Relationship between Passive and Active Pulsations of Rat Artery as Vascular Extension of Frank-Starling Law

The experiments on narcotized male rats (n=30) determined the parameters of passive and active pulsatile modes of isolated segment of femoral artery in situ. Rheographic elasticity (RE) and reactivity (RR) were correspondingly determined as the ratios of peak-to-peak (p2p) magnitudes of passive and active pulsatile oscillations of arterial electroimpedance (AEI) to p2p magnitude of BP undulations. The medians and interquartile ranges of RE and RR were 6 (3; 11) and 70 (40; 110) mΩ/mm Hg, respectively. The maximal and minimal values of RE and RR in various rats differed by 50 and 80 times, respectively, and were bimodally distributed: in major group (n=23), the values were RE<15 and RR<200 mΩ/mm Hg, whereas in minor group (n=7), these parameters were RE>20 and RR>300 mΩ/mm Hg. The above ranges of RE and RR parameters were considered as the diagnostic signs of normal and pseudo-healthy rats with pathologically augmented AEI oscillations, respectively. Statistical analysis of all rats (n=30) revealed the positive correlation between RE and RR (r=0.76) with linear regression RR=31+7.6×RE. It is hypothesized that this correlation is underlain by a mechanism similar to that described by the Frank-Starling law for myocardium.