A case of respiratory sinus arrhythmia and vasovagal attacks: use of cosinor analysis for diagnosis and for monitoring treatment.

An 18 year old girl presented with frequent vasovagal attacks and sinus arrhythmia. The amplitude of respiratory sinus arrhythmia assessed by cosinor analysis was 20%; the predicted value for a normal girl of this age is 4% and the 95% confidence interval is 0-8%. Treatment with propantheline, in a dose sufficient to reduce the amplitude of sinus arrhythmia to normal, abolished her symptoms.