External dead space explains sex-differences in the ventilatory response to submaximal exercise in children with and without obesity

We compared the exercise ventilatory response (slope of the ventilation, (V) over dot(E) and carbon dioxide production, (V) over dotCO(2) relationship) in boys and girls with and without obesity. 46 children with obesity (BMI percentile: 97.7 +/- 1.4) and 27 children without obesity (BMI percentile: 55.1 +/- 22.2) were included and divided into groups by sex (with obesity: 17 girls and 29 boys; without obesity: 13 girls and 14 boys). A 6 min constant load cycling test at 45 % of peak work rate was performed. The (V) over dot(E)/(V) over dotCO(2) slope was similar (p = 0.67) between children with (32.7 +/- 4.3) and without (32.2 +/- 6.1) obesity; however, it was higher (p = 0.02) in girls (35.4 +/- 5.6) than boys (32.6 +/- 4.9). We also examined a corrected (V) over dot(E) /(V) over dotCO(2) slope for the effects of mechanical dead space Num), by subtracting VDM from (V) over dot(Ecorr)/VCO2 slope). The (V) over dot(Ecorr)/(V) over dotCO(2) slope remained similar (p = 0.37) between children with (26.8 +/- 3.2) and without obesity (26.1 +/- 3.1); however, no sex differences were observed (p = 0.13). Therefore, VDM should be accounted for before evaluating the (V) over dot(E)/(V) over dotCO(2) slope, particularly when making between-sex comparisons.