Thoracic-Aorta Flow in Man

¹ From the Section of Physiology, Mayo Clinic and Mayo Foundation, Rochester, Minnesota

A technique is described that permits the continuous determination of the thoracic-aorta flow in man by the injection of Evans blue (T-1824) at a constant rate into the thoracic aorta, with continuous recording of the resulting concentration of the indicator in blood flowing from the femoral artery. By simultaneous sampling from a radial artery, the concentration of recirculating indicator can be determined, making it theoretically possible to measure thoracic-aorta flow for any duration of injection desired. Complicating problems of obtaining uniform mixing and a generalized vasodepressor reaction believed to have resulted from hemolysis produced by high-energy jet streams used to promote mixing were encountered. Evidence is presented indicating that uniform mixing of blood and indicator, basic to the application of indicator-dilution techniques, was obtained. Thoracic-aorta flow was measured nearly simultaneously with total cardiac output in 15 paired determinations performed on eight subjects. The thoracic-aorta flow index ranged from 1.2 to 1.9 (mean of 1.5) liters per minute per square meter of body surface. The cardiac-output values determined by the direct Fick method exhibited greater variability, ranging from 2.3 to 5.6 (mean of 3.6) 1/min/m.² The coefficients of variation were 12 and 28% for the thoracic-aorta flow and cardiac indexes, respectively. It is concluded that the constant-rate injection technique, especially when provision is made for quantitation of recirculating indicator, provides a satisfactory method for the continuous measurement of thoracic-aorta flow in humans.