Heart rate variability at rest and after the 6-minute walk test (6MWT) in children with cystic fibrosis.

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 (FEV1/FVC: 0.83±0.11, FEV1: 71.4±21 %pred) and 12 healthy children (control group-CG) aged 11.4±2.4 years (FEV1/FVC: 0.91±0.12, FEV1: 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. RESULTS Prior to exercise, CF patients presented higher values for the variables LF(nu) (53.2±15.0 vs. 32.8±7.9, p=0.0003) and LF/HF (1.25±0.72 vs. 0.49±0.18, p<0.006) as well as lower values of HF(%) (25.4±18.4 vs. 53±9.6, p=0.002) and HF(nu) (47.3±14.7 vs. 68.3±8.7, p0.001) when compared to CG. After the 6MWT, both groups demonstrated HRV recovery to baseline levels; however, the differences between CFG and CG were maintained for the variables LF(ms 2) (846.7±754.8 vs. 345.6±197.2, p=0.02); LF(%) (35.4±8.1 vs. 25.9±6.2, p=0.002); LF(nu) (60.0±16.3 vs. 34.9±8.7, p<0.0001); HF(%) (27.4±13.7 vs. 48.1±6.3, p=0.0003); HF(nu) (40.4±15.8 vs. 65.6±8.2, p=0.0003) and LF/HF (1.9±1.7 vs. 0.5±0.2, p=0.0001). CONCLUSIONS Children with cystic fibrosis exhibited predominance of sympathetic activity at rest that persisted after the 6-minute walking test when compared to the control group.