Abstract
Developments in wearable human medical and sports health trackers has offered new solutions to challenges encountered by eco-physiologists attempting to measure physiological attributes in freely moving animals. Near-infrared spectroscopy (NIRS) is one such solution that has potential as a powerful physio-logging tool to assess physiology in freely moving animals. NIRS is a non-invasive optics-based technology, that uses non-ionizing radiation to illuminate biological tissue and measures changes in oxygenated and deoxygenated hemoglobin concentrations inside tissues such as skin, muscle, and the brain. The overall footprint of the device is small enough to be deployed in wearable physio-logging devices. We show that changes in hemoglobin concentration can be recorded from bottlenose dolphins and gray seals with signal quality comparable to that achieved in human recordings. We further discuss functionality, benefits, and limitations of NIRS as a standard tool for animal care and wildlife tracking for the marine mammal research community.
Highlights
The field of “biologging” has largely focused on describing where animals go in space and time
We recently demonstrated the utility of CW-Near-infrared spectroscopy (NIRS) in voluntarily diving seals and breath-hold diving humans performing deep dives (>100 m) (McKnight et al, 2019, 2021a,b)
We outline the functionality and optical theory for how CW-NIRS works, and demonstrate its feasibility by translating approaches developed for human measurements to different marine mammal species
Summary
The field of “biologging” (i.e., logging/transmission of biological variables via devices attached to animals) has largely focused on describing where animals go in space and time. Combining NIRS’ non-invasive nature, relatively small size, and the possibility of integrating it into existing animal-borne dataloggers and telemetry systems, makes CW-NIRS a promising technology to develop for physiologging research In this perspective, we outline the functionality and optical theory for how CW-NIRS works, and demonstrate its feasibility by translating approaches developed for human measurements to different marine mammal species. Is a function of absolute optical properties of absorption (μa) and reduced scattering coefficient (μs), known from literature or measurable with more advanced NIRS devices It relates the average distance traveled of light through the tissue, to r. The respiratory signal shows that HbO and HbR trend in opposite directions immediately after a respiratory event This indicates a change in blood flow, leading to a rapid oxygenation of the brain tissue, consistent with rapid and deep respiration events that are common in gray seals (Figure 2B). The hemodynamic changes during cardiac pulsations and respiration observed in the muscle layers indicate a qualitatively comparable signal strength to human and gray seal hemodynamic measurements (Figure 2)
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