Infusion pumps are used in a broad spectrum of medical uses. For example, infusion pumps can be used to deliver nutrients to feed patients as well as medications, such as insulin, chemotherapy drugs, hormones, and opiates, to name just a few. Infusion pumps typically dispense liquids on a continuous, intermittent, and/or a patient controlled basis. One of the main advantages of infusion pumps is their ability to precisely dispense accurate volumes of fluid over long periods of time. To ensure accurate dispensing control, the pressure of the fluid needs to be tightly monitored.
High pressure conditions created by downstream occlusions or blockages in the patient's vein or kinks in the tubing of the infusion pump can be quite dangerous. Likewise, low pressure conditions created by upstream occlusions or lack of fluid can also be problematic. Occlusion detection systems have been developed in which a strain gauge in the pump detects the aggregate force to move the fluid through the entire system. However, the signal-to-noise ratio in these systems is quite poor, and current systems require a very high build up of sensed force in the system before a blockage is detected. These delays in detecting blockages can be very catastrophic.
Occlusion detection systems have been proposed in which the pressure is sensed along the tubing. For example, U.S. Pat. No. 7,121,143 to Malmstrom et al., which is hereby incorporated by reference, describes an optical pressure monitoring system in which a photodetector detects changes in the diameter of the tubing to in turn detect pressure changes by monitoring the amount of light obstructed by the tubing. However, the inventors of the present invention discovered such a system is prone to errors created by the optical properties of the tubing, the tubing's orientation, the liquid being pumped, and/or the ambient conditions. In addition, it was found that tubing with different elastic or other physical characteristics can be accidentally used, which can in turn create erroneous readings.
As another example, U.S. Pat. No. 6,110,153 to Davis et al., which is hereby incorporated by reference, describes an infusion device in which occlusions are detected by internally reflecting light within the tubing. The inventors similarly found this system to be prone to errors created by the properties of the liquid being pumped and by the tubing.
In different fields, other techniques have been proposed to detect pressure. For instance, U.S. Pat. No. 3,590,640 to Cindrich, which is hereby incorporated by reference, detects pressure changes by using optical interferometry to monitor the deflection of a diaphragm. However, it has been discovered that optical interferometry requires precise alignment and matching of the various optical components in order to produce real world accurate measurements, which is not practical in many medical environments.
Thus, there is a need for improvement in this field.