| Background: Cystic fibrosis (CF) is a multisystem disease that affects the cardiorespiratory system and the cardiac autonomic control may be altered at rest and after a submaximal exercise. Objective: To assess the cardiac autonomic control by heart rate variability (HRV) analysis before and after a 6-minute walk test (6MWT). Method: Thirteen children diagnosed with Cystic Fibrosis (CFG) aged 12±2.7 years (FEV 1 /FVC: 0.83±0.11, FEV 1 : 71.4±21 %pred) and 12 healthy children (control group-CG) aged 11.4±2.4 years (FEV 1 /FVC: 0.91±0.12, FEV 1 : 91.6±17.4 %pred) were included in the study. HRV was evaluated prior to and immediately after the 6MWT and the heart rate recovery assessed on the first and second minute after test.

Positive Expiratory Pressure (PEP) improves lung function, however, PEP-induced changes are not fully established. The aim of this study was to assess the acute effects of different PEP levels on chest wall volumes and the breathing pattern in children with Cystic Fibrosis (CF). Anthropometric data, lung function values, and respiratory muscle strength were collected. Chest wall volumes were assessed by Optoelectronic plethysmography at rest and during the use of different PEP levels (10 and 20 cm H2O), randomly chosen. Eight subjects with CF (5M, 11.5±3.2 years, 32±9.5 kilograms) and seven control subjects (4M, 10.7±1.5 years, 38.2±7.8 kilograms) were recruited. The CF group showed significantly lower FEF values 25-75% (CF: 1.8±0.8 vs. CG: 2.3±0.6) and FEV1/FVC ratio (CF: 0.8±0.1 vs. CG: 1±0.1) compared with the control group (p<0.05). Different PEP levels increased the usual volume in chest wall and its compartments in both groups; however, this volume was significantly higher in the control group compared with the CF group during PEP20 (CW: 0.77±0.25 L vs. 0.44±0.16 L; RCp: 0.3±0.13 L vs. 0.18±0.1 L; RCa: 0.21±0.1 L vs. 0.12±0.1 L; AB: 0.25±0.1 L vs. 0.15±0.1 L; p<0.05 for all variables). Minute ventilation was significantly higher during PEP compared with breathing at rest in both groups (p<0.005). End-expiratory volume was also higher during PEP compared with breathing at rest for chest wall and pulmonary rib cage in both groups (p<0.05). Different PEP levels may increase chest wall volumes in CF patients.

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