Effects of autonomic blockade on self-similarity of blood pressure and heart rate time series

Little is known on the effects of autonomic alterations on the characteristics of self-similarity of cardiovascular time series. To clarify this issue, changes in scaling exponents for blood pressure and heart rate following sympathetic and parasympathetic blockades were studied. We recorded RR interval (RRI) and mean arterial pressure (MAP) beat by beat in 8 volunteers before and after administration of: propranolol, a non specific beta1 and beta2 cardiac and vascular antagonist; clonidine, an alpha2 agonist; and atropine, blocker of cardiac vagal activity. Self-similarity coefficients for RRI, H
_RRI
, and MAP, H
_MAP
, were estimated by detrended fluctuations analysis. Under baseline condition, H
_MAP
was significantly greater than H
_RR
. Sympathetic blockades reduced H
_RRI
only, while vagal blockade increased both H
_RRI
and H
_MAP
. Results revealed differences in the scaling structures of MAP and RRI, and in the way their self-similarity is influenced by the autonomic regulation