Continuous-wave Near-infrared Spectroscopy Research Articles

Estimation of differential pathlength factor from NIRS measurement in skeletal muscle

The utilization of continuous wave (CW) near-infrared spectroscopy (NIRS) device to measure non-invasively muscle oxygenation in healthy and disease states is limited by the uncertainties related to the differential path length factor (DPF). DPF value is required to quantify oxygenated and deoxygenated heme groups’ concentration changes from measurement of optical densities by NIRS. An integrated approach that combines animal and computational models of oxygen transport and utilization was used to estimate the DPF value in situ. The canine model of muscle oxidative metabolism allowed measurement of both venous oxygen content and tissue oxygenation by CW NIRS under different oxygen delivery conditions. The experimental data obtained from the animal model were integrated in a computational model of O2 transport and utilization and combined with Beer-Lambert law to estimate DPF value in contracting skeletal muscle. A 2.1 value was found for DPF by fitting the mathematical model to the experimental data obtained in contracting muscle (T3) (Med.Sci.Sports.Exerc.48(10):2013–2020,2016). With the estimated value of DPF, model simulations well predicted the optical density measured by NIRS on the same animal model but with different blood flow, arterial oxygen contents and contraction rate (J.Appl.Physiol.108:1169–1176, 2010 and 112:9–19,2013) and demonstrated the robustness of the approach proposed in estimating DPF value. The approach used can overcome the semi-quantitative nature of the NIRS and estimate non-invasively DPF to obtain an accurate concentration change of oxygenated and deoxygenated hemo groups by CW NIRS measurements in contracting skeletal muscle under different oxygen delivery and contraction rate.

Assessing changes in regional cerebral hemodynamics in adults with a high-density full-head coverage time-resolved near-infrared spectroscopy device.

Cerebral oximeters have the potential to detect abnormal cerebral blood oxygenation to allow for early intervention. However, current commercial systems have two major limitations: (1)spatial coverage of only the frontal region, assuming that surgery-related hemodynamic effects are global and (2)susceptibility to extracerebral signal contamination inherent to continuous-wave near-infrared spectroscopy (NIRS). This work aimed to assess the feasibility of a high-density, time-resolved (tr) NIRS device (Kernel Flow) to monitor regional oxygenation changes across the cerebral cortex during surgery. The Flow system was assessed using two protocols. First, digital carotid compression was applied to healthy volunteers to cause a rapid oxygenation decrease across the ipsilateral hemisphere without affecting the contralateral side. Next, the system was used on patients undergoing shoulder surgery to provide continuous monitoring of cerebral oxygenation. In both protocols, the improved depth sensitivity of trNIRS was investigated by applying moment analysis. A dynamic wavelet filtering approach was also developed to remove observed temperature-induced signal drifts. In the first protocol ( years; five females, five males), hair significantly impacted regional sensitivity; however, the enhanced depth sensitivity of trNIRS was able to separate brain and scalp responses in the frontal region. Regional sensitivity was improved in the clinical study given the age-related reduction in hair density of the patients ( years; 14 females, 13 males). In five patients who received phenylephrine to treat hypotension, different scalp and brain oxygenation responses were apparent, although no regional differences were observed. The Kernel Flow has promise as an intraoperative neuromonitoring device. Although regional sensitivity was affected by hair color and density, enhanced depth sensitivity of trNIRS was able to resolve differences in scalp and brain oxygenation responses in both protocols.

Intratracheal cobinamide (vitamin B12 analog) administration increases survivability in rabbits exposed to a lethal dose of inhaled hydrogen sulfide

