Does the sympathetic nervous system influence sinus arrhythmia in man? Evidence from combined autonomic blockade.

Abstract

The influences of vagal and sympathetic efferent activity on sinus arrhythmia in man were studied in healthy subjects by administration of hyoscine butylbromide and atenolol alone and combined using a microcomputer-linked ECG system. Sinus arrhythmia was quantitated as the SD of the R-R interval. Sinus arrhythmia was reduced by hyoscine butylbromide, in some subjects to near abolition, but this end-point was unchanged by pre-treatment with atenolol. Atenolol alone prolonged the mean R-R interval and increased sinus arrhythmia. Apparently sinus arrhythmia in man is mediated through vagal efferents alone but atenolol increases the arrhythmia through a central vagotonic effect.