Methods to improve the signal-to-noise ratio during the recording of biological signals

During high risk surgeries we use various electrophysiological tests (i.e., EEGs, EMGs, EPs) to monitor the functional integrity of neurological structures that are at surgical risk. If data demonstrate a significant change the surgeon is warned and intervention is initiated thereby avoiding or minimizing the effects from a postoperative neurological deficit. Because the sooner intervention is initiated the more effective it is we need the monitoring procedure to be as sensitive to the onset of an insult as possible. One type of test we administer is a sensory based evoked potential (EP). This response is elicited by stimulating a peripheral end organ, such as a peripheral mixed nerve using an electrical shock or the ear using a clicking sound, and recording the action potential (AP) at multiple sites as it progress from the periphery to the brain. Because each response is so small in amplitude (voltage) compared to ongoing random noise, narrow band filters, specific time bases, and an averaging computer are used to improve the signal to noise ratio (SNR). While these methods will work, they increase the time needed to record and analyze a measurable response which decreases the efficacy of intervention in the event data demonstrate a significant and potentially pathological change. For example, to record a somatosensory evoked potential (SEP) will require 200-300 data samples be recorded before an averaged response is obtained. This will take over 3-4 minutes which significantly decreases the sensitivity of the test to the onset of a surgical insult.
Our goal is to evaluate different methods to improve the SNR so that data can be collected more quickly, thereby improving the sensitivity of the monitoring to the onset of a surgical insult. Additionally, the quicker we can record a response the easier it is for the surgeon to identify which surgical maneuver deleteriously affected the nerve and then modify his approach for that patient or the next one. If we can record a response in 3-4 seconds the sensitivity of monitoring to the onset of an surgical insult is improved significantly, which will increase the efficacy of intervention, and ensure a more favorable surgical outcome.

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