Into the Deep with Submersible NIRS
Seals are adept ocean divers... Now, near-infrared spectroscopy provides clues as to how they survive extreme depths.
Matt Hallam | | Quick Read
Did you know that the deepest recorded seal dive is over 2.3 kilometers? Here, water pressure reaches approximately 240 times the air pressure at the surface, and temperatures plummet to near zero.
Dedicated divers (like the seal) have evolution to thank for their talent – but exactly what physiological changes allow them to thrive rather than just survive? Such knowledge could be used to further our understanding of human issues related to breath-hold diving – such as shallow water blackout – allowing us to better protect free divers.
To that end, Chris McKnight and colleagues attached near-infrared spectroscopy (NIRS) devices to juvenile harbor seals from Moray Firth, Scotland, and recorded oxy- and deoxyhemoglobin levels non-invasively during voluntary dives (1). Peripheral cardiovascular changes – a hallmark of the diving response that allows blood redistribution to essential organs – occurred before diving and cerebral reoxygenation occurred during diving; the team believes that the former may facilitate the latter by increasing venous drainage from the brain.
McKnight was surprised by both findings: “We expected peripheral blood changes to occur at the point of submersion, and thought that cerebral oxygenation would simply decline throughout diving – it appears that seals are more physiologically sophisticated divers than expected.” Yet, McKnight also believes that these apparently unique capabilities may be more widespread in the animal kingdom than we currently know.
The next steps are to study circulatory and oxygenation changes in other diving animals. Humans – especially competitive free-divers and indigenous diving communities in Asia – are of particular interest to determine how we protect ourselves against cerebral hypoxia. Regarding further work in seals, “Our longer-term goal is to use larger NIRS arrays to highlight which senses seals use to locate and catch prey, and how they balance depleting oxygen stores with the need to maintain brain functions at depths of 2 kilometers,” says McKnight.
- JC McKnight et al., “Shining new light on mammalian diving physiology using wearable near-infrared spectroscopy", PLoS Biol, 17, e3000306 (2019). DOI: 10.1371/journal.pbio.3000306