2.3.1. Electromagnetic Compatibility

The shoulder coil that is worn by the study participant creates a radiofrequency magnetic field that is used to provide power and command signals to the implanted device. One common concern with this device and other medical devices that utilize electromagnetic energy is exposure of the study participant to this energy. However, previous studies have shown that radiowaves as well as other types of electromagnetic radiation are not associated with significantly increased incidence of disease or tissue damage, even at doses much higher than those used in the present study. For example, magnetic resonance exposure of mouse and chick embryos did not affect the birth dates, birth numbers, or cause abnormal development (Yip et al, 1994; Frolen et al., 1993; Wiley et al., 1992; Margonato, et al., 1995); Exposure of adult baboons to 60Hz electromagnetic field exposure had no effect on their performance in accomplishing a complex task (Orr et al., 1995). To support further the literature (under the special conditions of the specifically tuned magnetic coil in the shoulder pad), a study was conducted at Queen’s University in Kingston, Canada to test the safety of a magnetic field used to transmit power and data to microstimulator devices.

Test Description

Sixteen mice (8 weeks old) were randomly separated into two equal sized groups and caged. Each cage was enclosed in a magnetic coil. The control group had an inactive coil, whereas the experimental group had a coil that transmitted EMF radiation continuously for the duration of the test period. The magnetic field to which the mice were exposed was similar to that which will be used for the clinical studies: a 2MHz sinusoid with 0.5 amperes of current through 10 turns of wire wrapped in a helical coil, 10 diameter, 15 long. Both groups of mice were fed and given water ad libitum in a room in which air temperature was held at 23C and a light cycle of 12 hours on, 12 hours off was used. Mice were then sacrificed after 3 months of coil exposure. Necropsies were performed to detect any ill effects due to magnetic field exposure. Blood tests and necropsies were conducted on the mice under blinded conditions by a non-partial veterinarian (Dr. Michael Shunk, Animal Care Services, Queen’s University Kingston).

Test Results

blood smear tests - Mice in both groups were tested for abnormal white blood cell counts. Counts of lymphocytes, neutrophils and eosinophils were within normal range and did not differ significantly between the two groups.

Autopsies - All mice were subjected to an exhaustive autopsy by the certified veterinary pathologist. Organs were examined for abnormalities. There were some variations in organ features but their occurrence was not statistically correlated with the EMF conditions under which they were raised, and were judged by the inspecting veterinarian to be typical of normal variations in animal health. No tumors were observed in any of the mice.

2.3.2. Stress Tests

Stress testing is defined as testing designed to increase the likelihood of failure by subjecting the sample to conditions that will accelerate the occurrence of failure. In preliminary tests, a three-point bending test was initially performed on glass capsules. A more complicated test was subconsequently conducted to model how external forces, such as sudden accidental impact applied to overlying soft tissues, might be conveyed to an embedded microstimulator. A summary of the test results follows. Detailed test results can be found in Appendix 5.