Some diabetic patients receive no warning before they pass out from low blood sugar. A modern sweat meter could alert patients in time. Biathletes and ME patients might also benefit from the sweat meter.
By Yngve Vogt, research magazine Apollon, University of Oslo, Norway
25,000 Norwegians have type 1 diabetes. 175,000 have type 2 diabetes. Add to this the large number of people who are unaware that they are diabetic. When the concentration of sugar in the blood drops, most patients have a hypo (a hypoglycaemic attack). Symptoms may include palpitations, sweating, a tingling feeling in your face, altered sensory experiences and intense hunger.
After many years with diabetes some patients lose warning symptoms of low blood sugar. It's a very scary condition because they can then lose consciousness or die. Today there are no good instruments that can measure this without the patient pricking themselves with a needle.
In a few years diabetes patients may get help with avoiding dangerously low blood sugar.
It is known that diabetic patients change their sweat pattern when their blood sugar levels are too low. A sweat meter developed at the University of Oslo and the National Hospital can send a discreet alert - via a mobile phone - before a patient suffers an attack due to low blood sugar.
"The advantage of the sweat meter is that the patient doesn't have to prick themselves. All you need to do is paste an electrode on your skin," says Professor Ørjan G. Martinsen, Department of Physics at the University of Oslo to the research-magazine Apollon at University of Oslo, Norway.
"We envisage that the device will be able to measure sweat activity continuously, providing an indication of whether the patient is about to experience low blood sugar. It can communicate directly or via a smartphone. The warning system will then not be very bothersome for the patient," says Christian Tronstad, a medical technology researcher at Oslo University Hospital, the National Hospital.
Medical interest. Diabetes expert Professor Trond Geir Jenssen at the National Hospital told Apollon that he has great faith that the sweat meter will be helpful to diabetics.
With support from the Norwegian Diabetes Association, the researchers will now carry out sweat measurements of diabetic patients when their blood sugar level dips.
"In the study we will compare the continuous measurements of sweat activity and blood sugar in patients to see if we can get a good enough warning of a low sugar level in the blood," says Tronstad.
Professor of Medicine Kåre Birkeland, head of the medical council of the Diabetes Association, says the sweat meter is exciting.
"It can be developed into a practical, usable device that can help those who have a hypo when their blood sugar gets too low. The patient can then take the necessary precautions," says Birkeland.
He noted that more studies have to be done before the sweat meter can be used.
Electrical resistance in tissues. Professor Martinsen's research group leads the world in knowledge of the electrical properties of the skin. Together with Sverre Grimnes, professor emeritus of medical technology, he has, over the last 20 years, researched bioimpedance, i.e. electrical resistance of biological tissues. The research group in Oslo has therefore called itself the Bioimpedance Group.
They have started the world's only scientific journal on bioimpedance. Martinsen is also president of the International Society for Electrical Bio-Impedance.
Unnoticable palm sweat. The sweat meter was originally designed to diagnose hyperhidrosis, a nasty disease that causes sufferers to sweat excessively. Researchers are currently using the sweat meter to examine diabetes patients at the National Hospital and Akershus University Hospital (Ahus).
Sweating has two causes. The best known is thermal sweat. When it's hot, the body reacts by secreting sweat on the surface of the skin. The perspiration needs energy to evaporate. This cools the skin down.
The second type of sweat is emotionally controlled and occurs primarily in the palm. The palm has more than 250 sweat ducts per square centimeter. This is the highest density of sweat glands in the body. In comparison, the forearm doesn't have more than 100 sweat ducts per square centimeter.
"Although emotionally controlled sweat can be unnoticeable, it can have a great impact on measurements, even when you're only calculating a few difficult math problems in your head," says Martinsen.
The sweat meter sends a small electrical current through the outer part of the skin, into the sweat glands and out onto the surface again. This layer of skin, which consists of dead horn cells, is as thin as the plastic film you use to wrap food, only 10 to 15 micrometers thick. Horn cells are poor conductors of electricity. On the other hand, sweat is a good conductor of electricity. Sweat is made up of saltwater. As is known, saltwater conducts electricity. The conductivity of the skin increases, therefore, when the sweat pores are filled with sweat.
