  This paper proposes a prototype of a new biofeedback training based on
mathematical models of cardiovascular control. For this purpose we develop a
low-cost device that is able to record and process arterial pulse wave via
photoplethysmograph and skin temperature on the peripheral part of the arm. A
benchmark analysis of our device against a registered cardiovascular
measurement system (Biopac MP35 from Biopac Inc., USA) shows that heart rate
and skin temperature values delivered by our device are acceptable with a very
low residual error (+/-1 beat/min, +/-1 oC).
  Both measured signals are feed into a mathematical model which estimates the
level of activity of both sympathetic and parasympathetic branches of the
autonomic nervous system. That information is used jointly with other
biological parameters for investigating the stress score of the subject. The
data is processed in real-time and continuously displayed to the user for
effective biofeedback training.
  The complete solution was preliminary tested on three volunteers who used the
displayed biofeedback information in order to regulate their emotional state
successfully during Biofeedback training. They exhibited a significant
reduction in stress score compared to three control subjects who did not used
our solution during biofeedback training. This supports the benefits of
biofeedback training with autonomic nervous tone assessment as effective
holistic healing method.
