Effects of Spontaneous and Forced Swallowing on Cardiac Autonomic Regulation
Introduction: The relationship between the digestive tract and the cardiovascular system has been described in the literature and both present vagal activity in common. Tachycardia peaks were observed before swallowing in electrocardiogram. The heart rate variability (HRV) is a method well recognized in the literature and analyzes the autonomic cardiac regulation. However, it is unclear whether there is an effect of spontaneous and forced swallowing on HRV.
Method: The study was conducted in 10 young adult male and 7 female subjects between 18 and 35 years old. Linear indices of HRV are analyzed. The protocols were separated into two steps: (1) forced swallowing for 5 minutes (1 per minute); (2) spontaneous swallowing for 5 minutes.
Results: We observe that the root mean square of the successive differences (RMSSD [p = 0.02]), pNN50 (p = 0.007), low frequency (LF [nu] [p = 0.0024]), high frequency (HF [ms2] [(p = 0.0008]), and HF (nu) indices (p = 0.0025) increased during the spontaneous swallowing compared with forced swallowing in men. The RMSSD index tended to increase in spontaneous swallowing compared to forced swallowing in women (p = 0.064). However, no significant difference was found for pNN50 (p = 0.139), LF (nu) (p = 0.258), HF (ms2) (p = 0.363), and HF (nu) (p = 0.402) indices between spontaneous and forced swallowing in women.
Conclusion: Forced swallowing reduces parasympathetic component of heart-rate modulation and decreases HRV.