Dynamics of swallowing-induced cardiac chronotropic responses in healthy subjects

Simultaneous recording of ECG and swallowing movements in healthy humans (n=23, age 20-57 years) showed that each swallow is accompanied by transient tachycardia with initial abrupt and pronounced heart rate increase. These rapid changes in heart rate (evaluation by maximum increment of heart rate over two successive heartbeats, Delta HR(2bt)) are typical of vagal chronotropic responses. The amplitude of tachycardia induced by a single swallow was significantly higher in the supine position (13.1 +/- 5.6 bpm) compared to the standing position (8.5 +/- 3.8 bpm; p<0.0001). Chronotropic responses to a series of three or more successive swallows consisted of two phases, the initial abrupt acceleration and subsequent slower growth of heart rate. In the standing position, the portion of the first rapid phase significantly decreased, while the portion of the slower phase increased compared to the supine position. The amplitude of tachycardia induced by a single swallow and parameter Delta HR(2bt) can serve as indices of the strength of parasympathetic modulation of the heart. By contrast, further slow increase in the heart rate determined by summation of responses to a series of successive swallows can result from not only inhibition of the parasympathetic influences, but also enhancement of sympathetic activity during swallowing.