26 Sep 2023
WUSTL wearable optical sensor tackles a leading cause of maternal mortality.
The usual method for spotting and assessing PPH is to observe and measure the blood loss directly, but earlier and more accurate detection techniques would be highly desirable, especially if they are inexpensive and record both external and internal bleeding.
A project at Washington University in St Louis (WUSTL) has now developed an optical monitor designed to be worn on the wrist that uses light perfusion to detect early signs of hemorrhage. The work and initial model trials were reported in Biomedical Optics Express.
"Postpartum hemorrhage most severely impacts people in low- and middle-income areas, who have limited access to high-quality medical diagnostics and treatments," said Christine O'Brien from WUSTL.
"We were inspired to develop an accessible tool that can be used in both low- and high-resource settings to detect this condition earlier than current methods. This work is the first step in the development and proof-of-concept testing of our initial prototype."
The device exploits a natural process called peripheral vasoconstriction, which takes place during hemorrhage and redirects blood flow towards vital organs and away from the extremities like the hands, feet and arms. This causes a decrease in blood flow in those peripheral locations, while blood flow remains normal in the body core.
WUSTL plans to detect this change in blood flow by observing the laser speckle flow index (LSFI), illuminating blood vessels in a wearer's wrist and detecting the speckle patterns caused by movement of blood cells within the vessels. Speckle and diffusion techniques are increasingly valuable in the detection of blood flow, and are primed for significant translation into clinical use.
Alerting mothers when they may be in danger
"Wearable laser speckle imaging sensors have been developed to provide real-time monitoring of perfusion and cardiovascular physiology, but to our knowledge there are no current laser speckle imaging wearables that are wireless, wrist-worn, or developed for use monitoring vasoconstriction in response to blood loss," commented the team in its paper.
The project's prototype device employs a 785-nanometer laser diode illuminating a spot 2.2 to 3.8 millimeters in diameter, with a 8 MP camera sensor built around a Raspberry Pi processor. Bespoke algorithms were developed to allow fast processing of speckle images via onboard video data processing.
After initial tests monitoring model fluid in tissue phantoms, the project used its LSFI platform in a swine animal model. As test animals lost blood, the device detected near-immediate continuous decreases in blood flow, and the response was almost perfectly linear according to the team.
In most animals the device also measured an increase in blood flow during intravenous injection with saline, as the added volume helped restore blood flow to the periphery. This shows that a wearable laser speckle imaging sensor could be used to monitor patients for early signs of postpartum hemorrhage and then also track their response to resuscitation efforts.
The next steps will include use of smaller lower-power lasers and testing the device with healthy volunteers, with plans to begin enrolling pregnant women in a clinical study at Washington University in the coming months. The team also hope to test the device’s performance in resource-limited settings.
"It could be useful for monitoring how patients are responding to treatment for a hemorrhage, and also offer a standalone tool for use at home or in other settings that alerts mothers giving birth when they may be in danger and should seek medical attention," commented WUSTL's Francesca Bonetta-Misteli.