Background Hydrogen sulfide is a highly toxic, flammable, and colorless gas. Hydrogen sulfide has been identified as a potential terrorist chemical threat agent in mass-casualty events. Our previous studies showed that cobinamide, a vitamin B12 analog, effectively reverses the toxicity from hydrogen sulfide poisoning. In this study, we investigate the effectiveness of intratracheally administered cobinamide in treating a lethal dose hydrogen sulfide gas inhalation and compare its performance to saline control administration Methods A total of 53 pathogen-free New Zealand White rabbits were used for this study. Four groups were compared: (i) received no saline solution or drug intratracheally (n = 15), (ii) slow drip saline intratracheally (n = 15), (iii) fast drip saline intratracheally (n = 15), and (iv) slow drip cobinamide intratracheally (n = 8). Blood pressure was continuously monitored, and deoxy- and oxyhemoglobin concentration changes were monitored in real-time in vivo using continuous wave near-infrared spectroscopy. Results The mean (± standard deviation) weight for all animals (n = 53) was 3.87 ± 0.10 kg. The survival rates of the slow cobinamide and the fast saline groups were 75 percent and 60 percent, respectively, while the survival rates in the slow saline and control groups were 26.7 percent and 20 percent, respectively. A log-rank (Mantel-Cox) test showed that survival in fast saline and slow cobinamide groups were significantly greater than those of no saline control and slow saline groups (P < 0.05). The slow and no saline control groups were not significantly different (P = 0.59). The slow cobinamide group did significantly better than the slow saline group (P = 0.021). Discussion The ability to use intratracheal cobinamide as an antidote to hydrogen sulfide poisoning is a novel approach to mass-casualty care. The major limitations of this study are that it was conducted in a single species at a single inhaled hydrogen sulfide concentration. Repeated investigations in other species and at varying levels of hydrogen sulfide exposure will be needed before any definitive recommendations can be made. Conclusions We demonstrated that intratracheal cobinamide and fast saline drip improved survival for hydrogen sulfide gas inhalation in rabbit models. Although further study is required, our results suggest that intratracheal administration of cobinamide and fast saline may be useful in hydrogen sulfide mass-casualty events.

Self-calibrated pulse oximetry algorithm based on photon pathlength change and the application in human freedivers.

Pulse oximetry estimates the arterial oxygen saturation of hemoglobin () based on relative changes in light intensity at the cardiac frequency. Commercial pulse oximeters require empirical calibration on healthy volunteers, resulting in limited accuracy at low oxygen levels. An accurate, self-calibrated method for estimating is needed to improve patient monitoring and diagnosis. Given the challenges of calibration at low levels, we pursued the creation of a self-calibrated algorithm that can effectively estimate across its full range. Our primary objective was to design and validate our calibration-free method using data collected from human subjects. We developed an algorithm based on diffuse optical spectroscopy measurements of cardiac pulses and the modified Beer-Lambert law (mBLL). Recognizing that the photon mean pathlength () varies with related absorption changes, our algorithm aligns/fits the normalized (across wavelengths) obtained from optical measurements with its analytical representation. We tested the algorithm with human freedivers performing breath-hold dives. A continuous-wave near-infrared spectroscopy probe was attached to their foreheads, and an arterial cannula was inserted in the radial artery to collect arterial blood samples at different stages of the dive. These samples provided ground-truth via a blood gas analyzer, enabling us to evaluate the accuracy of estimation derived from the NIRS measurement using our self-calibrated algorithm. The self-calibrated algorithm significantly outperformed the conventional method (mBLL with a constant ratio) for estimation through the diving period. Analyzing 23 ground-truth data points ranging from 41% to 100%, the average absolute difference between the estimated and the ground truth is for our algorithm, significantly lower than the observed with the conventional approach. By factoring in the variations in the spectral shape of relative to , our self-calibrated algorithm enables accurate estimation, even in subjects with low levels.

Exploring Near Infrared Spectroscopy As a Tool for Monitoring Tissue Hemodynamics for Patients with Sickle Cell Disease

