Alberico Sabbadini joined our group as PhD student
Alberico started his PhD on 1 December. He will work on a method for early diagnosis of stiffening of the heart, which employs non-invasive ultrasound imaging and allows early identification of (patients at risk of developing) heart failure. The new method is based on the natural shear waves in the heart muscle, which find their origin in the natural “noise-like” mechanical excitations caused by the beating heart, flowing blood, breathing, etc. The propagation velocity of the resulting natural shear waves is dependent on the local stiffness of the heart muscle.
The tissue stiffness depends in a nonlinear way on the instantaneous strain, so that many co-founding factors such as preload, afterload, heart rate, chamber volume, and wall thickness play an intricate role in extracting the local tissue stiffness from the local shear wave velocity. Numerical models of increasing complexity, and in-vitro, ex-vivo and animal in-vivo experiments will be applied to explore the relation between the observed local shear wave velocities and the co-factors on the one hand, and the tissue shear stiffness on the other hand.
A next step consists of transforming this data into a relation between the pressure and the heart volume. Here, one of the challenges is to deal with the fact that the shear stiffness (and in fact the shear wave velocities) are dependent on the co-factors and thus on time. Another challenge to be addressed is the relation between the shear stiffness and the Young’s modulus of heart tissue, where the latter determines the chamber compliance. These challenges will be addressed by numerical modelling and by animal in-vivo tests.
From the obtained pressure-volume relationship, a clinically applicable parameter can be derived. It is well known that the relation between the Young’s modulus of cardiac tissue and the strain determines the chamber compliance in diastole (the so-called end-diastolic pressure-volume relationship (EDPVR)). The higher the Young’s modulus for a given strain, the higher the pressure needed to fill up the heart with sufficient blood volume – which thus explains the elevated diastolic pressures in a heart with diastolic dysfunction. A hypothesis is that the ratio between the Young’s modulus and the LV volume, as obtained for the lower right corner of the pressure-volume loop, is an accurate marker of the chamber compliance, and thus for the diastolic cardiac function. The presumed usefulness of this parameter, as extracted from the measurements of the natural shear waves, will be thoroughly evaluated by in-vivo tests on a porcine model.
Alberico will be working under the supervision of M.D. Verweij.