Regional Differences in Relaxation Time (τ): Its Relationship to Intraventricular Pressure Gradients in a Canine and Hydraulic Model

The role of elastic recoil in producing intraventricular pressure gradients (IVPG) is well known. The influence of other physiologic variables however remains unclear. The aim of this study was therefore to investigate in a combined canine and hydraulic model experiment the role of regional differences in left ventricle (LV) relaxation in producing IVPG. In the canine model, the LV relaxation time constant (τ) was significantly shorter at the apex comparedto the base of the LV at baseline, during isoproterenol infusion and during esmolol infusion. IVPG rose significantly with isoproterenol and fell with esmolol compared to baseline values. Multivariate analysis demonstrated both Δτ and τ to contribute significantly to predicting IVPG. These findings were supported by similar measurements in a hydraulic model, which showed IVPG to be closely related to Δτ. In addition, the in vitro results suggested that higher LV compliance is associated with increased IVPG. This study demonstrated that in addition to elastic recoil, regional relaxation differences significantly impact IVPG. Assessment of IVPG, now available noninvasively, could provide useful clinical insight into cardiac ischemia and diastolic dysfunction.