Graduate engineering students at MIT who are working with supervising doctors made presentations to a Forum audience at Simches Research Center at Massachusetts General Hospital on March 11 for the second time in two weeks. Three teams discussed their proposed solutions to medical problems that doctors have posed, with Rajiv Gupta, MD, a radiologist at MGH, serving as moderator. The teams have just one semester to develop a prototype that addresses the doctor’s real-life challenge.

One team is developing an “accurate non-invasive electronic monitor for human body hydration.” It is headed by Lynne Levitsky, MD, associate professor of pediatrics at Harvard Medical School, and with MGH. Team members included Al-Thaddeus Avestruz, Michael Rinehart, Anthony Sagneri and Alexander Hayman.

There is a continued need for a non-invasive method to accurately measure the level of hydration in humans. In its development of a prototype, this team uses low-power RF energy from 100 kHz to 10 MHz to measure the loss tangent of the frontalis muscle (in the forehead). The group pays particular attention to the skin-electrode interface and employs a four-electrode geometry to measure the localized complex impedance. From this they can derive the loss tangent, which is potentially a large improvement over other techniques which use full body impedance.

Another team investigated a “catheter-based device for intra-cardiac mitral valve chord manipulation.” This project focused on the design and implementation of a catheter-guided device that has the potential to help physicians mitigate the effects of mitral valve regurgitation. The purpose of their device is to provide physicians with a tool that may be controlled externally and is capable of manipulating the charade tendinae within the heart. The proposed device is important because many patients do not have the level of health to survive open-heart surgery. The team was led by Robert Levine, MD, professor of medicine at Harvard Medical School and also with MGH. Team members included Will Bosworth, Ari Mazumdar, Miguel Saez and Alex Slocum Jr.

The third team focused on a “transfascial hernia fixation device.” Hernias represent a common surgical problem, and laparoscopic repair is becoming increasingly more common. In this approach, small incisions are made in the abdominal wall, laparoscopic ports are placed and the hernia defect repaired using a piece of prosthetic mesh. This team proposed a novel way to affix mesh to the abdominal wall during the surgery. The premise is that this device will be easier to use, thus reducing operation room time and patient costs. It could result in less post-operative pain for the patient. The team was led by Ali Tavakkolizedeh, MD, instructor of surgery at Harvard Medical School and also with Brigham and Women’s Hospital. Team members included Megan Roberts, Michael Eilenberg, Jessica Galie, and supervisors Rajiv Gupta and Martin Culpepper, PhD.

A need exists to accurately monitor hydration in human beings.  Water regulation in humans involves osmoreceptors in the brain as well as baroreceptors in the large blood vessels.  These receptors send signals to the brain to control the release of vasopressin, also known as antidiuretic hormone (ADH), from the posterior pituitary.  Decreased fluid intake results in increased vasopressin and decreased urine volume.  Increased fluid intake results in decreased vasopressin and increased urine volume.  These regulatory mechanisms can fail in disease states such as diabetes insipidus where vasopressin is not produced or in SIADH (syndrome of inappropriate antidiuretic hormone) where ADH is produced to excess.  Other disorders of water regulation occur when there is inadequate water intake due to inadequate thirst mechanisms or the inability to drink independently, resulting in the risk of hyponatremia or hypernatremia with over-hydration or under-hydration.  Water regulation problems may be found in the elderly and infirm, infants, patients receiving intravenous fluids, patients receiving nutrition via gastrostomy or jejunostomy tubes, and athletes (especially long-distance runners exerting themselves).   

Graduate students at MIT have developed a non-invasive method for electronic monitoring of hydration, using radio frequency energy from 100kHz to 10 MHz to measure the loss tangent of the frontalis muscle, which is located in the forehead.  The frontalis muscle was chosen because of its large surface area and its high level of vascularization.  The loss tangent, a function of electrical conductivity and permittivity, reflects the muscle’s osmolality and thus its hydration status.  It is independent of sensor electrode geometry.  Using a four-electrode configuration, the students’ device measured the impedance of the frontalis muscle and calculated the loss tangent.  The loss tangent of the frontalis muscle is an indicator of the muscle’s hydration level, and measuring the loss tangent provides a method for non-invasively monitoring human hydration.                

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