title: Isovolumic relaxation period as an index of left ventricular relaxation under different afterload conditions--comparison with the time constant of left ventricular pressure decay in the dog.
abstract: In order to determine whether isovolumic relaxation period (IRP) reflects left ventricular relaxation under different afterload conditions, 17 anesthetized, open chest dogs were studied, and the left ventricular pressure decay time constant (T) was calculated. In 12 dogs, angiotensin II and nitroprusside were administered, with the heart rate constant at 90 beats/min. Multiple linear regression analysis showed that the aortic dicrotic notch pressure (AoDNP) and T were major determinants of IRP, while left ventricular end-diastolic pressure was a minor determinant. Multiple linear regression analysis, correlating T with IRP and AoDNP, did not further improve the correlation coefficient compared with that between T and IRP. We concluded that correction of the IRP by AoDNP is not necessary to predict T from additional multiple linear regression. The effects of ascending aortic constriction or angiotensin II on IRP were examined in five dogs, after pretreatment with propranolol. Aortic constriction caused a significant decrease in IRP and T, while angiotensin II produced a significant increase in IRP and T. IRP was affected by the change of afterload. However, the IRP and T values were always altered in the same direction. These results demonstrate that IRP is substituted for T and it reflects left ventricular relaxation even in different afterload conditions. We conclude that IRP is a simple parameter easily used to evaluate left ventricular relaxation in clinical situations.
authors.affiliation: Fourth Department of Internal Medicine, Shimane Medical University, Izumo, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Ochi
authors.forename: I
authors.initials: I
authors.lastname: Ikuma
authors.forename: H
authors.initials: H
authors.lastname: Toda
authors.forename: T
authors.initials: T
authors.lastname: Shimada
authors.forename: S
authors.initials: S
authors.lastname: Morioka
authors.forename: K
authors.initials: K
authors.lastname: Moriyama
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D004285:Dogs; D004452:Echocardiography; D004562:Electrocardiography; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006352:Heart Ventricles / Q000187:drug effects; D007537:Isometric Contraction / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D009599:Nitroprusside / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D012044:Regression Analysis; D013997:Time Factors; D014661:Vasoconstriction / Q000187:drug effects; D016276:Ventricular Function
chemical_list: D000804:Angiotensin II; D009599:Nitroprusside; D011433:Propranolol