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CoE for Limb Loss Prevention and Prosthetic Engineering

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Diabetic Thermoregulation and Perception of Comfort

PI: Glenn K. Klute, Ph.D.
Agency: Department of Veteran Affairs

Objective: Diabetes is the leading cause of lower limb amputation. Diabetic limb loss is often associated with decreased circulation and loss of sensation because infected ulcerations go unnoticed or have trouble healing. Diabetes has also been connected to impaired thermoregulations, which is highly dependent on sensation, nerve function and circulation. Temperature nerves on the skin are responsible for communicating sensation, warm or cold, and for triggering a vascular response. Deviation above or below a thermally comfortable zone will make one perceive being warm or cold. The behavioral response to avoid heat stress is to change one’s environment or to compensate (for instance drinking a hot or cold beverage). When a warm signal is perceived, the blood vessels near the skin dilate to convect heat away from the core of the body. When the perception is cold, the blood vessels constrict to reduce blood to the skin and prevent heat loss. Degeneration of this nerve function or decreased blood flow to the surface may be responsible for irregular thermoregulatory response. Our objective is to understand if and how the thermoregulatory response and perception of warm and cool have been altered in the legs of diabetics. Our understanding of the nature of thermoregulation in diabetics will help in the design of a prosthetic socket, which maintains a comfortable temperature. It may also become evident that there is a need to assist diabetics with thermoregulation.

Research Design: The goal of the proposed project is to understand if and how thermal perception and thermoregulation is altered in the legs of diabetics. We will conduct an experiment to determine the point at which an individual perceives a warm sensation and a cold sensation. We will also determine at what temperature there is a vascular response. These tests will allow us to determine how coordinated thermal perception and vascular reactivity is and the degree the thermoregulatory response is altered in diabetics.

Methodology: The specific aims include a) determining the temperature when an individual with diabetes perceives warm and cold; and b) determining the temperature at which blood vessels constrict or dilate as a thermoregulatory response. Thermal perception will be determined by placing a Peltier-controlled thermode of the subject’s leg and slowly ramping the temperature up or down until the temperature is perceived. Synchronously, a Laser Doppler Flowmeter will measure the blood flux at the point directly in the center of the thermode-skin interface.

Warm and cold thermal perception will be tested while the individual is sitting and walking. The thermode will start at four separate baseline temperatures while seated and two while walking.

Findings: Results from the tests will give insight into if thermal perception or vascular reactivity is altered in amputees and diabetics. Results will also test whether thermal perception is activity dependent and whether initial temperature matters. This lab has found that simply donning the prosthesis results in a slight skin temperature increase. It will be important to know how individuals adapt to the elevated temperature and how that alters their perception. Information about the thermoregulatory response and thermal perception of diabetics will be used to design a thermally comfortable socket. The information will also be used to design a device, which assists with thermoregulation to prevent heat stresses on the body.

The water block helps to cool off the Peltier chip

The water block (left) on helps to cool off the Peltier chip (center) which controls the temperature of the thermode. The copper interface will slowly heat up or cool off as the Peltier chip changes temperature. The laser Doppler flowmeter in the center of the copper piece will measure the vascular response to temperature.

Milestones: The thermode has been designed, developed, and tested. Institutional Review Board approval is in progress. This project is currently supporting one graduate student.