Cardiovascular responses to intrathoracic pressure variations in coronary disease patients: a computer simulation.

Several studies have suggested that the Valsalva maneuver may predispose potential lethal arrhythmias in patients with coronary artery disease, since this maneuver induces diminished coronary flow. On the other hand some studies have suggested that the Valsalva maneuver abruptly reduces determinants of cardiac oxygen demand, relieving angina pectoris. In order to study the variations of the myocardial oxygen supply-demand relation, during different applications of the maneuver, a mathematical model of the human cardiovascular system is presented. The model has been submitted to an evaluation process allowing the inclusion of a number of additional refinements to the mathematical model structures, and the obtaining of a reduced model in order to improve the computer time and parameter estimation of the simulation. The simulated output variables of the model correlate well with in vivo data obtained from ten patients with typical exertional angina pectoris studied during cardiac catheterization. The evaluation of the cardiac catheterization data has allowed the differentiation of two subsets of patients by the identification of two different coronary controllers. Computer simulation has permitted the analysis of the relative influences of the intrathoracic and intraabdominal pressure variations on the cardiovascular variables. Depending on the coronary control of the patients, the simulation results have shown that the myocardial oxygen supply-demand relation, calculated during the simulation of high intrathoracic pressures, long duration Valsalva maneuvers, or two consecutive maneuvers, gets values higher or lower than unity. These results suggest, respectively, beneficial or detrimental cardiac effects on the patients.