measure the contractile effects of digitalis in man. Ideally, one would desire to achieve that level of digitalization that would produce the maximal increase in the force of contraction without inducing arrhythmias or other manifestations of overdosage.Various techniques have been utilized to measure the positive inotropic response to digitalis glycosides. The rate of rise of the left ventricular pressure (dpjdt),1 the force of contraction produced by the Walton Brodie Strain gauge arch attached to the ventricle, 2, 3 and the duration of the phases of ventricular systole4 are the usual parameters used by investigators.The purpose of this study was to test in man the reliability of the measurement of changing cardiac contractility as evidenced by changes in the first derivative of the upstroke of the arterial pressure curve and the systolic time intervals. The maximum brachial artery first derivative was used rather than the left ventricular dp/dt because of the relative ease in obtaining this measurement. However, it is recognized that since the maximum dp/dt occurs before the onset of ejection, the brachial artery first derivative may not necessarily reflect the first derivative of the ventricular pressure during the isovolumic phase.In addition, changes in the force of contraction were measured in normal dogs and in dogs with spontaneously acquired mitral insufficiency. These indices of the therapeutic effect of digitalis were then analyzed to see if they would provide an objective basis for digitalization.
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