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Timing and Driving Components of the Breathing Strategy in Children With Cystic Fibrosis During Exercise.
Keochkerian, D. PhD 1; Chlif, M. PhD 1; Delanaud, S. PhD 2; Gauthier, R. MD 3; Maingourd, Y. MD, PhD 1,4; Ahmaidi, S. PhD 1*
[Article] Pediatric Pulmonology. 40(5):449-456, November 2005.

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: The aim of this study was twofold: first, to determine the breathing strategies of children with cystic fibrosis (CF) during exercise, and secondly, to see if there was a correlation with lung function parameters. We determined the tension-time index of the inspiratory muscles (TT0.1) during exercise in nine children with CF, who were compared with nine healthy children with a similar age distribution. TT0.1 was determined as followed TT0.1 = P0.1/PImax [middle dot] TI/TTOT, where P0.1 is mouth occlusion pressure, PImax is maximal inspiratory pressure, and TI/TTOT is the duty cycle. CF children showed a significant decrease of their forced expiratory volume in 1 sec (FEV1), forced vital capacity (FCV), and FEV1/FVC, whereas the residual volume to total lung capacity ratio (RV/TLC) ratio and functional residual capacity (FRC) were significantly increased (P<0.001). Children with CF showed mild malnutrition assessed by actual weight expressed by percentage of ideal weight for height, age, and gender (weight/height ratio; 82.3 /-3.6%). Children with CF showed a significant reduction in their PImax (69.3 /- 4.2 vs. 93.8 /- 7 cmH2O). We found a negative linear correlation between PImax and weight/height only in children with CF (r=0.9, P<0.001). During exercise, P0.1, P0.1/PImax, and TT0.1 were significantly higher, for a same percent maximal oxygen uptake in children with CF. On the contrary, TI/TTOT ratio was significantly lower in children with CF compared with healthy children. At maximal exercise, children with CF showed a TT0.1 = 0.16 vs. 0.14 in healthy children (P< 0.001). We observed at maximal exercise that P0.1/PImax increased as FEV1/FVC decreased (r=-0.90, P<0.001), and increased as RV/TLC increased (r = 0.92, P< 0.001) only in children with CF. Inversely, TI/TTOT decreased as FEV1/FVC decreased (r=0.89, P<0.001), and TI/TTOT decreased as RV/TLC increased (r=-0.94, P<0.001). These results suggest that children with CF adopted a breathing strategy during exercise in limiting the increase of the duty cycle. Two determinants of this strategy were degrees of airway obstruction and hyperinflation.