title: Timing and driving components of the breathing strategy in children with cystic fibrosis during exercise.
abstract: 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 (T(T0.1)) during exercise in nine children with CF, who were compared with nine healthy children with a similar age distribution. T(T0.1) was determined as followed T(T0.1) = P0.1/PImax . T(I)/T(TOT), where P0.1 is mouth occlusion pressure, PImax is maximal inspiratory pressure, and T(I)/T(TOT) 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, P(0.1), P0.1/PImax, and T(T0.1) were significantly higher, for a same percent maximal oxygen uptake in children with CF. On the contrary, T(I)/T(TOT) ratio was significantly lower in children with CF compared with healthy children. At maximal exercise, children with CF showed a T(T0.1) = 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, T(I)/T(TOT) decreased as FEV1/FVC decreased (r = 0.89, P < 0.001), and T(I)/T(TOT) 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.
authors.affiliation: EA 3300-APS et Conduites Motrices: Adaptations et Réadaptations, Université Picardie Jules Verne, Amiens, France.
authors.forename: D
authors.initials: D
authors.lastname: Keochkerian
authors.forename: M
authors.initials: M
authors.lastname: Chlif
authors.forename: S
authors.initials: S
authors.lastname: Delanaud
authors.forename: R
authors.initials: R
authors.lastname: Gauthier
authors.forename: Y
authors.initials: Y
authors.lastname: Maingourd
authors.forename: S
authors.initials: S
authors.lastname: Ahmaidi
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D001827:Body Height / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D016022:Case-Control Studies; D002648:Child; D003550:Cystic Fibrosis / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D044342:Malnutrition / Q000503:physiopathology; D010101:Oxygen Consumption / Q000502:physiology; D012119:Respiration; D012129:Respiratory Function Tests; D012132:Respiratory Muscles / Q000503:physiopathology*