Abstract
The interbeat interval, peripheral blood flow and respiration waveform of 14 subjects were measured during three mental tests of different intensity and during 10 min recovery time after each test. The signals were analysed using a general statistical package and a spectrum analysis procedure. It was shown that the respiration frequency component moved to a higher frequency during mental tests and returned to its original frequency during the recovery periods. The mean heart rate increased by 15% during the tasks and the heart rate variability decreased.