Sickle cell disease (SCD) is a genetic disorder that has higher prevalence in people of African ancestry. In the United States, SCD affects about 100,000 people and 1 in 365 African Americans. Sickled red blood cells (RBCs) have a shorter life span and are rigid, causing chronic hemolytic anemia and vaso-occlusive crises. There is a need for accessible diagnostic and monitoring technologies to characterize hemodynamic health, especially for patients with SCD. Near infrared spectroscopy (NIRS) is a noninvasive optical technique that uses light in the near infrared range (650 - 900 nm) to gain information from tissue absorption and light scattering. The purpose of this study is to show that NIRS is sensitive to differences in tissue hemodynamics between patients with SCD and healthy population. We enrolled adults (age ≥ 18 years) of African descent who were not recently transfused under protocol NCT05604547. Baseline hemodynamics and day-to-day variability were quantified in 10 SCD patients with HbSS (six male, four female) and six healthy, ethnically matched participants (four male, two female). We assessed participants with affixed transmission speckle analysis (ATSA) and a dual system frequency domain-NIRS (FD-NIRS) with diffuse correlation spectroscopy (DCS) device to measure blood flow and hemoglobin concentration. Participants underwent a respiratory challenge, three sets of breath holds, with the optical probe on their forehead. Then, the participants underwent a vascular occlusion challenge, a three-minute brachial blood pressure cuff occlusion at 200 mmHg, with the optical probe on their forearm. We also measured skin and adipose tissue thickness (SATT) of the forearm site with ultrasound. Two of the healthy control participants were excluded from the skeletal muscle analysis due to SATT &amp;gt; 8 mm. A Mann-Whitney significance test was used to evaluate the results. From these measurements, we acquired the concentration of oxygenated (O 2Hb), deoxygenated (HHb), and total hemoglobin (tHb); blood flow index (BFi); and tissue oxygen saturation (StO 2) for cerebral and skeletal muscle. The cerebral StO 2 in the SCD cohort was lower than the control group, 55.5 ± 7.4% versus 66.9 ± 2.5% (p = 0.003), respectively. Skeletal muscle StO 2 in the SCD cohort was lower than that in control, 59.2 ± 5.8% versus 66.4 ± 6.7%, respectively, but the difference was not significant (p = 0.19). The muscle O 2Hb in the SCD cohort was lower compared to control: 32.7 ± 6.5 µM versus 51.0 ± 9.2 µM (p = 0.01), respectively. The muscle tHb had a similar trend, with the SCD cohort measuring 55.8 ± 12.0 µM and the control group measuring 76.5 ± 9.0 µM (p = 0.03). The SCD cohort was also found to have lower overall muscle BFi, averaging 5.37 x 10 -9 ± 3.47 x 10 -9 cm/s, whereas the control group had an average of 1.90 x 10 -8 ± 1.33 x 10 -8 cm/s (p = 0.004). We also calculated hemodynamic markers, such as components of the occlusion recovery. The post-occlusion O 2Hb recovery slope for the SCD cohort was 0.31 ± 0.19 µM/s compared with control group at 1.56 ± 0.75 µM/s (p = 0.004). The goal of this study is to compare baseline vascular hemodynamics between patients with SCD and ethnically matched healthy controls. This study is ongoing and preliminary data analysis suggests impaired cardiovascular health in SCD subjects. The cerebral StO 2, muscle O 2Hb, and tHb in the SCD cohort is hypothesized to be a result of the reduced ability of sickled RBC to carry oxygen. There was a significant difference in the cerebral StO 2 but not in the skeletal muscle StO 2, suggesting that there are more dynamic changes seen in the brain than the muscle. This is consistent with previous work using commercial, continuous-wave NIRS systems for a SCD cohort (Barriteau et al. 2022) that also reported significantly lower cerebral StO 2 and lower trending, but not significant, muscle StO 2 values.The post-occlusion O 2Hb recovery upslope is hypothesized to be slower for the SCD cohort due to reduced endothelial function. We plan to assess repeatability of intra-individual NIRS parameters and to compare the non-invasive hemodynamic metrics to clinical markers, such as blood Hb and echocardiogram. These preliminary results indicate that NIRS is sensitive to changes in hemodynamic variations between SCD patients and healthy controls and, therefore, has the potential to serve as a point-of-care technology for individualized clinical management for patients with SCD.

Eccentric cycling involves greater mental demand and cortical activation of the frontoparietal network.

