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People with epilepsy have an increased risk of mortality when compared to the general population. These increased mortality risks include deaths related to status epilepticus and sudden unexpected death in epilepsy (SUDEP). Physiological data describing cardiac, respiratory, and brain function prior to sudden death in epilepsy is crucial to the studying the underlying mechanisms behind these deaths. Because it is unknown when sudden deaths in epilepsy may occur, continuous monitoring is necessary to guarantee the capture of physiological data prior to death. I have used custom designed implantable devices to continuously measure cardiac, respiratory, and neurological signals in freely behaving rats with chronically induced epilepsy. Due to the continuous respiration measurements, the resultant dataset is the first of its kind. This dataset indicates that respiratory abnormalities (reduced respiration and short apneas) occur during and after seizures. These abnormalities may indicate SUDEP onset because obstructive apneas due to laryngospasm have been indicated as possible causes of SUDEP in other studies. Laryngospasms can be caused by gastric acid coming into contact with the larynx. During a laryngospasm, intrinsic laryngeal muscles contract, resulting in the closure of the airway. Recently published research has indicated that acid reflux may be responsible for triggering fatal laryngospasms in rats with induced seizures. I have found that the larynx can be opened during a laryngospasm by electrically stimulating the recurrent laryngeal nerves. I have also found that performing gastric vagotomies leads to a statistically significant reduction in mortality due to fatal apneas in rats with induced seizures.

Implantable devices are ideal for recording biological signals in animal models as they have minimal effect on the animal’s normal behavior during observation. The creation of the circuitry for an implantable device has several restrictions including size, power consumption, and noise reduction. These factors compete against each other, making it necessary to carefully optimize circuit components for a given application. This study evaluates the design of a four-channel analog front end circuit board to record cardiac, neural, and respiratory biological signals. Through a critical analysis of component specifications for the circuit’s components and an evaluation of the circuits’ power and noise performance, the ideal analog front end for the implantable biological recording device was designed. The combination using components AD8235 and OPA2348 decreased noise, power consumption, and size by 43%, 58%, and 57% respectively without significantly impacting other metrics. This combination was chosen to best improve the performance of the implantable device.

Respiratory measurements can be used as diagnostic and research tools. Spirometry is the gold standard for gaining these measurements, but is difficult to use in rodents as it requires an invasive procedure. Total Body Plethysmograpy (TBP) is a non-invasive way to measure respiration rates that does not cause stress to the rodent. In this system, the subject is encased in a solid, constant volume chamber with measurements determining the subject’s respiration. When using TBP in medical or research settings, challenges occur in powering devices within the TBP chamber as wires and other recording equipment compromise the airtightness of the chamber. Therefore, it is imperative to create a TBP chamber that provides wireless power for these purposes. To do so, subjects were placed in a cubic or cylindrical airtight chamber with one inflow and exhaust nozzle to control chamber pressure and provide a steady stream of fresh oxygen. Pressure readings from the inside of the chamber were taken at a rate of four samples per second. Tests were run from two minutes to three hours to encompass rodent activity. Tests were inconclusive for measuring respiration with the specific sensors used, and further research and testing is needed to perfect this method. Once the method is proven to work with the pressure sensors, it will be able to be paired with the MRC chasm and therefore implemented in other studies.