When the human brain goes diving:
using near-infrared spectroscopy to measure cerebral and systemic cardiovascular responses to deep, breath-hold diving in elite freedivers
J Chris McKnight ... Erika Schagatay 2021
Philosophical Transactions of the Royal Society B.
https://doi.org/10.1098/rstb.2020.0349

Continuous measurements of haemodynamic & oxygenation changes in free living animals remain elusive.
Developments in bio-medical technologies may help to fill this knowledge gap.
One such technology is continuous-wave near-infrared spectroscopy (CW-NIRS), a wearable & non-invasive optical technology.

Here, we develop a marinized CW-NIRS system, and deploy it on elite competition free-divers, to test its capacity to function during deep freediving to 107 m depth.
We use the oxy- & deoxy-haemoglobin concentration changes measured with CW-NIRS, to monitor cerebral haemodynamic changes & oxygenation, arterial saturation & heart rate (HR).
Using concentration changes in oxy-Hb engendered by cardiac pulsation, we demonstrate the ability to conduct additional feature exploration of cardiac-dependent haemodynamic changes.
Freedivers showed cerebral haemodynamic changes characteristic of apnoeic diving,
some divers also showed considerable elevations in venous blood volumes close to the end of diving.
Some freedivers also showed pronounced arterial de-oxygenation, the most extreme of which resulted in an arterial saturation of 25 %.
Freedivers also displayed HR changes comparable to diving mammals, both in magnitude & patterns of change.
Changes in cardiac wave-form ass.x HRs <40/minute were ass.x changes indicative of a reduction in vascular compliance.
The success here of CW-NIRS to non-invasively measure a suite of physiological phenomenon in a deep-diving mammal highlights its efficacy as a future physiological monitoring tool for human freedivers & free living animals.