Temporal increment distributions of RR-intervals reveal dynamics of cardiac regulation in head-up tilt test

Dynamical aspects of cardiovascular regulation are revealed in the head-up tilt test by the properties of the distribution of time-increments between subsequent heart contractions. The Generalized Porta Index (GPI) is introduced and then calculated for the pooled probability density functions. GPI reveals marked differences between the dynamical response to the tilt test of healthy subjects prone to spontaneous fainting and those who are less susceptible.