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.