Differential Laws of Left
Ventricular Isovolumic Pressure Fall
S. F. J. LANGER
Institute of Physiology, Free University Berlin, Germany
Received July 20, 2000
Accepted June 7, 2001
Summary
An attempt has been made to test for a reliable method of characterizing the
isovolumic left ventricular pressure fall in isolated ejecting hearts by one or
two time constants, tau. Alternative nonlinear regression models (three and
fourparametric exponential, logistic, and power function), based upon the
common differential law dp(t)/dt =  [p(t)Ptau]/ tau(t) are compared in
isolated ejecting rat, guinea pig, and ferret hearts. Intraventricular pressure
fall data are taken from an isovolumic standard interval and from a subinterval
of the latter, determined datadependently by a statistical procedure. Extending
the threeparametric exponential fitting function to fourparametric models
reduces regression errors by about 2030 %. No remarkable advantage of a
particular fourparametric model over the other was revealed. Enhanced
relaxation, induced by isoprenaline, is more sensitively indicated by the
asymptotic logistic time constant than by the usual exponential. If early and
late parts of the isovolumic pressure fall are discarded by selecting a
subinterval of the isovolumic phase, ? remains fairly constant in that central
pressure fall region. Physiological considerations point to the logistic model
as an advantageous method to cover lusitropic changes by an early and a late
tau. Alternatively, identifying a central isovolumic relaxation interval
facilitates the calculation of a single ("central") tau; there is no statistical
justification in this case to extend the threeparametric exponential further to
reduce regression errors.
Key words
Ventricular relaxation · Relaxation time constant · Rat · Guinea
pig · Ferret
Reprint requests
Dr. Stefan F. J. Langer, Institute of Physiology, Free University
Berlin, Arnimallee 22, D14195 Berlin, Fed. Rep. of Germany.
Phone: (+4930) 84451649, Fax: (+4930) 84451602, email:
sflanger@zedat.fuberlin.de
