Preliminary testing of TENS unit placement

Author: Emma Paulus | Major: Mechanical Engineering | Semester: Spring 2024

During the spring 2024 grant term, I worked alongside my mentor, David Paulus, to investigate how expectation can influence the perception of pain.  Our primary goal was to determine if verbal and visual affirmation of anticipated pain levels influenced how soon and intensely pain is felt. Participants were randomly assigned to one of two groups: high expectation (group 1) or low expectation (group 2). A transcutaneous electrical nerve stimulation (TENS) unit was used to induce low levels of discomfort/pain. Understanding how expectation affects pain threshold (time until they first felt pain), tolerance (total minus threshold) and perception has the potential to ease the pain patients experience with a lessoned reliance on opioid painkillers.

This research originally began as an honors project for my industrial engineering statistics class during fall 2023. I explored previous studies on pain perception, most of which been conducted by using skull caps to look at brain activity but did not focus on participants’ perceived pain levels. This inspired me to measure the individual perception of expected and experienced pain. Unfortunately, delays in obtaining IRB approval prevented me from using this research for my statistics project, but I was determined to continue my research.

There are many ways to induce low levels of pain for research, one of the most common is a cold pressor test. In this test participants place their hand in cold water until it becomes unbearable or until they have reached a safety time cap. However, in many cases the time cap is much lower than patients’ pain tolerance leading to inconclusive results. Because of this, I opted to use muscle stimulation to induce low levels of discomfort. After testing several TENS units, we decided to use an Auvon TENS unit with electrode pads placed at the start and end of the bicep, thanks to the guidance of Dr. Eric Specking, Dr. Paulus, and my research partner, Aidan Donoho.

Due to the phycological impact and the use of TENS units, safety was a very important factor we had to consider. All participants were over 18 and required to sign an informed consent form before participating in the study. Those who were pregnant or there’s a chance they might have been pregnant, had epilepsy or a heart problem, or had an overactive bladder were not allowed to participate in the study. A medical professional was also present to provide medical supervision during all testing. Furthermore, the TENS units had a current limiter and the test immediately ceased after participants had reached their pain tolerance or 300 seconds had elapsed from when the test began.

I was very grateful to have support from the industrial engineering department during this research, Mr. Brandon Crisel and Dr. Paulus offered their students extra credit to participate or volunteer, resulting in 54 participants and 5 volunteers.

The findings revealed that gender and bicep diameter had a significant effect on pain threshold and tolerance. Expectation also influenced the perception of pain in men. Men with low pain expectations reported a significantly higher level of pain felt than those expecting high levels of pain. It was also found that expectation played a large role in the pain threshold and tolerance of women, those with low expectation of pain had a significantly higher pain threshold and tolerance.

After completing the research, I attended the Rocky Mountain Bioengineering Symposium in New Orleans, Louisiana, to present my findings with my co-researcher, Aidan Donoho. At the symposium, I was able to meet many experts in the fields of bioengineering and biomedical engineering who advised me on various aspects of my research, including potential future directions, and addressed the limitations of my initial study. I also attended presentations on cutting-edge advancements that expanded my understanding of pain mechanisms and other sectors of bioengineering. Furthermore, the symposium provided valuable opportunities to enhance my public speaking skills and connect with peers on a personal level.

In the future, I plan to expand my research, potentially using balance as a factor to determine how back pain can affect balance. I plan to research how weight is distributed while walking and standing with back pain, and if changes in expectation and environment influence this.