All signals were amplified by a custom designed battery powered bridge amplifier with an adjustable gain. All amplified signals, including amplified ECG, will then be fed to a high-performance data acquisition A/D converter for notebook PC. Data will be stored on a personal computer hard drive for off-line reanalysis. Graphical presentations of results will be performed using the AxoScope 10.2, software developed by Axon Instruments, Inc., 3280 Whipple Road, Union City, CA 94587 USA.