DVT Prevention Pedal

Summary

What sparked my interest in deep vein thrombosis (DVT) was the news that Serena Williams was admitted to the emergency room because of a pulmonary embolism. Pulmonary embolism is a fatal consequence of DVT, which is a blood clot that originates in the deep vein of the leg. DVT affects ~1 million Americans and kills more people than AIDS, breast cancer, and motor vehicle accidents combined [1-3]. The economic burden of DVT is ~10 billion dollars annually [4]. A major preventable cause of DVT is immobility [5]. I became concerned that my grandparents would be at risk for DVT because they endure long air-travel to visit us. This inspired me to design a simple, portable DVT Prevention Pedal. In contrast to the currently available DVT prevention products that use the principle of compression, my design uses resistance, which has been shown to be better at improving blood flow [6]. I tested my device in human subjects, using electromyography (EMG) and found that muscle activity while using the pedal was comparable to that of walking. Additionally, I created a portable EMG sensor that can be connected to a mobile device, to enable the user to monitor muscle activity while using the pedal. In the future, I plan on testing an upgraded device with variable resistances in a larger population and measure blood flow using Doppler ultrasound. In conclusion, I was successful in creating a simple, portable, device that increases muscle activity, which can help prevent the risk of DVT.

Summary video

Question / Proposal

Deep vein thrombosis (DVT) is a blood clot that occurs in the deep vein of the leg. The clot can dislodge and travel to the lung, leading to a fatal condition called pulmonary embolism (Figure 1).

DVT affects hundreds of thousands of Americans each year and is a huge economic burden. The main causes of DVT, as described in Virchow’s Triad, are a genetic predisposition, blood vessel injury, and immobility (Figure 2). 

Whereas genetic predisposition and blood vessel injury are not under our control, immobility is a preventable risk factor. This is the basis of my invention. Immobility associated with prolonged blood rest, sedentary desk jobs, and long air/space travel is a major risk for DVT [7]. Athletes are at higher risk for DVT because of their low heart rate, and 85% of the air-travel DVT victims are athletes [8]. Moderate foot exercise greatly improves blood flow compared to sitting still [9]. My objective was to design and test (in human subjects) a simple, portable, pedal that would prevent the risk of DVT. Unlike currently available DVT prevention products that use compression to improve muscle activity (and therefore blood flow), my device would use resistance to improve blood flow. I hypothesize that use of my DVT Prevention Pedal will significantly improve muscle activity in the leg. 

Research

Leg exercises greatly improve blood flow during prolonged immobility, which reinforces the importance of leg movement to prevent DVT [9]. There are a limited number of DVT Prevention products that are currently available to decrease the risk of DVT. The most common product available is elastic stockings which use compression to increase blood flow. However, in addition to being uncomfortable, expensive, and lacking data of their long-term effects, there is insufficient evidence to support the claim that using elastic compression stockings effectively improves muscle activity [6]. 

Although resistance training improves blood flow, the challenge to many people who are immobile for long periods of time (i.e. air travel, road trips, desk jobs), is that they do not have space or are otherwise unable to do these movements. The DVT Prevention Pedal eliminates the need for space to move and simply allows the user to strap it on their foot and pedal away. I validated my device in human subjects while using the pedal by measuring muscle activity, using electromyography.

Method / Testing and Redesign

Materials:

  • Wooden slabs, steel rod, Newton meter (Laramie Junior High School, Industrial Arts and Science Department)
  • Hinges and rubber grips (Ace Hardware, Laramie, WY)
  • Torsion springs (www.granger.com)
  • Delsys Myomonitor EMG System (Boston, MA), Department of Kinesiology and Health, University of Wyoming, Laramie, WY
  • MyoWare Muscle Sensor, Muscle Sensor Surface EMG Electrodes Covidien (Pack of 6), Premium Male/Male Jumper Wire, Silicone Cover Stranded-Core Wire, USB Isolator - 100mA, USB cable, USB A/Micro Cable (www.adafruit.com)  
  • Velcro, Adjustable 30W 110V soldering iron (Walmart, Laramie, WY)

Methods: 

  • Design of the DVT Prevention Pedal: The pedal consists of two 6.5x4.0 inch slabs of wood, which are connected by two hinges. On the sides, there are two torsion springs that are held in place by a metal rod. A Velcro strap was attached to secure the foot and rubber grips at the bottom keep the pedal in place during use (Figure 3).

