Measurement of Impact Loads Applied to an Implanted Drug Pump Connector in a Porcine Cadaver Specimen

[+] Author and Article Information
Thomas C. Bischoff

 Medtronic Neurological, 800 53rd Avenue NE, MS N363, Columbia Heights, MN 55421thomas.c.bischoff@medtronic.com

Marty D. Martens

 Medtronic Neurological, 800 53rd Avenue NE, MS N363, Columbia Heights, MN 55421marty.d.martens@medtronic.com

Matthew H. Adams

 Medtronic Neurological, 800 53rd Avenue NE, MS N363, Columbia Heights, MN 55421matthew.adams@medtronic.com

William J. Gallagher

Department of Surgery, University of Minnesota, B172 Mayo, MMC 107, 420 Delaware Street SE, Minneapolis, MN 55455galla009@umn.edu

Paul A. Iaizzo

Departments of Surgery and Physiology, University of Minnesota, B172 Mayo, MMC 107, 420 Delaware Street SE, Minneapolis, MN 55455iaizz001@umn.edu

J. Med. Devices 1(2), 119-125 (Mar 20, 2007) (7 pages) doi:10.1115/1.2736398 History: Received April 01, 2006; Revised March 20, 2007

Anecdotal and documented reports from both patients and doctors have described unanticipated breaks in connections between implanted catheters and drug pumps. In extreme cases, such disconnections in patient-required therapies could result in either withdrawal symptoms or possible deaths. Patients typically attribute such device failures to falls or impacts associated with vigorous physical activity; subsequent failure analyses most often have indicated pump connector uncouplings. We fabricated a facsimile of the Medtronic®SynchroMed® II pump that included both an accelerometer and a force sensor. The force sensor measured forces imparted on the pump connector via the attached catheter and surrounding tissues. The test pump was implanted in the lower left abdominal areas of porcine cadavers in various orientations. Wire-reinforced catheters were tunneled for 2025cm under the abdominal epidermis, anteriorly toward the head, and the non-connector pump ends were secured by sutures. Following each simulated implant, the cadaver specimens were loaded into a harness and hoisted to a height where either their buttocks or backs were 8086cm above the floor, simulating a worst-case scenario in which a patient might have fallen down a flight of stairs or off a step stool. The cadavers were then quick released from the hoist attachment, while forces (X, Y, and Z) and accelerations (X, Y, and Z) versus time were simultaneously recorded. Six porcine cadaver specimens were utilized for a total of 72 trials. Subsequent Monte Carlo analyses allowed us to model the variation in stress imparted onto the pump connectors and the estimated variation of the pump connector strength, as a means of predicting required connector retention impact specification for future designs. The recorded forces applied onto the connectors, including data from all three connector axes (X, Y, and Z), were typically within the range of 4.59N. However, in several trials, applied forces ranged as high as 3049N. Monte Carlo modeling provided a maximum resultant load specification of 100.4N for a 0.033msec duration. Based on this value, due to predicted impact events, subsequent failures of future designs would be estimated at 7ppm. Based on our data, a new design requirement has been generated to ensure that implantable drug pump connector assemblies will, in high probability, perform their intended functions.

Copyright © 2007 by American Society of Mechanical Engineers
Topics: Force , Design , Pumps , Drugs , Stress , Catheters
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Figure 4

This plot begins on the left with data from run 1 (drops 1–24), in the middle are data from run 2 (drops 25–48), and on the right are the data plotted from run 3 (drops 49–72)

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Figure 5

Each data point represents the average of nine values, i.e., averaged data obtained from each of the three different porcine cadaver studies

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Figure 6

Samples 114 and 77 (run 1) represent experiments 1–4 and 5–8, respectively, and samples 66 and 69 (run 3) represent experiments 1–4 and 5–8, respectively. Note that samples 66 and 114 display the most variability in data and both samples were used in the exact same experiments.

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Figure 7

Data represent recorded peak accelerations plotted relative to each identified experimental factor

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Figure 8

Waveforms generated from a typical release/impact trial; data indicate the standard shape of applied force that would be needed for the design of appropriate testing systems

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Figure 9

Plotted are the durations of the calculated applied forces. The lines indicate the 95% confidence limits for the derived probability plot.

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Figure 1

Facsimile of the Medtronic®SynchroMed® II made using stereolithography rapid prototyping technology. Force sensor and accelerometer are visible through the test pump body. Pump axes and pump connector locations are shown.

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Figure 2

Cadaver with subcutaneous implanted test pump in lower left abdomen is shown. Sensor cabling and catheter locations are noted.

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Figure 3

Experimental configuration schematic shows pump location and orientation with respect to cadaver upper and lower extremities. Three of the four experimental factors are shown: pump orientation, pump suture location, and catheter suture location.



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