equation for DLNO (mL/min/mmHg) = 0.92·(height in cm) +38.8·(sex) – 0.012·(age2) – 25, where 1 = male, 0 = female for sex. About 77% of the variance in DLNO was accounted for by sex (67%), age2 (7%), and height (4%). The standard error of the estimate in predicting DLNO was 16.3 mL/min/mmHg. Those with higher resting heart rates had a lower DLNO (r =-0.28, p = 0.03) but it was not included in the regression model as it did not enhance the fit. Black males had a 7-10% lower DLNO and black females had a 12-15% lower DLNO compared to matched white subjects. Black males of the same age and height had a 10% smaller alveolar volume, while black females had a 15% lower alveolar volume compared to matched white subjects. In conclusion, DLNO values and alveolar volumes are reduced in blacks compared to matched whites. The regression model presented best predicts DLNO in African-Americans below 40 years of age.