Bioconnect NeuroSENSE

Measuring and quantifying brain waves: the NeuroSENSE Monitor

by Stephane Bibian and Tracie Capozzio
NeuroWave Systems Inc., Cleveland, Ohio, USA

NeuroWave Systems Inc., an Ohio-based medical device manufacturer, introduced the NeuroSENSE Monitor at the 2008 American Society of Anesthesiology meeting in Orlando this past October. The NeuroSENSE monitor is a 2-channel bilateral electroencephalographic (EEG) device with advanced signal processing capability intended to be used in clinical settings to observe and quantify brain activity in patients, and thus further the understanding of the patient’s neurological state. The NeuroSENSE provides clinicians and researchers with an easy-to-use platform that can be rapidly deployed in any clinical setting, such as Intensive Care Units, Operating Rooms, and Emergency Units. The NeuroSENSE monitor and its disposables and accessories are not FDA cleared and are not yet offered for sale.

Electroencephalograms (EEG), or brain waves, are the source signals of the NeuroSENSE. These signals are typically of very low amplitudes (about 50 μVpp). To the untrained eyes, they look like random noise, and are particularly sensitive to physiological artifacts like muscle noise and environmental interferences. Due to the uncontrolled environments in which the NeuroSENSE is to be used, the EEG pre-amplifiers are designed to limit the effect of such environmental noise. Special shielding and front-end active filters have been integrated to an ultra-low noise amplification chain. In addition, a number of features have been added to improve the overall robustness of the system: gas tube discharge for cardiac defibrillation proofing, tone generator for continuous impedance measure, electro-surgical interference filters and detector, a 6 kV isolation barrier, etc. These features are the NeuroSENSE first line of defense against environmental noise and radio-frequency interferences.

In addition to these advanced hardware features, the NeuroSENSE integrates state-of-the-art processing algorithms to detect and remove physiological artifacts (e.g., eye movements and blinks) that commonly corrupt the EEG signals. The cleaned EEG signals are then processed and displayed to the clinician. The main processed EEG variable is the WAVCNS index, which quantifies brain patterns in an easy to understand scale from 0 to 100, where 100 indicates an awake activity level, and 0 indicates a complete absence of brain activity. The WAVCNS index was developed to aid in assessing the effects of anesthetic drugs on the patient’s brain. Even with the most sophisticated algorithms and highest quality electronics, without an appropriate method to harness the source signals from the subject, the NeuroSENSE technology would be limited at best. Thus very early in the design, the NeuroSENSE engineering team identified the patient cable as a key component of the design. Since our needs for noise reduction were demanding, contrary to most clinical EEG systems in the field, we decided to use shielded electrode leads instead of conventional leads. An additional requirement was to minimize triboelectric noise.

However, standard off-the-shelf patient cables were not able to meet our requirements. In particular, our design involved different electrode lead lengths to limit potential connection errors and provide users with a virtually tangle-free system. As a result of the varying lead lengths, the coupling capacitances between each signal lead and the ground lead were unbalanced. Consequently, the excellent common mode rejection ratio of the amplification chain crumbled to suboptimal levels, which was unacceptable for our application. This unanticipated problem could have resulted in a serious delay in the overall project time line. Thus, we needed to rapidly design a specific electronic board to rebalance the capacitive coupling between the ground and the leads by adding very small capacitor in parallel across the leads. In addition, we also needed to shield the electronics to prevent electrostatic discharge when handling the yoke, while maintaining the large high impact cardiac defibrillation resistors. And all this needed to result in a small form factor, thin profile and slick look. As one can imagine, this required a complete customized solution which needed to be developed within few weeks and without room for errors or iterations. We needed to get it right the first time and on time in order to meet our deadlines!

We embarked on investigation of a number of suppliers of patient cables. Finally, we selected Bioconnect due to their extensive experience in the field. In particular, Mr. Floyd Henry was ready to give us a hand. Mr. Henry personally took on our challenge and set out to design a mold that could house the electronics and the shield, while maintaining a low profile. After just a single iteration and a couple of sample trials, the overmolding method was finalized and ready to be launched into production. Our deadlines were met, the yoke looked great, and our customized solution satisfied all of our requirements.

The patient cable is a critical key accessory of the NeuroSENSE and its quality defines the overall performance of the system as a whole. In addition to being unobtrusive and flexible, it must also be robust and resilient to the harsh environment of operating rooms and ICUs. In its normal day-to-day use, the cable will be stepped on, pulled, rolled over, and subjected to chemicals. Yet, it will have to continue to reliably and faithfully measure tiny micro-volt voltages 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 Floyd and his colleagues at Bioconnect delivered.

On behalf of the NeuroWave team, we would like to thank Bioconnect for their help, expert advice and dedication. And, above all, thank you for the quality of the cables you built for us!