Power spectra of blood pressure and heart rate fluctuations during mental load

The aim of the present paper was a search of a respiration‐independent factor changing the power spectra of circulatory parameters during mental load. Blood pressure, heart rate and respiratory movements were recorded in 12 subjects (age 19–23) in 4 experimental periods, 5 minutes each: at rest ‐ period 1 ‐ and during a mental load (discrimination between 3 tones of different pitch) ‐ period 2. Then the record of respiration from periods 1 and 2 was replayed on the oscilloscopic screen and the subject had to reproduce his own previous respiratory movements ‐ period 3 and 4. The power spectra of all parameters recorded in periods 1 and 3, and 2 and 4 were compared; the reproduction of the respiration as a week mental load was taken into consideration. There is some tendency of mental load to damp the power spectral density of circulatory parameters in all frequency ranges (minutes waves, 10‐second rhythm and respiratory oscillations), but in some subjects expressive opposite changes occurred. We did not find any respiration‐ independent change in circulatory spectra stable enough to make possible the use of spectral analysis to measure the mental load intensity.