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A dynamic balloon volume sensor system (DBVSS) was designed for use with the intra-aortic balloon pump (IABP), a therapeutic device to assist heart recovery after cardiac dysfunction or cardiac trauma, and the Pittsburgh respiratory support catheter (RSC), an internally deployed gas exchange device which augments lung function. The DBVSS was designed to detect the degree of inflation of the balloons incorporated into each device as they pulse within a patient. Both devices require full inflation for optimal performance, and both will under-inflate during normal operation. The sensor system requirements were to measure volumes within 10% of the actual across the range of expected pulsation frequencies as well as in changing concentrations of helium.
The DBVSS employed a hot wire anemometer to detect the flow entering the balloon, combined with a computer algorithm to integrate the flow to find volume. The system compensated for the flow reading changes resulting from changing helium concentration by measuring gas properties during zero gas flow between pulsations, and used this data to correct the flow profile at each helium concentration. The volume from the DBVSS was compared to the volume standard as measured by water displacement in a plethysmograph.
The system was able to accurately measure delivered balloon volume under changing gas composition as well as detected volume loss from the balloon across helium concentrations. The DBVSS measured the volume within 10% across these tests, as well as under compression of the balloon, high resistance in the driveline and across frequencies up to 480 beats per minute. The DBVSS was proved to be within the design requirements for helium concentration and inflation methods for both the devices considered.