Changes in Swallowing-Related Tachycardia and Respiratory Arrhythmia Induced by Modulation of Tonic Parasympathetic Influences

In 19 tested persons in the resting lying position, we examined changes in the mean duration of R-R intervals ((R-R) over bar) and in parasympathetic chronotropic cardiac reactions (respiratory arrhythmia, RA, and swallowing-related tachycardia, ST) induced by intensified tonic parasympathetic influences after peroral administration of antagonists of muscarinic (M) receptors in small doses. Administration of 0.02 g of an extract of Belladonna, which contains alkaloids of the atropine group, led to a significant (R-R) over bar increase (P < 0.001). In this case, the RA at the natural frequency of breathing (P < 0.05) and ST (P < 0.001) simultaneously increased. Close correlation was observed both between initial values of the ST and <(R-R)over bar> in various tested persons (r = 0.87) and between changes in these values, which were induced by the action of small amounts of. antagonists (r = 0.84). In various persons, the RA during deep slowed breathing (6 min(-1), RA 6) demonstrated ambiguous modifications. In the structure of RA 6, we identified two components: an inspiratory tachycardic (TC) and an expiratory bradycardic (BC). With intensification of the parasympathetic influences, the TC began to prevail; its increase was strongly related to a rise in the (R-R) over bar (r = 0.84). In contrast, correlation between changes in the BC and an increase in the (R-R) over bar was completely absent (r = 0.001). Therefore, small amounts of. antagonists intensify both the tonic component of parasympathetic control (increasing the (R-R) over bar) and its dynamic indices, the magnitudes of the ST and RA. Tachycardia during swallowing and the inspiratory TC under conditions of deep slowed breathing are closely related to changes in the parasympathetic influences. The magnitude of the RA is the index, which reflects the tonic component of chronotropic control under conditions of both slowed and natural breathing less adequately than the ST.