Freitas and his group tested volunteers to measure the grip force exerted by diabetics with and without a diagnosis of neuropathy, as well as healthy subjects, and developed a methodology that can be used to produce equipment for use in clinical practice. In future, the innovation should help physicians diagnose the disorder quickly and easily not long after the onset of initial symptoms of neuropathy in diabetics.
The analysis focused on grip force used to hold and manipulate objects, and on relative safety margin, i.e. grip force normalized by the coefficient of friction between skin in contact with the object and surface of the manipulated material. The central nervous system "calculates" the amount of force needed to hold an object, learning to do so better over time. "Every object has a contact surface with which our fingers create friction when we hold it. The smoother the surface, the more grip force needed to hold it. If it is rough, we can use less grip force thanks to friction," Freitas explained.
Considering grip force and safety margin, people with neurological disorders such as multiple sclerosis and Parkinson’s tend to use more force to grip objects than healthy people. The force needed to manipulate an object is moderately greater than the minimum force needed to hold it in the desired position. "In the case of people with neurological alterations, our hypothesis is that they grip objects more strongly as a conservative strategy," Freitas said. "The nervous system detects a neurological deficiency and sends a command for the hand to use more force as it grips the objects. This process is entirely unconscious, of course."
The test results showed that healthy volunteers used between 100% and 120% of the minimum force required to hold an object, whereas the force used by participants with neurological alterations was two and a half times to three times greater.
Freitas and his team then investigated the performance of diabetics, who typically suffer from neuropathy as the disease worsens. "There was no prior research on diabetics involving the type of experiment we used in our study," he said.
The hypothesis was that diabetics would grip objects more tightly, as is the case with people who suffer from carpal tunnel syndrome, multiple sclerosis and Parkinson's. "However, what we found was the opposite: diabetics used half as much force to hold an object as controls in the simplest task, which was the static test, in which the subject merely has to hold an object without manipulating it," Freitas said.
Three types of test were conducted with 36 volunteers, including 24 diabetics divided into two groups: 12 who had developed neuropathy, and 12 who had neither been diagnosed with neuropathy nor displayed clinical signs of the disorder. The other 12 participants were healthy and formed the control group. Before testing began, the researchers measured each participant’s skin sensitivity, since the sense of touch is a key factor in conveying to the central nervous system the information required by the brain to calculate the force needed to hold and manipulate objects.
Volunteers were each asked to perform three tasks using the same type of object instrumented to measure force. In the static holding test, they had to hold the object with their dominant hand as if they were holding a glass of water. A beep sounded after ten seconds, and they were to unclasp their fingers slowly so as to release the object, while a researcher measured the friction between the fingers and the object. The second task consisted of picking up an object from a table, lifting it about 5 cm, holding it for 10 seconds, and putting it back on the table. In the third task, termed oscillation, the volunteers had to grasp the object, hold it in front of their navel, and move it about 20 cm up and down for 15 seconds.
In the second and third tasks, the results for diabetics and diabetics with neuropathy were similar to those for controls. The surprise came in the simplest task of all, which was static holding, as diabetics and diabetics with neuropathy used half the force applied by the controls.
The explanation is not exactly a loss of sensitivity in the fingers of diabetics, the researchers explained, but deficient tactile information sent from their fingertips to the central nervous system. There is not enough information of high quality for the brain to make the requisite calculations and the hand to use the right amount of force. "In addition, there are studies showing that certain areas of the spinal cord and cortex that receive and process this sensory information are smaller in diabetics than in healthy people," Freitas said.
The study suggests diabetes does not only affect the periphery of the body, causing loss of sensitivity in the toes and fingers, for example, but also affects the central nervous system. "This happens early in diabetes. People tend to think these complications happen only after a certain age or when a person has had diabetes for some time, but actually patients have the problem before neuropathy is diagnosed," Freitas said.
MEDICA-tradefair.com; Source: Fundação de Amparo à Pesquisa do Estado de São Paulo
