Circulation Time End Points

Ideal measurements are both simple and precise. The subjective circulation time has provided more simplicity than precision to three generations of physicians attempting to analyze cardiac function. Other more complex and less available measurements have displaced the circulation time from its prior vogue, probably because of the wide ranges of normal circulation time values. Yet, no other bedside measurement of cardiac function reflects both cardiac output and central blood volume with a single result. The peripheral arrival characteristics of radioisotope-labeled albumin are described in 15 normal subjects and in 13 patients with heart failure. These circulation-times are compared with the taste end point of the saccharin indicator simultaneously injected. Taste threshold, a variable not dependent on cardiac status, determines a significant proportion of the circulation time in both normal and failing circulations. The wide availability of instruments which measure radioactivity, dye density, or thermal change as a function of time could reinvest the circulation time with a new precision, in return for a modest loss of simplicity. Bypass of the noncardiac variable taste threshold may be added to the other well-described advantages of an objective circulation-time measurement by use of the time of half-peak concentration as the end point in recording the circulation time.