Left ventricular function described in physical terms.

• The first step in any physiological investigation is to define the problem. If this definition is ambiguous, the experimental results will most probably be inconclusive or may even prove irrelevant. To secure conclusive results, the investigator must select appropriate variables for measurement. Ideally, the terms comprising the definition of the problem should be sufficiently precise to enable him to identify these essential variables automatically. For example, if the problem centers around the work performed by the ventricular chamber, the variables to be measured are directly indicated by the physicists' definition of "work." On the other hand, a problem of cardiac function couched in terms of changes in "contractility" would be approached differently in different laboratories, according to the local interpretation of the term. Since "contractility" is variously employed to indicate "vigor" of contraction, rate of ejection, degree of ejection, rate of rise in ventricular pressure, or slope of a "function curve," what physical variables should be measured to determine whether this property has been altered under a specific experimental condition ? The significance of changes in the performance of the heart would be more clearly understood if they were described in precisely denned terms of the sort used by physical scientists and engineers. To this end, variations in the performance of the left ventricle in intact conscious dogs have been analyzed