Ventricular interdependence and the transient response of the left ventricle to inspiration: a model study.

A mathematical model of the circulation was developed and used to study the transient variations in ventricular volumes with inspiration. The contributions of increased left ventricular afterload, ventricular interdependence, and reduced pulmonary venous flow to the initial decrease in left ventricular stroke volume were examined. Heart rate was kept constant. Right ventricular end diastolic volume increased rapidly, but transiently, with inspiration. Ventricular interdependence affected left ventricular function; it increased the magnitude of the decrease in left ventricular stroke volume, reduced the corresponding increase in end systolic volume, and appeared to be responsible for an initial decrease in end diastolic volume. Despite a 10% pooling of blood in the pulmonary circulation the decrease in pulmonary venous flow was small. It is suggested that the decrease in left ventricular stroke volume is caused both by the reduced intrathoracic pressure, which increases the afterload on the left ventricle, and by the increase in the diastolic elastance of the left ventricle caused by the increase in right ventricular volume (ventricular interdependence). The increased afterload reduces the effective ejection pressure, decreases the stroke volume, and increases the end systolic volume. The increase in left ventricular diastolic elastance, secondary to the increase in right ventricular volume, further reduces the stroke volume by increasing the left ventricular diastolic pressure at a given volume and thus decreases the end diastolic volume.