Peripheral Neuropathy Device

Peripheral Neuropathy Device (PND)

Spring 2013 MAE 156B SPONSORED PROJECT

UNIVERSITY OF CALIFORNIA, SAN DIEGO

Sponsor: Dr. Heather Hofflich

Figure 1.  Peripheral Neuropathy Device

(click on any picture to enlarge)

Background:

Every year, millions of people become affected by diabetes.  Roughly 26 million people currently suffer from Type 1 or Type 2 diabetes, which accounts for 8.3% of the American population.

One of the most noticeable and concerning symptoms of diabetes, that is very dangerous, is the sensation loss in limbs that develops over time.  As a result, they exert a lot of pressure at one spot on the bottom of the foot when walking, thus building up calluses at that spot without causing discomfort.  The pressure on the callus becomes so high that eventually it causes breakdown of tissues and ulcers appear.  These sores and ulcers are exceedingly difficult to treat and heal slowly on their own; they must be treated with high care and an antibiotic regime.  Sometimes this treatment is not sufficient and leads to amputation.

Most of the trauma that arises as a result of diabetes can be prevented. The goal of the Peripheral Neuropathy Device is to measure the loss of sensation in patient’s feet so education and treatment can be easier to advocate.

             (a)                                (b)

Figure 2.  (a) A foot with an ulcer.  (b) An image of normal skin compared to an ulceration in the skin.  

Photo courtesy of American Academy of Family Physicians (AAFP)

Existing Solutions:

Figure 3. The current test, the Monofilament Test

The current test, the monofilament test, is a stiff nylon thread that buckles when a load of 10 grams or more is applied.  This quantity represents a baseline level of sensation that can be considered 'the line' between having neuropathy and normal sensation.  When it is placed against the foot with slight pressure and buckles, a person with normal sensation should feel the sensation (which is roughly 10 grams or less).  If it's pressure is not felt in at least four out of the ten predefined areas, then it is reasonable to assume that diabetic neuropathy is present, and extra precautions need to be practiced to protect the foot from further sensation loss.  

The monofilament test only results in a "yes" or "no" ("+" or "-") response when doctors perform the test.  This is considered a very crude and subjective test for several reasons.  If a patient responds with a hesitant or unsure answer and cannot confidently say he or she feels sensation, the test for that point receives a "no" result, which can skew the overall quality of the analysis.  There is no way to determine if sensation is better or worse than 10 grams because the buckling only occurs for one applied force.  Monofilaments expire one year after fabrication, which contributes to unnecessary cost and waste for the products that are not used in that time frame.  Since doctors have the potential of disposing thousands of these monofilaments a year, the cost can add up to thousands of dollars in a short amount of time. 

There are more sensitive tests, such as the nerve conduction study, but are very expensive and cannot be done economically throughout year.  It is likely that insurance policies will not cover these tests because their cost can be over $1,500.

The goal of the project is to develop a device that quantifies sensation loss in diabetic patients' feet in order to better diagnose, regulate, and show prognosis.  Ulcers and amputations are 100% preventable with proper care, and tracking the sensation loss will give the opportunity to prevent many unnecessary surgeries.  The device will further develop a standard which can be widely used for diabetes control and prevention.

Statement of Requirements:

The Peripheral Neuropathy Device is required to provide consistent and accurate information in a short period of time.  The following are the device specifications required:

• Measure applied force numerically with a resolution of 1 gram

• Provide measurements for a force application range of 0 to 75 grams

  • Resolution will be used to determine the numerical difference between loads

• Be handheld

• Deliver numerical information via display screen

• Have a patient button to momentarily freeze the reading when sensation is felt

• Be reusable and reliable

• Be easily cleaned and sterile

• Be easily taken apart

  • For cleaning or access to inner mechanisms

This project has a budget of $1500 and a time frame of three months.

New Solution:

The new solution to peripheral neuropathy is the Peripheral Neuropathy Device (PND).  Below is a high-definition demonstration in a medical setting.

Figure 4.  Video of Peripheral Neuropathy Device Testing

The device consists of six major components:

1. 780-gram binocular load cell

2. 1095 spring steel cantilever spring

3. 0.125-inch diameter stainless steel rod

4. Arduino Micro

5. Texas Instruments INA114-AP instrumental amplifier

6. Monochrome 0.96" OLED graphic display

Combining these six components together gives the device a nonaggressive, iron-like shape that feels comfortable in the hand with easy usability.  Fitted with curves and smooth edges, gives the device a sleek and appealing look to the user.  To steer away from any type of correlation between an image of weapon or associated pain, the device is white to fit in with the motif of other medical products widely used products in medical offices.

The PND has a Red-Green-Blue (RGB) LED that provides information about the data that is being received by constantly emitting green for a range of 0 to 5 grams, a constant yellow for 6 to 10 grams, a constant red for 11 to 20 grams, and flashing red for values of 21 grams or larger.  Once the patient by presses their designated "freeze" button, the LED becomes blue for 3 seconds and then resets the system to be ready to test the next point.

The PND has gone through preliminary tests and has proven to be more quantitative than the monofilament test.  The data collected suggests the device performs better than the monofilament test because instead of yielding a "yes" or "no" result, the user receives a number that can be measured on a scale to determine the severity of neuropathy.  Seen by the data, the locations on the foot where the 10 gram monofilament was felt, the device recorded a force lower than 10 grams.  Also, when the 10 gram monofilament test was not felt on the foot, the device recorded forces greater than 10 grams.  

Figures 5a and 5b (below) show the data collected through one preliminary test on a diabetic patient.  There were 12 tests conducted on this patient, one was the monofilament test and the remaining 11 were the testing of the device.  A quick look at the graph, one can notice that there are red and green dots representing if the patient did (green) or did not (red) feel the monofilament test.  The other dots on the graph represent the average amount of force applied per location.  One can see that when the patient did not feel the monofilament, the average force applied was above 10 grams.  Also, note that when the patient did feel the monofilament, the average force was below 10 grams.  These results assure that the device is working properly.

(a)                                                                                                                                                                           (b)

Figure 5a and 5b. Average Force Applied per Location on the Foot. 

Impact on Society:

Diabetes, whichever the type, affects a large population on the scale of millions.  The harsh reality is that far more people suffer from diabetes with sores, ulcers, and limb loss in addition to other complications which can be managed, maintained and even reversed.  The Peripheral Neuropathy Device will allow for quantification of the loss of sensation in the diabetic’s feet, which will lead to prevention of ulcers and amputation.  An diagram of an ulcer can be seen in the “Background” section of the website. If the ulcer were to go undetected, or untreated, then it would gradually grow to engulf the entire foot.  Once the ulcer reaches this level of severity, amputation is the only means in containing the spread of the ulcer.  The Peripheral Neuropathy Device will greatly help notice the signs of potential ulcers and sores to potentially help the doctor aid in preventing amputation by detecting loss of sensation in the early stages.  This will positively impact society due to improved monitoring of diabetes which results in the reduction in amputations and overall general health and wellness because doctors will feel more confident in their testing.  With a better understanding and quantification, the doctor can tell the patient if their neuropathy is improving or worsening, an invaluable tool to advocate treatment.  It is currently unknown how often the monofilament test is performed due to its inconsistency, so providing doctors with a reliable tool will increase the likeliness of performing the test, impacting the overall understanding and prognosis of the disease. 

The Peripheral Neuropathy Device:

Below is an isometric CAD model of the latest PND iteration. Figure 6 shows the aesthetic presentation and Figure 7 demonstrates the inner workings of the system.

Figure 6.  Device with annotations

Figure 7.  Internal device with annotations