Background: Near-infrared spectroscopy (NIRS) relative concentration signals contain ‘noise’ from physiological processes such as respiration and heart rate. Simultaneous assessment of NIRS and respiratory rate (RR) using a single sensor would facilitate a perfectly time-synced assessment of (cerebral) physiology. Our aim was to extract respiratory rate from cerebral NIRS intensity signals in neonates admitted to a neonatal intensive care unit (NICU). Methods: A novel algorithm, NRR (NIRS RR), is developed for extracting RR from NIRS signals recorded from critically ill neonates. In total, 19 measurements were recorded from ten neonates admitted to the NICU with a gestational age and birth weight of 38 ± 5 weeks and 3092 ± 990 g, respectively. We synchronously recorded NIRS and reference RR signals sampled at 100 Hz and 0.5 Hz, respectively. The performance of the NRR algorithm is assessed in terms of the agreement and linear correlation between the reference and extracted RRs, and it is compared statistically with that of two existing methods. Results: The NRR algorithm showed a mean error of 1.1 breaths per minute (BPM), a root mean square error of 3.8 BPM, and Bland–Altman limits of agreement of 6.7 BPM averaged over all measurements. In addition, a linear correlation of 84.5% (p < 0.01) was achieved between the reference and extracted RRs. The statistical analyses confirmed the significant (p < 0.05) outperformance of the NRR algorithm with respect to the existing methods. Conclusions: We showed the possibility of extracting RR from neonatal NIRS in an intensive care environment, which showed high correspondence with the reference RR recorded. Adding the NRR algorithm to a NIRS system provides the opportunity to record synchronously different physiological sources of information about cerebral perfusion and respiration by a single monitoring system. This allows for a concurrent integrated analysis of the impact of breathing (including apnea) on cerebral hemodynamics.

Orthostatic hypotension (OH) is highly prevalent in older adults and associated with dizziness, falls, lower physical and cognitive function, cardiovascular disease, and mortality. OH is currently diagnosed in a clinical setting with single-time point cuff measurements. Continuous blood pressure (BP) devices can measure OH dynamics but cannot be used for daily life monitoring. Near-infrared spectroscopy (NIRS) has potential diagnostic value in measuring cerebral oxygenation continuously over a longer time period, but this needs further validation. This study aimed to compare NIRS-measured (cerebral) oxygenation with continuous BP and transcranial Doppler-measured cerebral blood velocity (CBv) during postural changes. This cross-sectional study included 41 participants between 20 and 88 years old. BP, CBv, and cerebral (long channels) and superficial (short channels) oxygenated hemoglobin (O 2 Hb) were measured continuously during various postural changes. Pearson correlations between BP, CBv, and O 2 Hb were calculated over curves and specific characteristics (maximum drop amplitude and recovery). BP and O 2 Hb only showed good curve-based correlations (0.58–0.75) in the initial 30 s after standing up. Early (30–40 s) and 1-min BP recovery associated significantly with O 2 Hb, but no consistent associations were found for maximum drop amplitude and late (60–175 s) recovery values. Associations between CBv and O 2 Hb were poor, but stronger for long-channel than short-channel measurements. BP associated well with NIRS-measured O 2 Hb in the first 30 s after postural change. Stronger associations for CBv with long-channel O 2 Hb suggest that long-channel NIRS specifically reflects cerebral blood flow during postural transitions, necessary to better understand the consequences of OH such as intolerance symptoms.

Objective: Respiration is recognized as a systematic physiological interference in functional near-infrared spectroscopy (fNIRS). However, it remains unanswered as to whether it is possible to estimate the respiratory rate (RR) from such interference. Undoubtedly, RR estimation from fNIRS can provide complementary information that can be used alongside the cerebral activity analysis, e.g., sport studies. Thus, the objective of this paper is to propose a method for RR estimation from fNIRS. Our primary presumption is that changes in the baseline wander of oxygenated hemoglobin concentration (O2Hb) signal are related to RR. Methods: fNIRS and respiratory signals were concurrently collected from subjects during controlled breathing tasks at a constant rate from 0.1 Hz to 0.4 Hz. Firstly, the signal quality index algorithm is employed to select the best O2Hb signal, and then a band-pass filter with cut-off frequencies from 0.05 to 2 Hz is used to remove very low- and high-frequency artifacts. Secondly, troughs of the filtered O2Hb signal are localized for synthesizing the baseline wander (S1) using cubic spline interpolation. Finally, the fast Fourier transform of the S1 signal is computed, and its dominant frequency is considered as RR. In this paper, two different datasets were employed, where the first one was used for the parameter adjustment of the proposed method, and the second one was solely used for testing. Results: The low mean absolute error between the reference and estimated RRs for the first and second datasets (2.6 and 1.3 breaths per minute, respectively) indicates the feasibility of the proposed method for RR estimation from fNIRS. Significance: This paper provides a novel view on the respiration interference as a source of complementary information in fNIRS.

Continuous measurements of haemodynamic and oxygenation changes in free living animals remain elusive. However, developments in biomedical technologies may help to fill this knowledge gap. One such technology is continuous-wave near-infrared spectroscopy (CW-NIRS)—a wearable and non-invasive optical technology. Here, we develop a marinized CW-NIRS system and deploy it on elite competition freedivers to test its capacity to function during deep freediving to 107 m depth. We use the oxyhaemoglobin and deoxyhaemoglobin concentration changes measured with CW-NIRS to monitor cerebral haemodynamic changes and oxygenation, arterial saturation and heart rate. Furthermore, using concentration changes in oxyhaemoglobin 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, while some divers also showed considerable elevations in venous blood volumes close to the end of diving. Some freedivers also showed pronounced arterial deoxygenation, the most extreme of which resulted in an arterial saturation of 25%. Freedivers also displayed heart rate changes that were comparable to diving mammals both in magnitude and patterns of change. Finally, changes in cardiac waveform associated with heart rates less than 40 bpm were associated with 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 as well as free living animals. This article is part of the theme issue ‘Measuring physiology in free-living animals (Part II)’.

