Near-infrared spectroscopy as a tool for marine mammal research and care

This project was partially funded by the Department for Business, Energy and Industrial Strategy Offshore Energy Strategic Environmental Assessment Programme. Supplementary funding supporting JM was provided by the US Office of Naval Research (ONR) grant nos. N00014-18-1-2062 and N00014-20-1-2709. Supplementary funding supporting AF and JM was provided by the US Office of Naval Research (ONR) grant no. N00014-19-1-2560. Supplementary funding supporting BS-C, JK, and AR was provided by the US Office of Naval Research (ONR) grant no. N00014-19-1-1223.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.Publisher PDFPeer reviewe

Evaluating feasibility of functional near-infrared spectroscopy in dolphins

SIGNIFICANCE: Using functional near-infrared spectroscopy (fNIRS) in bottlenose dolphins (Tursiops truncatus) could help to understand how echolocating animals perceive their environment and how they focus on specific auditory objects, such as fish, in noisy marine settings. AIM: To test the feasibility of near-infrared spectroscopy (NIRS) in medium-sized marine mammals, such as dolphins, we modeled the light propagation with computational tools to determine the wavelengths, optode locations, and separation distances that maximize sensitivity to brain tissue. APPROACH: Using frequency-domain NIRS, we measured the absorption and reduced scattering coefficient of dolphin sculp. We assigned muscle, bone, and brain optical properties from the literature and modeled light propagation in a spatially accurate and biologically relevant model of a dolphin head, using finite-element modeling. We assessed tissue sensitivities for a range of wavelengths (600 to 1700 nm), source-detector distances (50 to 120 mm), and animal sizes (juvenile model 25% smaller than adult). RESULTS: We found that the wavelengths most suitable for imaging the brain fell into two ranges: 700 to 900 nm and 1100 to 1150 nm. The optimal location for brain sensing positioned the center point between source and detector 30 to 50 mm caudal of the blowhole and at an angle 45 deg to 90 deg lateral off the midsagittal plane. Brain tissue sensitivity comparable to human measurements appears achievable only for smaller animals, such as juvenile bottlenose dolphins or smaller species of cetaceans, such as porpoises, or with source-detector separations ≫100  mm in adult dolphins. CONCLUSIONS: Brain measurements in juvenile or subadult dolphins, or smaller dolphin species, may be possible using specialized fNIRS devices that support optode separations of >100  mm. We speculate that many measurement repetitions will be required to overcome hemodynamic signals originating predominantly from the muscle layer above the skull. NIRS measurements of muscle tissue are feasible today with source-detector separations of 50 mm, or even less.Publisher PDFPeer reviewe

Wearable near-infrared spectroscopy as a physiological monitoring tool for seals under anaesthesia

Chemical immobilisation of pinnipeds is a routine procedure in research and veterinary practice. Yet, there are inevitable risks associated with chemical immobilisation, and the physiological response to anaesthetic agents in pinnipeds remains poorly understood. The current study used wearable continuous-wave near-infrared spectroscopy (NIRS) data from 10 trials of prolonged anaesthesia (0.5 to 1.4 h) induced through ketamine and midazolam in five grey seals (Halichoerus grypus) involved in other procedures. The aim of this study was to (1) analyse the effect of each compound on heart rate, arterial oxygen saturation (SpO2), and relative concentration changes in oxygenated [ΔO2Hb] and deoxygenated haemoglobin [ΔHHb] in cerebral tissue and (2) to investigate the use of NIRS as a real-time physiological monitoring tool during chemical immobilisation. Average group responses of ketamine (n = 27) and midazolam (n = 11) administrations were modelled using generalised additive mixed models (GAMM) for each dependent variable. Following ketamine and midazolam administration, [ΔHHb] increased and [ΔO2Hb] remained relatively stable, which was indicative of apnoea. Periods of apnoea were confirmed from respiratory band data, which were simultaneously collected during drugging trials. Given that SpO2 remained at 97% during apnoea, we hypothesized that increasing cerebral [ΔHHb] was a result of venous congestion as opposed to decreased oxygen delivery. Changes in heart rate were limited and appeared to be driven by the individual pharmacological actions of each drug. Future research could include simultaneous measures of metabolic rate, such as the relative change in concentration of cytochrome-c-oxidase, to guide operators in determining when apnoea should be considered prolonged if changes in [ΔHHb] and [ΔO2Hb] occur beyond the limits recorded in this study. Our findings support the use of NIRS as real-time physiological monitoring tool during pinniped chemical immobilisation, which could assist veterinarians and researchers in performing safe anaesthetic procedures

Optical imaging and spectroscopy for the study of the human brain: status report

This report is the second part of a comprehensive two-part series aimed at reviewing an extensive and diverse toolkit of novel methods to explore brain health and function. While the first report focused on neurophotonic tools mostly applicable to animal studies, here, we highlight optical spectroscopy and imaging methods relevant to noninvasive human brain studies. We outline current state-of-the-art technologies and software advances, explore the most recent impact of these technologies on neuroscience and clinical applications, identify the areas where innovation is needed, and provide an outlook for the future directions

Optical imaging and spectroscopy for the study of the human brain: status report.

This report is the second part of a comprehensive two-part series aimed at reviewing an extensive and diverse toolkit of novel methods to explore brain health and function. While the first report focused on neurophotonic tools mostly applicable to animal studies, here, we highlight optical spectroscopy and imaging methods relevant to noninvasive human brain studies. We outline current state-of-the-art technologies and software advances, explore the most recent impact of these technologies on neuroscience and clinical applications, identify the areas where innovation is needed, and provide an outlook for the future directions

Application of near-infrared spectroscopy in human elite freedivers while deepdiving on a single breath hold

Funding Information: We would like to thank all volunteers for their kind participation. The studies were funded by a donation from Jennifer and Peter Francis, and by the Swedish Centre for Research in Sports. Further funding was received from the Office of Naval Research (N00014-19-1-1223).Near-infrared spectroscopy was used to observe the cerebral hemodynamic response of freedivers during single breath-hold training dives. We observed variability in hemodynamic progression, and heartbeat shape changes with diving depth.Publisher PD