Continuous challenges
PhD researcher Yu Zhang joined this research project at the end of 2023 under the supervision of Yuan Lu, Panos Markopoulos (TU/e ID), and Hanneke van Santen. He set about getting to know his research topic with an extensive literature study.
“It was immediately clear that sodium levels in the blood are a critical factor to be monitored continuously to keep track of one’s fluid balance,” he explains.
“The fluid balance between water and electrolytes (such as sodium) is important to keep the body functioning optimally and to prevent dehydration or its direct opposite: water intoxication. So, the sodium level was the first key parameter I wanted to incorporate in the smart device.”
An alternative to sweat
One of the first things that comes to mind when considering a smartwatch is that it could be suited to measure chemicals on the skin’s surface, such as in sweat. But, for Zhang, this idea was the first big disappointment in the project.
“Unfortunately, the sodium level in your sweat does not have a strong enough correlation with the sodium level in your blood to be effectively used for this group of patients,” Zhang explains.
“The fluid that does bear a strong correlation is the liquid between the cells in your body. This is called the interstitial fluid. To ensure that monitoring is as minimally invasive as possible, we want to measure that fluid just one millimeter below the skin’s surface.”
“I will be looking into new and novel ways of measuring sodium levels in interstitial fluids because I have not encountered a standard method.”