1. POLYTECHNIC OF TURIN
Abstract
Biomedical Engineering
Polytechnic of Turin
Master Degree
A proposal for the in vivo evaluation of venous distension as a
surrogate marker of heart failure
by Leonardo Milizia
The monitoring of the functionality of the heart in patients affected by heart failure (HF) still requires
hospitalization. For this reason, novel approaches and monitoring procedures are needed in order to
optimize the follow up of HF patients by increasing screening potency, preferably with independent
methods. This would lead to a more effective prediction of cardiac failure with the consequent
prevention/minimization of hospitalization. An impaired ventricular pump function leads to an excessive
fluid overload in the pulmonary and peripheral system. A common consequence for this, in order to
maintain pump function, is an elevation in venous blood pressure, which is related to a distention of the
veins, due to the elastic behavior of the vessel wall. According to this widely observed phenomenon, it was
conjectured that the degree of venous distention could be used as a surrogate indicator of fluid overload
and, ultimately, of cardiac failure.
The present study investigates the feasibility of a new application which, from the estimation of the cross
sectional area (CSA) of large veins, as obtained by catheterization with a chronic four electrodes
conductance catheter. In detail, an estimation of the resistivity from intravascular catheter measurements
was obtained by applying schemes developed for geological application. The resistivity values were then
related to heart failure. A computational model, and in-vitro model and an algorithm were developed in
order to get more insight in the relationship between venous distensibility. In particular, the infinite
elements computational model was developed to mimic the in-vivo condition of a catheterized large vein,
where a static electric field, originated in consequence of the tension at the electrodes of the catheter, was
simulated inside the vessel. The output from the computational study, e.g. the voltage from pick-up
electrodes voltage, was used as an input of the developed venous distension algorithm (VDA), which gives
as output the resistivity of the blood and the radius of the vein. The VDA, was validated by means of an
in-vitro model, an operational platform mimicking a the physiological environment. In detail, the catheter
lead was positioned inside a balloon to mimic the venous distension. Saline solutions with different
conductivity were injected inside the balloon to simulate the enlargement of the vein. Animal blood was
also used in the balloon to check the behavior with true blood. The application of the VDA to in vitro
data resulted in a maximum error of 2,5% in the estimation of the radius of the vessel, both when the
catheter leads were positioned at the center or near the vessel to a particular distance. This maximum
distance close to the vessel is determined from the electrodes configuration. The present study
demonstrates that a novel approach, based on (1) chronic catheterization of a large vein by using a four
electrodes catheter and (2) an ad hoc algorithm modeling the relationship between resistivity of the medium
and vessel wall, allows for a reliable estimation of venous distensibility, an indirect measure of HF. The
preliminary in vitro tests demonstrated that the VDA can be used for this purpose.