Abnormal Indicator Dilution Patterns in Dogs Produced by Flowmeter Probes on the Pulmonary Artery.

• Indicator dilution technics have been employed by Malooly and co-workers J for the in vivo calibration of electromagnetic flowmeter probes. In attempting to apply this calibration procedure to the measurement of pulmonary arterial flow in anesthetized dogs, we noted that the presence of the flowmeter probe on the pulmonary artery was frequently associated with abnormal indicator dilution curves. In 16 out of 32 experiments the indicator dilution curves were so abnormal that they could not be used to calculate flow as required for calibration of the flowmeter probes. The abnormal curves resembled those observed in the presence of left-to-right shunts; typical examples are shown in figure 1. The possibility that slight constriction or immobilization of the pulmonary artery could interfere so drastically with normal distribution of dye seemed to warrant further investigation. The following experiments show clearly that mechanical interference with the pulmonary artery, incident to placement of electromagnetic flow probes around the artery, can indeed produce striking abnormalities in indicator dilution curves recorded at the femoral artery.