When officers arrive on the scene of “shots fired,” they hope for the best but anticipate the worst. Worst case scenario: the victim has already succumbed to his/her injuries. Second worst-case scenario: the victim is hemorrhaging due to their injuries and needs a hospital—stat.
Since there is no direct way for police, first-responders and physicians to know how much blood a victim has lost, they are often at a disadvantage. A new “wearable” developed by researchers at Georgia Tech seeks to counter that disadvantage by accurately assessing blood loss via seismic vibrations in the chest cavity.
Currently, blood pressure is the commonly used to assess blood loss, but it’s not a perfect measurement. In fact, a person’s blood pressure can remain stable until blood loss reaches a critical level.
"It's very difficult because the vital signs you can measure easily are the ones that the body tries very hard to regulate. Yet you have to make decisions about how much fluid to give an injured person, how to treat them—and when there are multiple people injured—how to triage those with the most critical needs. We don't have a good medical indicator that we can measure noninvasively at an injury or battlefield scene to help make these decisions,” said Omer Inan, professor at Georgia Tech and co-author of the study published in Science Advances.
Based on Inan’s research with colleagues and collaborators, though, there may soon be an alternative. In their study, the researchers used swine animal models to study seismic vibrations from the chest cavity and electrical signals from the heart. They compared these externally measurable indicators with results from catheters, which were set up to take direct measurements of blood volume and pressure.
Utilizing three sensing modalities—electrocardiogram, seismocardiogram and photoplethysmogram—the researchers showed data from the proposed wearable platform matched that of the catheter-based system. Critically, the seismocardiogram, which measures micro-vibrations produced by heart contractions, showed changes in the timing of the heart's activity as blood volume decreased—a measure of a weakening cardiovascular system.
"The most critical lower level feature we found to be important in blood volume status estimation were cardiac timing intervals: how long the heart spends in different phases of its operation," Inan said. "In the case of blood volume depletion, the interval is an important indicator that you could obtain using signals from a wearable device."
Inan and his team hope the knowledge they developed in the laboratory will lead to a field-deployable wearable device backed by smart features and even machine learning algorithms that could generate a numerical score regarding the severity of a patient’s condition.
In future work, the researchers expect to create a prototype device that could take the form of a 10-mm patch. Additional electrical engineering will be needed to filter out background noise likely to be found in real-world trauma situations, and for successful operation when the patient is being transported.
Photo: Researchers have shown that they can accurately assess blood loss by measuring seismic vibrations in the chest cavity and by detecting changes in the timing of heartbeats. Credit: Georgia Tech