The regulation of stroke volume in the resting, unanesthetized dog

In the resting dog who displays a marked sinus arrhythmia, a model of stroke volume control was tested by a procedure of vectorial reconstruction. In the model, stroke volume is determined by preceding cardiac interval ( I), arterial pressure ( PA), and filling pressure ( PDV). The fit of the model is good; changes in stroke volume are accurately predicted by changes in the other variables. A unit-vector solution indicates the relative importance of each variable. A set of (regression) coefficients indicates how a change in each variable changes the stroke volume. Agreement from run to run and from animal to animal is good. All of the variables— I, PDV, and PA—are necessary to achieve the best prediction of the stroke volume. Each of the variables makes a unique contribution to the stroke-volume changes. If another variable acts in conjunction with those named, its effect is less than that of any of the others. Sympathetic discharge to the heart appears to cause no changes in stroke volume in these resting animals.