title: Measurement of ventricular relaxation. An alternative index of isovolumic relaxation to the time constant.
abstract: The time constant (T) is commonly used for representing the isovolumic fall in left ventricular pressure (LVP) because the isovolumic fall is monoexponential under most circumstances. However, the determination of T is cumbersome due to the requirement of a set of LVP versus time values in fitting a monoexponential function. RT64, which is the time from the minimum value of the time derivative of LVP (-dp/dtmax) to 36% of -dP/dtmax, can be derived beat-by-beat, on-line, and may be a simple alternative to T. Through the use of 240 pairs of values derived from six conscious instrumented dogs treated with different cardiovascular active agents, RT64 and T were found to be significantly correlated (r = 0.835, p less than 0.05) according to the equation RT64 = 0.725T + 10.2. In conclusion, RT64 may provide a simple alternative to T in representing the isovolumic relaxation process of the left ventricle.
authors.affiliation: Cardiovascular Pharmacology, Wyeth Laboratories, Inc., Philadelphia, Pennsylvania.
authors.forename: K C
authors.initials: KC
authors.lastname: Lee
mesh_terms: D000818:Animals; D001341:Autonomic Nervous System / Q000502:physiology; D004285:Dogs; D004562:Electrocardiography; D006321:Heart / Q000502:physiology*; D006439:Hemodynamics / Q000187:drug effects; D006584:Hexamethonium Compounds / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008954:Models, Biological; D009200:Myocardial Contraction / Q000187:drug effects; D010656:Phenylephrine / Q000494:pharmacology; D012119:Respiration; D014700:Verapamil / Q000494:pharmacology
chemical_list: D006584:Hexamethonium Compounds; D010656:Phenylephrine; D014700:Verapamil; D007545:Isoproterenol