Does the sympathetic nervous system influence sinus arrhythmia in healthy subjects?
Sinus arrhythmia in humans appears to be mediated through vagal efferents alone, with atenolol increasing the arrhythmia likely through a central vagotonic effect.
The influences of vagal and sympathetic efferent activity on sinus arrhythmia in man have been studied in healthy subjects by administration of hyoscine butylbromide and atenolol alone and combined using a microcomputer-linked electrocardiogram (e.c.g.) system. Sinus arrhythmia was quantitated as the S.D. 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. It is suggested that sinus arrhythmia in man is mediated through vagal efferents alone but that atenolol increases the arrhythmia through a central vagotonic effect.
Coker et al. (Thu,) studied this question.