Do the deceleration/acceleration capacities of heart rate reflect cardiac sympathetic or vagal activity? A model study.

Despite increased application of the deceleration capacity (DC) and acceleration capacity (AC) of heart rate indices as indicators of autonomic nervous system (ANS) function, it remains controversial as to whether they reflect cardiac sympathetic or vagal activity. We addressed this problem using a cardiovascular system model that allows analysis of DC and AC under controllable levels of sympathetic and vagal activities. Multi-scale DCs and ACs with various timescales T and wavelet scales s were computed from the simulated RR interval series under randomly fluctuating levels of ANS activity, and the correlations of the indices to ANS functions were assessed. Results showed that under the conventional scales (T = 1, s = 2), both DC and AC were solely dependent on vagal activity. With higher scales (T = 3, s = 5), both DC and AC were positively correlated to sympathetic activity and negatively correlated to vagal activity. These data suggest that DC and AC provide information on the same aspects of ANS activity and that their physiological significance is highly influenced by the timescales and wavelet scales used in the computation.