  • Resistance measurements: A Newton meter was used to measure the resistance offered by the spring. A resistance of 58 newtons/square inch was chosen based on the recommended degree of compression. 
  • DVT Prevention Pedal 2.0: A second pedal was designed with a set of springs with a higher resistance (Figure 4).

  • Human testing of the device: The human study was approved by the Institution Review Board of Wyoming ISEF and this study was done at the Department of Kinesiology and Health at the University of Wyoming under the supervision of Dr. Boyi Dai (Professor of Kinesiology and Health at the University of Wyoming). Three human subjects were used for the study. Informed consent was obtained from the subjects before testing. The Delsys Myomonitor EMG (electromyography) System can evaluate the muscle function in a non-invasive manner in real-time. For the EMG recordings, the sensors were placed using adhesive on the gastrocnemius muscle. An additional sensor was placed on the bone of the wrist (this is used as a reference point for non-muscle data). The subjects pedaled to the rate of a metronome (60 beats/min). Additional recordings were done with the subject walking and during isometric extension of the muscle (using leg muscles to maximum capacity by pushing upward without moving the knee) in the absence of the device [10]. The walking and isometric data were used to compare the pedal data (Figure 5). 

  • DVT Prevention Pedal 3.0I also designed a portable EMG sensor as an add-on feature, which can be connected to a mobile device, for the user to be able to monitor their muscle activity produced while using the pedal. I purchased a Myoware muscle sensor that uses EMG to sense the electrical activity of muscles. The electrodes go on the muscle and it gives an analog output signal. A microcontroller converts the analog output to a digital output, which can be read on the mobile device. The device also has a USB separator, to prevent any mishaps when it is in contact with the skin (Figure 6).  

 

Results

Baseline EMG recordings were done with the subject walking and during isometric extension of the muscle (using leg muscles to maximum capacity by pushing upward without moving the knee) in the absence of the pedals. The walking and isometric data were used as controls. The graph summarizing the results shows the average medial and lateral gastrocnemius muscle activity for each subject normalized to the subject’s maximum muscle activity during isometric contraction is summarized in Figure 7.

As shown in the figure, subject 1 achieved approximately 40% of the muscle contraction while using the pedal as compared to the muscle contraction during walking. subject 1 also achieved close to maximal contraction during the process of walking. For subjects 1 and 3, the muscle activity during pedaling exercise was higher. For subject 2, the muscle contraction during high-resistance pedal was equivalent to that of walking. However, for this subject walking resulted in only half of the maximum muscle contraction, indicating that this subject uses less muscle activity while walking. For subject 3, the muscle contraction during high resistance pedal averaged 0.1 (in contrast to the other two subjects which averaged about 0.5), suggesting that the subject is much stronger and pedaling takes much less effort. This was supported by the fact that subject 3 had the maximal isometric muscle contraction. This subject was stronger than subjects 1 and 2, which is why using the pedal did not increase muscle contraction substantially, which suggests that such subjects may need a higher resistance pedal. Using device 3.0, I was able to record muscle activity, a representative tracing of which is illustrated in Figure 8.

Conclusion

In summary, the results show that I was successful in creating a device that would increase muscle activity. I have also successfully demonstrated the proof of principle for creating a simple device that can measure muscle activity on the go. Using this device could increase blood flow in the leg, thereby reducing the risk of DVT.

Through this project, I have come to three major conclusions. 

1. Human studies show that the muscle activity when using the DVT Prevention Pedal is comparable to that observed during walking in an average adult (seen in subject 2). 

2. With a muscular/strong subject, the muscle activity when using the pedal is modest. A higher resistance is needed for stronger subjects. This can be achieved by having an adjustable resistance (springs) pedal.

3. This simple, portable, DVT Prevention Pedal can be used at work, during travel, or when relaxing to improve activity in the leg muscle and prevent the risk of DVT.

