Beat-by-Beat Stroke Volume from Aortic-Pulse-Pressure Analysis

A formulation for determining stroke volume from arterial pressure is presented which differs from previous methods in both scope of application and theoretical basis. The formulation is specifically applicable in the presence of large successive beat-to-beat variations which occur with premature contractions and other arrhythmias. Its derivation is based upon Windkessel theory, as are most others, but special emphasis is placed upon analysis of diastolic pressure (when arterial dynamics most nearly approach characteristics assumed in Windkessel theory). The formulation contains no ad hoc parameters although mean peripheral vascular resistance must be known and redetermined when changes in resistance occur. Results from eight animal experiments are presented which indicate that this formulation predicts stroke volume to about ten-percent (10-percent) error over successive beat-to-beat changes of severalfold during episodes of mechanically induced beats and during control, isoproterenol, and angiotensin administration.