The other limit of continuous health surveillance can be superficial.
Biomedical engineers at the University of Cincinnati say interstitial fluid, a watery fluid found between and around cells, tissues or organs in the body, could be an excellent tool for early disease detection or long-term health monitoring.
In an article published in the journal Nature Biomedical Engineering , they describe the potential benefits and technological challenges of using interstitial fluid.
"The reason we consider it a valuable diagnostic fluid is because of its constant availability. You can't measure blood all the time," says study co-author Mark Friedel, a graduate student at the University of California.
"Can you imagine spending all day with a needle in your vein? So we need other tools."
Researchers are looking for alternatives to monitor human health and well-being. Sweat is a good way to measure things like stress or anxiety because it contains hormones like cortisol. But the body is stingy with other chemicals that aren't as easily eliminated through sweat, Friedel said.
"Sweat glands are big filters that keep everything out," he said. "That's why more than half of the things we want to track don't have access to sweat."
Blood is the gold standard for health monitoring. But humans also have liters of interstitial fluid that makes up up to 15% of their body weight.
"The main characteristic of blood that makes it so useful is that we understand blood very well," Friedel said. "If you have something in your blood, we know what's going to happen to your heart or your liver," he said.
The researchers said the interstitial fluid contains many of the same chemicals as blood in the same proportions, offering a potential alternative to expensive and time-consuming lab work.
The study describes several methods for collecting interstitial fluid samples, from skin aspiration to microdialysis.
"As biomedical engineers, one of our main goals is to help people better manage their health by making diagnostics more accessible," said co-author Ian Thompson of Stanford University.
“A major obstacle to this availability is that most current diagnostic methods rely on blood samples, which can be painful and require trained personnel to perform. Therefore, there is a growing interest in using just subcutaneous interstitial fluid as a diagnostic probe. more accessible and less painful to remove.
At the University of California's College of Engineering and Applied Sciences Laboratory for New Devices, professor Jason Heikenfeld is developing sensors to measure hormones and other chemicals in tissue fluids. They use microneedles less than 1 millimeter long that pierce the skin in a small area.
"If you had a patch, it probably went deeper into the skin than our microneedles," Friedel said. "They're usually painless. Most of the time I don't feel them. The most uncomfortable part is removing the tape that holds the device on."
But even if you don't know it's there, your body does, Friedel said. And this smallest reaction can affect the test results.
“There is a Schrödinger Observer effect with the interstitial fluid. Every time you try to collect and measure it, you're essentially changing the fluid itself," Friedel said. "When you stick a needle in your skin, your body swells, and then the [sample] levels change. For continuous biomonitoring, we want to know what these levels are like when you're not getting poked with a tiny needle.
"That's why it's such a complex fluid that it hasn't been used outside of diabetes monitoring."
However, researchers say interstitial fluid holds promise for health monitoring through wearable technology. This can help doctors monitor the effectiveness of drugs to ensure proper dosing or ensure early diagnosis of a disease by monitoring the immune system.
But Friedel said he still had a lot to learn.
"We are trying to open the box and read the instructions inside to understand what is in the interstitial fluid and the potential of its use," he said.
For more information: Mark Friedel et al., Opportunities and challenges in the diagnostic value of skin interstitial fluid, Nature Biomedical Engineering (2023). DOI: 10.1038/s41551-022-00998-9
Quote from: Get under the skin for better health with the interstitial fluid test (January 20, 2023) Accessed January 28, 2023 at https://medicalxpress.com/news/2023-01-skin-health-interstitial-fluid. html
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