Noninvasive assessment of cardiovascular health

Abstract

Cardiovascular health is currently assessed by a collection of hemodynamic parameters many of which can only be measured by invasive methods often requiring hospitalization. A non-invasive approach of evaluating some of these parameters, such as systemic vascular resistance (SVR), maximum left ventricular elasticity (ELV), end diastolic volume (VED), cardiac output and others, has been established. The method has three components: (1) a distributed model of the human cardiovascular system (Ozawa) to generate a solution library that spans the anticipated range of parameter values, (2) a method for establishing the multi-dimensional relationship between features computed from the arterial blood pressure and/or flow traces (e.g., mean arterial pressure, pulse amplitude, mean flow velocity) and the critical hemodynamic parameters, and (3) a parameter estimation method that provides the best fit between measured and computed data. Sensitivity analyses are used to determine the critical parameters that must be allowed to vary, and those that can be assumed to be constant in the model. Given the brachial pressure and velocity profiles (which can be measured non-invasively), this method can estimate SVR with an error of less than 3%, and ELv and VED with less than 10% errors. Measurements on healthy volunteers and patients were conducted in Brigham and Women's Hospital, Boston, MA. Carotid, brachial and radial pressures were measured by tonometry and velocities at corresponding locations were measured by ultrasound. Reasonable agreement is found between the measured pressure and velocity curves and the reconstructed ones. Invasive measurements of hemodynamic parameters are available for two of the patients, which are compared to predictions to evaluate the performance of parameter estimation routines.