Information about the activity of the autonomie nervous system can be derived by analysis of key physiological signals, including ECG and blood pressure, on a beat-to-beat basis. Due to the large amount of data and mathematical processing involved, analysis by hand is prohibitive. The solution developed facilitates this procedure by performing the processing on a PC-based instrument incorporating existing medical equipment, a data acquisition board and a computer program to acquire and process the physiological signals. The automated virtual instrument was written using LabVIEW as the main platform. The techniques implemented include impedance cardiography, time- and frequency-domain analysis, invasive and non-invasive baroreflex sensitivity assessment, and forearm blood flow measurements. The system was designed to study patients suffering vasovagal blackouts, where the changes that occur in the heart and circulation during an attack could increase understanding of the physiological processes that underlie their blackouts.