Diffusing Capacity of the Lung for Carbon Monoxide in Mexican/Latino Children. Quality Control and Reference Values

Single-breath diffusing capacity of the lung for carbon monoxide (Dl_COsb) values are used to evaluate gas exchange; however, the quality of maneuvers performed by children has not been evaluated, and reference values for young people living at moderate altitudes are not well established.

Our objectives were 1) to determine whether Dl_COsb maneuvers performed by a pediatric population would meet 2017 European Respiratory Society/American Thoracic Society (ERS/ATS) quality control standards; and 2) to report normal Dl_COsb values for Mexican/Latino children and adolescents living at moderate altitudes.

This study involved healthy young people 4-20 years of age from the metropolitan area of Mexico City (2,240 m above sea level) who were recruited in schools from July 2014 to August 2017. Dl_COsb testing was performed according to the 2005 ATS/ERS standards, and the quality control of each maneuver was analyzed according to the 2017 ERS/ATS standards. We constructed models for Dl_COsb with linear and quadratic terms for weight, height, and age as independent variables using shrinkage statistics, variance inflation factors, the Akaike information criterion, and R² to compare the results of different models.

Results were obtained for 420 individuals (53% boys) with a mean age of 11.7 ± 4.5 standard deviation (SD) years; 47% of maneuvers from children age 4-6 years were grade A (13% grade B), and 90% of those in children older than 13 years were grade A or B. Forty-six percent of the subjects had a Dl_COsb repeatability of <1 ml/min/mm Hg. The mean Dl_COsb was higher for boys than for girls (32.4 ± 13.6 [SD] vs. 24.1 ± 7.5 ml/min/mm Hg, respectively). The reference equation for boys was Dl_COsb = exp(1.63469 + [0.03251 × age] + [0.00846 × height] + [0.00304 × weight]), R² = 0.87; for girls, the best equation was Dl_COsb = exp(1.56516 + [0.0193 × age] + [0.00893 × height] + [0.00273 × weight]), R² = 0.75. The single-breath transfer coefficient of the lung for carbon monoxide remained constant with age and height, with a lower limit of normal of 6.5 ml/min/mm Hg/L in boys and 5.4 ml/min/mm Hg/L in girls. Measured Dl_COsb was higher than predicted by other authors (P < 0.001 by paired t test).

Individuals 4-20 years of age can complete high-quality Dl_COsb tests. Children and adolescents living at 2,240 m have higher Dl_COsb values than those living at sea level. Reference equations for Dl_COsb obtained at sea level are poor predictors of the values measured at moderate altitude.