In this chapter the effects of mental effort during task performance are studied on heart rate, blood pressure and its spectral variability measures as well as effects on baroreflex sensitivity also using a spectral method. In particular, differential effects of task complexity is looked at. On heart rate about the same effects are found as in other laboratory studies on mental workload: an increase of heart rate and a decrease in variability. The pattern in blood pressure is about the same: an increase in pressure during mental effort and a decrease of blood pressure variability. In most cases also baroreflex sensitivity is decreased.

The second part of the paper is directed to differential effects between tasks. It is found that the mid and higher frequency part of the heart rate spectrum shows the largest effects of task complexity. Changes in respiratory pattern during task performance are studied to get a better insight in the possible reasons for these differences. It is concluded that differences in breathing pattern can possibly partly explain rest-task changes in variability measures. However, differences in spectral measures between tasks can not be attributed to respiratory patterns. These latter effects have to be ascribed to an additional vagal inhibition during complex task performance.