Over the past year, several medical research institutes have expressed an interest in the sweat meter.
Athletes and stress. The sweat meter can be used to see how upset or excited you are.
"Imagine a biathlete! He has to ski extremely fast and then has to suddenly calm down to shoot at the target. With the sweat meter, he can practice relaxing as quickly as possible. Perhaps it's wise to count to ten, wait a few seconds or even think about Christmas dinner. The point is that the athlete gets feedback on what works," says Martinsen.
Chronic Fatigue Syndrome. Vegard Bruun Wyller, chief physician at the Paediatric Cardiology Department at Oslo University Hospital and associate professor at the University of Oslo, will test the sweat meter on children with chronic fatigue syndrome (ME).
Even when ME patients rest quietly and should be relaxed, their bodies behave as though they are persistently stressed. Many complain of sweating.
"We want to use the sweat meter to see if people with ME have increased sweat secretion. If this can be verified, it may be appropriate to proceed with more sophisticated, experimental studies," says Bruun Wyller.
Night sweats. Some people sweat profusely at night. Oslo researchers have also started a collaboration with the world's leading experts on night sweating at Lynn Health Science Institute and the University of Oklahoma, to use the sweat meter to monitor night sweating.
Technology. Although the sweat meter looks simple, it is packed with advanced technology.
A current passes through the electrodes. The sweat meter requires at least three electrodes.
"With two electrodes, it's not possible to separate the signals from the various electrodes from each other. By using multiple measuring points, we get a control system where we can keep track of the contributions of each electrode," says Tronstad.
They have developed special electrodes that do not affect the measurements.
"This ensures optimal focus on the outer part of the skin where sweating occurs."
The electrodes in the old models, which University of Oslo researchers developed a few years ago, created artificial signals. The measurements were not that reliable.
While the old, familiar lie detectors use direct current, the new sweat meter uses alternating current. With DC the current direction is constant. With AC the direction of the current changes all the time.
"DC has a long history and is used in conservative research communities. Some scientists in psychological communities cling to this method. We were met with scepticism, but were eventually accepted."
The natural electrical power of the body, such as muscle and nerve cells, is equal to 0.15 V, one-hundredth of an ordinary 1.5 V battery.
"This current is direct current. The problem is that it's not possible to measure direct current with direct current, since it isn't possible to separate these two direct currents from each other. Moreover, AC doesn't affect biological material as much as DC."
New electrical component. The research group has also begun using a completely new component of electric circuits.
In traditional physics electric circuits consist of three components: resistor, capacitor and inductor. Resistance is defined in the famous Ohm's law as voltage equals resistance times current.
"You can compare these concepts with a water hose: The voltage is the water pressure. Resistance is how much you squeeze the hose. The current is the water that forces its way through the hose."
In recent years, physicists have discovered a fourth basic component of electric circuits. It is called a memristor.
A memristor is resistance with memory. This means that resistance is dependent on the amount of charges that have already come through.
"This may sound commonplace, but the memristor was not theoretically described until 1971."
Not until 2009 did scientists manage to make a nanomemristor.
"A memristor is perfect for creating electrical models of the skin. We're the first scientists in the world to have adopted this theory in bioimpedance. It enables us to create even better methods of measuring electricity in the skin and thus better models of sweat ducts. Memristors can also be used to improve models of nerve signals, and have actual consequences for all fields that deal with electricity," explains Ørjan Martinsen.
The memristor research of the Oslo physicists was recently published in the prestigious journal New Scientist.
Checking acupuncture. Knowledge of bioimpedance is also important for understanding acupuncture. In traditional Chinese medicine our bodies have meridians (median lines) or pathways. They believe that life energy flows along these paths and that diseases are caused when the flow of energy is disrupted.
"They therefore dissolve the obstacles by inserting acupuncture needles into these meridians. Many believe that these meridians have special electrical properties. The problem is that many scientific papers in this field do not have a high enough standard. We have set up guidelines for how the studies should be done, and want get to the bottom of whether the meridians exist and whether acupuncture points have special electrical properties," says Martinsen.
In collaboration with the Massachusetts Institute of Technology, University of California and Harvard University, the Norwegian scientists will now measure whether the skin has line patterns or acupuncture points with special electrical properties.