A major limitation of this pilot study was that it was done with only three subjects. An additional shortcoming of this study was that I was unable to measure blood flow. In the future, I would like to test my devices in a larger group of subjects using my portable EMG device and pedal with varying resistance. I would like to also take measurements of blood flow using Doppler ultrasound. Furthermore, I would like to patent an updated design of the pedal with adjustable resistances to accommodate customer needs.

About me

My name is Arundathi Nair and I am a Junior at Laramie High School in Laramie, Wyoming. I first got excited about science when my second-grade teacher required us to make a science fair project. When my dad and I would go to the gym, I always wondered why it was that when we were running for the same amount of time at the same speed, that he burned more calories than I did. I pursued this question for my project and have loved science ever since. The 3M Young Scientist Challenge sparked my interest in innovation and filmmaking. I have been able to present at several national meetings including the International Science and Engineering Fair, the National Junior Science and Humanities Symposium, the Army Science and Technology Showcase and Symposium, and the International Career Development Conference. Through these opportunities, I have been able to meet many amazing young scientists and learn about science and how it can change lives. In addition to science, my other major interest is journalism and making documentaries. My documentaries have won 1st and 2nd places in the National C-SPAN StudentCam Video Documentary Competition. When I go to college, I want to go into the biomedical engineering field because of my love for invention and discovery. My favorite scientists are James Watson and Francis Crick because of their discovery of DNA, which changed our world. The prizes that the Google Science Fair offers would help me pay for college and expand my experiences.

Health & Safety

I obtained an IRB for the human pilot study conducted in this project. Dr. Boyi Dai, Professor of Kinesiology and Health at the University of Wyoming, supervised the pilot study. His contact information is bdai@uwyo.edu.The data is presented in a de-identified format. There were no health/safety hazards involved in this project.

Bibliography, references, and acknowledgements

References 

1. Beckman MG, Venous Thromboembolism A Public Health Concern. American Journal of Prev entive Medicine 38S495-501, 2010.

2. Centers for Disease Control and Prevention, http://www.cdc.gov/ncbddd/dvt/data.html

3. Fowler P, Danger! Deep Vein Thrombosis Deep Vein Thrombosis Health Center, WebMD Feature, http://www.webmd.com/dvt/features/deep-vein-thrombosis, Dec 20, 2015.

4. Gross S, Incidence based cost-estimates require population-based incidence data. Thromb Haemost 107:192–193, 2012.

5. Greets WH et. al., Prevention of Venous Thromboembolism: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 133: 381-453, 2008.

6. Kolbach D, Sandbrink M, Neumann H, Prins M. Compression therapy for treating stage I and II (Widmer) post-thrombotic syndrome. Cochrane Database Syst Rev 4: CD004177, 2003. 

7. Healy B, et. al., Prolonged work- and computer-related seated immobility and risk of venous thromboembolism. Journal of Royal Society of Medicine 103: 447-54, 2010.

8. Parker B, Deep Vein Thrombosis in Athletes: Risks of Racing and Resting. Journal of the American Medical Athletic Association 23: 8-11, 2010.

9. Hetos K et. al., Effect of leg exercises on popliteal venous blood flow during prolonged immobility of seated subjects: implications for prevention of travel-related deep vein thrombosis. Journal of Thrombosis and Hemostasis 5: 1890-1895, 2007.

10. Fisher H et. al., The Relationship between Force Production during Isometric Squats and Knee Flexion Angles during Landing. Journal of Strength Conditioning Research 6: 1670-9, 2015. 

Acknowledgments

I did not have a formal mentor for this project. I conceived this project on my own, however, the following individuals helped me throughout the project.

Dr. Boyi Dai, PhD. Assistant Professor, Kinesiology and Health, University of Wyoming, Laramie, WY (helped with muscle activity measurements). I conducted the pilot study in Dr. Dai’s lab and used his equipment.

Dr. Paul Dellenback, PhD., Professor, Department of Mechanical Engineering, University of Wyoming (discussed torque and torsion springs).

Mr. Doug Brenneman, Industrial Arts Teacher, Laramie Junior High School (helped with building the device).

Mr. Vinay Bharadwaj, Graduate Student, Electrical Engineering Department (helped with circuitry for the homemade electromyograph device).

Human volunteers for their participation in the study.