The accuracy of a disposable blood pressure transducer (DBPT) is determined by its physical properties: natural frequency (NF) and damping coefficient (DC). We planned this study to investigate whether the NF and DC of a DBPT are altered by attaching extended catheters and evaluated changes of these physical properties over time.

Fifteen DBPT sets were connected to a monitor and recorder set. These sets were divided into three groups; five sets had catheters of normal length (Group 1), five sets had 50 cm extended catheters (Group 2), and five sets had 100 cm extended catheters (Group 3). The NF and DC of each system were measured using the fast flush (FF) test. After the DBPT sets were installed, the FF test was performed for each group at five time intervals: 4, 24, 48, 72, and 96 hours.

The NF of Groups 2 and 3 decreased and their DC increased compared to those of Group 1. Whereas the NF of Group 3 increased over time, those of Groups 1 and 2 did not. The DC of Groups 2 and 3 decreased over time, but remained unchanged over time for Group 1. When the FF test was done at intervals longer than 24 hours, it was found that the NF, but not the DC, increased for all groups.

Attention should be paid to interpret blood pressure using DBPTs measured by extended catheters and using DBPTs for long periods of time without FFs.