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.

Determinants of dyspnea and alveolar hypoventilation during exercise in cystic fibrosis: Impact of inspiratory muscle endurance

“…Previous studies have reported a 15 to 40% reduction in maximum static inspiratory mouth pressure in CF patients with moderate airflow obstruction [27,[31][32][33]. The present study demonstrated a 22% reduction of PImax in adults CF patients with moderate to severe obstructive ventilatory defect.…”

Inspiratory Muscle Strength and Endurance in Children and Adolescents with Cystic Fibrosis

“…3,4,28,29 Dunnink et al 4 suggest that the increased work of breathing due to airway obstruction could cause an effect of conditioning the respiratory muscles. On the contrary, some studies 5,12,30,31 showed a reduction of respiratory muscle strength, associating this finding with hyperinflation and malnutrition. Furthermore, Dassios et al 32 showed that maximum respiratory pressures were significantly diminished in subjects with no severe lung disease; however, no correlation between P Imax and BMI was found.…”

Inspiratory muscle strength relative to disease severity in adults with stable cystic fibrosis

“…The inspiratory muscles must possess sufficient capacity relative to the imposed inspiratory load for normal breathing to occur in the presence of this excess WOB [5]. CF-related inspiratory muscle impairments may contribute to respiratory pump dysfunction, dyspnea, altered breathing patterns, inspiratory fatigue, and ultimately exercise intolerance [4][5][6][7][8].…”