Factors influencing the accuracy of the cardiac output monitoring and diagnostic unit for pneumatic artificial hearts.

The Cardiac Output Monitor and Diagnostic Unit (COMDU) has been the most widely used method to noninvasively determine cardiac output in pneumatic ventricles for the past 10 years. Clinical observation has suggested a discrepancy between the COMDU and expected cardiac outputs. In vivo tests verified and quantified this error. The error sources were examined using in vitro test conditions, with both the inflow and outflow, as well as COMDU flow readings, being analyzed. Transducer and calibration error sources were also identified, and the accuracy of the method for determining cardiac output for the in vitro test conditions was quantified. With a more accurate calibration scheme, the in vitro average error was reduced from -16.2% (range of 0.1% to -41.1%) to 0.1% (range 4.8% to -3.65). The major error sources were identified as missed inflow, transducer calibration and drift, and system variance.