Cardiac vagal tone in generalised anxiety disorder.

The aim of the present study was twofold: firstly, to determine cardiac vagal tone in subjects with generalised anxiety disorder directly, using an invasive pharmacological method; and secondly, to test whether the non-invasive method of measuring the amplitude of respiratory sinus arrhythmia (RSA) gives a reliable estimate of cardiac vagal tone in this form of anxiety disorder. Comparison of baseline physiological measures of anxious and control subjects revealed that cardiac vagal tone and heart rate were not different in the two groups of subjects, whereas length of the respiratory cycle and amplitude of respiratory sinus arrhythmia were reduced in the former group. Because of the higher respiratory rates of anxious subjects, the RSA method was found to underestimate cardiac vagal tone in generalised anxiety disorder.