Isovolumic relaxation period (IRP) and the time constant of left ventricular pressure decay (T) were significantly altered in the same direction by changes in afterload in an experimental dog model.
Does the isovolumic relaxation period (IRP) accurately reflect left ventricular relaxation under different afterload conditions compared to the time constant of left ventricular pressure decay (T)?
The isovolumic relaxation period reliably reflects left ventricular relaxation across different afterload conditions, serving as a simple alternative to the time constant of left ventricular pressure decay.
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.
Ochi et al. (Sun,) conducted a other in Left ventricular relaxation (n=17). Afterload alteration (angiotensin II, nitroprusside, aortic constriction) was evaluated on Correlation between isovolumic relaxation period (IRP) and left ventricular pressure decay time constant (T). Isovolumic relaxation period (IRP) and the time constant of left ventricular pressure decay (T) were significantly altered in the same direction by changes in afterload in an experimental dog model.