Wearable NIRS Device Reveals How Seals Prepare to Dive

Scientists at the University of St. Andrews have created a wearable, noninvasive device based on near-infrared spectroscopy (NIRS) that can be used to investigate blood volume and oxygenation patterns in freely diving marine mammals, such as seals.

When mammals are submerged in water, they show a suite of cardiovascular responses such as reduced heart rate and constriction of peripheral blood vessels. The researchers hypothesized that NIRS could provide high-resolution, relative measures of oxygenated and deoxygenated hemoglobin within specific tissues, which then could be used to estimate changes in blood volume. They adapted NIRS technology for use on freely diving harbor seals to investigate blood volume and oxygenation patterns specifically in the brain and blubber, using a device that they called the PortaSeal.

Visualization illustrating the underlying concept of a three-optode-receiver-channel spatially resolved continuous-wave NIRS sensor. Heterodyning dual-wavelength light, visualized here in red, is emitted from (B) three light-emitting optodes in contact with a seal’s skin. Light passes through the underlying tissue before exiting the head, where it is detected by (A) a photodiode in contact with the seal’s skin. Increased distance between the optode and receiver channels provides deeper optical penetration within the underlying tissue. Courtesy of J. Chris McKnight et al./PLOS Biology.

With PortaSeal, the scientists were able to obtain detailed continuous NIRS data from four seals swimming freely in a quasi-natural foraging habitat. The device was superglued to the animals’ heads or shoulders and then easily removed to download the data.

A juvenile harbor seal. Courtesy of Monica Arso Civil, Sea Mammal Research Unit.

The results of the study were intriguing, said the researchers: Seals routinely constrict their peripheral blood vessels, accompanied by increased cerebral blood volume, approximately 15 seconds before submersion. These anticipatory adjustments suggest that blood redistribution in seals is under some degree of cognitive control and is not just a reflex response to submersion. “Getting this insight with noninvasive wearable technology from the biomedical field offers many exciting future research avenues,” said research fellow J. Chris McKnight.

The research was published in PLOS Biology (https://doi.org/10.1371/journal.pbio.3000306).