Tachycardia in adults with cystic fibrosis is associated with normal autonomic function

Background: Whether autonomic dysfunction contributes to tachycardia in cystic fibrosis (CF) is unknown. Methods: Heart rate variability (HRV) was assessed to determine high frequency power and the low/high frequency power ratio (HF, LF/HF) as markers of vagal and sympathovagal balance, respectively, under spontaneous and controlled breathing (15 breaths per minute (bpm)) conditions in 17 CF and 17 healthy control subjects. Results: Under spontaneously breathing conditions, the CF group was tachycardic (75.4 ±11.2 vs 60.2 ±9.0 br/min P < 0.001) and tachypnoeic (22.6 ±5.8 vs 13.6 ±4.1 br/min, P= 0.001) compared with controls. No significant difference in HRV was observed between groups during spontaneous or controlled breathing. Coexistent diabetes mellitus and β₂ agonist use were not associated with altered autonomic control. During controlled breathing, the CF group showed a negative correlation between forced expiratory volume in 1 s (FEV₁) % predicted and HF power (P= 0.013, r=?0.59) and a positive correlation between FEV₁ % predicted and LF/HF ratio (P= 0.002, r= 0.69) suggesting an exaggerated normal vagal response. Conclusion: CF patients have normal autonomic function.