AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 4 710-R719, Copyright © 1987 by American Physiological Society
Normalization of hemodynamic parameters: application to vascular resistance and impedance
Z. R. Liu and F. C. Yin
Comparison of hemodynamic parameters among different species is complicated
by the wide variety of body sizes and shapes. Although some parameters such
as blood pressure and flow velocity seem to have similar absolute values
among species, most other parameters such as cardiac output, pulse wave
velocity, and heart rate vary greatly. Comparisons would be facilitated if
one uses indices that are independent of body size and/or shape. An ideal
index will bring values for individuals or species of different sizes into
the same range and yet exhibit large relative changes to responses to small
increments of an intervention in an individual. In this paper we
demonstrate how dimensional analysis together with Buckingham's pi theorem
and the assumption of biological similarity can be used to derive
dimensionless hemodynamic normalization indices. Using data from the
literature and from our own laboratory, we illustrate the approach by
examining resistance and impedance. We compare our results with previously
proposed methods of accounting for different body sizes, namely, dividing
impedance by resistance or vice versa, multiplying by body weight, and
using flow velocity rather than volume flow in the calculations. Both of
our proposed indices bring the values for arterial and pulmonary resistance
and impedance for rats, rabbits, dogs, and humans into the same range,
although the variability among species using our indices is twice that of
those previously proposed. On the other hand, the relative changes of our
two indices induced by vasoactive agents or exercise in a dog are from two
to five times greater than either the absolute values themselves or the
previously used indices.
