Custom Cable Proves to Be Key in Brain Wave Monitor

Originally Published MPMN June 2009

ENGINEERING SOLUTIONS

Custom Cable Proves to Be Key in Brain Wave Monitor

Bioconnect designed a patient cable to help harness brain waves amid environmental noise for an EEG device

Used in clinical settings to observe and quantify brain activity in patients, the NeuroSense monitor is a two-channel bilateral electroencephalographic (EEG) device with advanced signal processing capability. Manufactured by NeuroWave Systems Inc. (Cleveland; www.neurowavesystems.com), the product provides clinicians and researchers with an easy-to-use platform that can be rapidly deployed in any clinical setting.

Featuring low amplitudes of about 50 Vpp, brain waves serve as the source signals of the NeuroSense. Due to the uncontrolled environments in which the product is used, the EEG preamplifiers are designed to limit the effect of environmental noise. But to optimize the technology, an appropriate method to harness the source signals from the subject in the form of the patient cable was necessary.
Because the product’s need for noise reduction was demanding, contrary to most clinical EEG systems, the company opted to use shielded electrode leads instead of conventional leads. NeuroWave Systems sought to minimize triboelectric noise as well. Furthermore, to limit potential connection errors and provide users with a virtually tangle-free system, the cable design consisted of varying electrode lead lengths. As a result, however, the coupling capacitances between each signal lead and the ground lead were unbalanced. Consequently, the common mode rejection ratio of the amplification chain was reduced to suboptimal levels.
Upon realizing that an off-the-shelf patient cable could not meet such demands, NeuroWave Systems selected Bioconnect, a div. of RF Industries (San Diego; www.biocables.com) to create a custom solution. The supplier was tasked with the design of the cable, the design of the mold, and the overmolding of the cable. Bioconnect accepted this challenge and set out to design a mold that could house the electronics and the shield while maintaining a low profile.
“The NeuroWave project presented many challenges from a molding standpoint,” recalls Floyd Henry, Bioconnect manufacturing engineer. “We had to protect the electronics from the adverse effects of molding forces, create good, functional strain relief on all of the lead wire and cable components, make the design aesthetically pleasing, and maintain as small a profile as possible on the finished device.” After just a single iteration and a couple of sample trials, the overmolding method was finalized and ready to be launched into production.
Physical criteria also had to be factored into the cable’s design. Unobtrusive and flexible, the cable had to be robust and resilient to the harsh environment of operating rooms and ICUs. In its daily use, the cable had to withstand being stepped on, pulled, rolled over, and subjected to chemicals. And yet it still had to reliably measure tiny microvoltages during neuro and cardiac surgeries while protecting the patient and the clinical staff in the event of a high-voltage cardiac defibrillation.
“That’s a lot to expect from a cable, yet that is precisely what Bioconnect delivered,” says Stephane Bibian, technical director, NeuroWave division. “The patient cable is a critical key accessory of the NeuroSense monitor, and its quality defines the overall performance of the system as a whole.”
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