Power spectral analysis of heart rate variability (HRV) provides a powerful non-invasive too] for exploring the balance between sympathetic and parasympathetic components of the autonomic nervous system. In the spectrum of HRV, there are three distinct peaks. The high frequency (HF) band (0.15 to 0.4 Hz) is correlated with parasympathetic activity and this is the band of interest 'in the study.

Two OTOUPS Of SL113jeCtS were considered in this work, stroke survivors and subjects performing an oral presentation in front of an audience. Data were collected with a Holter monitor to allow for ambulatory recording. Respiration was derived from the EKG and was used to determine the parasympathetic frequency band in the HRV spectrum.

The power spectral analysis of HRV from stroke survivors revealed significantly less parasympathetic activity than in control subjects. Sustained low variation of heart rate suggested that stroke' survivors may suffer from one or more aspects of autonomic nervous system imbalance.

The power spectral analysis of HRV from normal subjects during a formal presentation revealed that vagal activity decreased significantly with the anticipation of making a presentation as well as during the presentation in the presence of an audience, when compared to vagal activity during a presentation without an audience.