Body mass, fat percentage, and fat free mass as reference variables for lung function: effects on terms for age and sex

摘要

BACKGROUND—Sexspecific cross sectional reference values for lung function indicesusually employ a linear model with terms for age and stature. Theeffects of also matching for body mass index (BMI= mass/stature2) or its components, fat percentage of bodymass (fat%) and fat free mass index (FFMI = fat freemass/stature2) were studied.
METHODS—The subjectswere 458 asymptomatic male and female non-smokers (383 men) and 22 female ex-smokers. Measurements were made of ventilatory capacity, lungvolumes, transfer factor (diffusing capacity, single breath CO method),and body composition (skinfold method). Linear and proportionalregression models were used.
RESULTS—Terms forfat% and FFMI significantly improved the accuracy of reference valuesfor all the primary lung function indices. The improvements in subjectswith atypical physiques (fat% and FFMI at the ends of thedistributions for the subjects) were in the range 0.3-2.3 SD comparedwith conventional regression equations. The new partial regressioncoefficients on age were independent of age related changes in bodyfat. The coefficient for total lung capacity (TLC) on age in men wasnow positive. Most differences between the sexes were eliminated. Aterm for BMI improved the descriptions of subdivisions of TLC butlacked the other advantages.
CONCLUSION—Allowancefor fat% and FFMI increases the accuracy of reference equations forlung function, particularly for subjects with a lot of fat and littlemuscle or vice versa. Allowance for BMI is less informative.