Background: Worldwide >2.3 billion individuals are affected by bladder disease. The current evaluative test is invasive, associated with complications and often declined. Non-invasive evaluation of bladder hemodynamics using continuous-wave near-infrared spectroscopy (NIRS) is an established technique. Recently, fNIRS was shown to detect activity in the brain regions previously identified by fMRI to relate to bladder sensation and control of voiding. We now report a system for simultaneous wireless fNIRS measurements of bladder and brain. Method: Two dual-wavelength (760/850 nm) fNIRS systems were used in parallel. A 23-channel array (35 mm interoptode distance) housed in a neoprene cap was positioned over the bilateral frontal cortex, and a 4-channel grid of 4 emitters and 1 detector taped to the skin over the bladder. Natural bladder filling to capacity and spontaneous voiding were monitored in two volunteer subjects. Proprietary software (Oxysoft v3.2.56) linked the devices, recorded raw optical data at 50 Hz and generated video and graphical displays of changes in oxygenated, de-oxygenated, and total hemoglobin. Results: Simultaneous brain and bladder data were captured in both subjects. Localized brain activity was evident on video as topographical colorimetric changes indicative of increases in oxyhemoglobin concentration in areas previously linked via fMRI to bladder sensation and function; signal intensity varied in relation to phases of voiding. In the bladder detrusor muscle oxyhemoglobin increased prior to permission to void; changes during uroflow differed between the symptomatic and asymptomatic subjects. Conclusion: Simultaneous wireless fNIRS of brain and bladder is feasible, and offers new physiological dimensions for evaluating bladder control and function.

Background: A requisite for fNIRS studies of cortical blood flow is that sufficient photons are transmitted transcutaneously for the fluctuations in cerebral hemoglobin oxygenation that occur during neuronal activation to be detected. Transmission is determined by the specifications of the fNIRS device, but also influenced by the characteristics of the skin. Epidermal pigments can attenuate photon transmission; the literature states that in dark skinned subjects some NIRS devices may not achieve sufficient photon migration to monitor cortical blood flow. Hence, as fNIRS use is spreading, we describe a simple head tilt maneuver where positional redistribution of cerebral blood volume will confirm if photon transmission is sufficient. Methods: A repetitive head tilt maneuver (bending forward from a seated position, hold for 30 seconds, returning to original position X 5) performed by a pigmented (African) subject and a non-pigmented (Caucasian) subject. A 23-channel portable fNIRS system with dual wavelength (750 and 860 nm) emitters and photodiode detectors was worn over the anterior cortex, and changes in oxy, deoxy and total hemoglobin concentration measured at 50 Hz. Results: Data from both subjects were compared and found to have a comparable pattern of change in oxyhemoglobin concentration and temporal response to the effects of head tilt; clear arterial pulsations and minimal noise were also evident. Conclusion: We suggest the head tilt maneuver described as a feasible test to confirm the adequacy of transcutaneous photon transmission where fNIRS studies are to be performed in subjects with pigmented skin to detect hemodynamic change in the cortex.

Investigation of marine mammal dive-by-dive blood distribution and oxygenation has been limited by a lack of noninvasive technology for use in freely diving animals. Here, we developed a noninvasive near-infrared spectroscopy (NIRS) device to measure relative changes in blood volume and haemoglobin oxygenation continuously in the blubber and brain of voluntarily diving harbour seals. Our results show that seals routinely exhibit preparatory peripheral vasoconstriction accompanied by increased cerebral blood volume approximately 15 s before submersion. These anticipatory adjustments confirm that blood redistribution in seals is under some degree of cognitive control that precedes the mammalian dive response. Seals also routinely increase cerebral oxygenation at a consistent time during each dive, despite a lack of access to ambient air. We suggest that this frequent and reproducible reoxygenation pattern, without access to ambient air, is underpinned by previously unrecognised changes in cerebral drainage. The ability to track blood volume and oxygenation in different tissues using NIRS will facilitate a more accurate understanding of physiological plasticity in diving animals in an increasingly disturbed and exploited environment.

In this article, we describe the development of a high throughput platform to spatially manipulate viable sperm for motility measurements and recovery of the best single sperm for fertilization purposes. Micro-contact printing was used to pattern islands of adhesive proteins (fibronectin) separated by sperm repellent species (Pluronic acid F-127) on commercially available polystyrene substrates. Following washing, arrays of viable single sperm were captured onto the islands demonstrating for the first time that sperm can be trapped by micro-contact printing with patterning efficiency of 90% while retaining 100% viability. These were then subjected to motility analysis whilst remaining spatially confined to the islands. Single sperm motility was assessed (n = 37) by software analysis measuring the number of rotations per second (degrees s⁻¹). The assignment of array coordinates allows the more active single sperm to be easily identified and recovered by a simple micromanipulator pipette aspiration step with automated possibility for assisted reproductive technologies or further quality correlation analysis. Taken together, we show for the first time a technique to simultaneously screen thousands of viable single sperm for motility assessment while retaining the ability for single species recovery for enhanced fertilization purposes.