Eccentric, compared to concentric exercise, is proposed to involve different neuro-motor processing strategies and a higher level of mental demand. This study compared eccentric and concentric cycling at matched perceived effort and torque for the mental demand and related-cortical activation patterns. Nineteen men (30 ± 6 years) performed four different 5-min cycling conditions at 30 RPM on a semi-recumbent isokinetic cycle ergometer: (1) concentric at a moderate perceived effort (23 on the CR100® scale) without torque feedback; (2) concentric and (3) eccentric at the same average torque produced in the first condition; and (4) eccentric at the same moderate perceived effort than the first concentric condition. The conditions two to four were randomized. After each condition, mental demand was monitored using the NASA Task Load Index scale. Changes in oxy-(O2 Hb) and deoxy-(HHb) hemoglobin during exercise were measured over both prefrontal cortices and the right parietal lobe from a 15-probe layout using a continuous-wave NIRS system. Mental demand was significantly higher during eccentric compared to concentric cycling (+52%, p = 0.012) and when the exercise intensity was fixed by the torque rather than the perceived effort (+70%, p < 0.001). For both torque- or perceived effort-matched exercises, O2 Hb increased significantly (p < 0.001) in the left and right prefrontal cortices, and right parietal lobe, and HHb decreased in the left, and right, prefrontal cortices during eccentric compared to concentric cycling. This study supports that acute eccentric cycling, compared to concentric cycling, involves a higher mental demand, and frontoparietal network activation.

Impact of aerobic fitness status, menstrual cycle phase, and oral contraceptive use on exercise substrate oxidation and metabolic flexibility in females.

The influence of menstrual cycle phase and fitness status on metabolism during high-intensity interval exercise (HIIE) was assessed. Twenty-five females (24.4 (3.6) years) were categorized by normal menstrual cycle (n=14) vs. oral contraceptive (OC) use (n=11) and by aerobic fitness, high-fitness females (HFF; n=13) vs. low-fitness females (LFF; n=12). HIIE was four sets of four repetitions with a 3min rest between intervals on a cycle ergometer at a power output halfway between the ventilatory threshold and V̇O2peak and performed during follicular (FOL: days 2-7 or inactive pills) and luteal phases (LUT: day ∼21 or 3rd week of active pills). Substrate oxidation was assessed via indirect calorimetry, blood lactate via finger stick, and recovery of skeletal muscle oxidative metabolism (mV̇O2) via continuous-wave near-infrared spectroscopy. HFF oxidized more fat (g·kg-1) during the full session (FOL: p=0.050, LUT: p=0.001), high intervals (FOL: p=0.048, LUT: p=0.001), low intervals (FOL: p=0.032, LUT: p=0.024), and LUT recovery (p=0.033). Carbohydrate oxidation area under the curve was greater in HFF during FOL (FOL: p=0.049, LUT: p=0.124). Blood lactate was lower in LFF in FOL (p≤0.05) but not in LUT. Metabolic flexibility (Δ fat oxidation g·kg-1·min-1) was greater in HFF than LFF during intervals 2-3 in FOL and 1-4 in LUT (p≤0.05). Fitness status more positively influences exercise metabolic flexibility during HIIE than cycle phase or OC use.

Correlation between cerebral hemodynamic functional near-infrared spectroscopy and positron emission tomography for assessing mild cognitive impairment and Alzheimer's disease: An exploratory study.

This study was performed to investigate the usefulness of functional near-infrared spectroscopy (fNIRS) by conducting a comparative analysis of hemodynamic activation detected by fNIRS and positron emission tomography (PET) and magnetic resonance imaging (MRI) in patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD). Participants were divided into four groups: the subjective memory impairment (SMI), amnestic MCI (aMCI), non-amnestic MCI (naMCI), and AD groups. We recorded the hemodynamic response during the semantic verbal fluency task (SVFT) using a commercial wireless continuous-wave NIRS system. The correlation between the parameters of the neuroimaging assessments among the groups was analyzed. Region of interest-based comparisons showed that the four groups had significantly different hemodynamic responses during SVFT in the bilateral dorsolateral prefrontal cortex (DLPFC). The linear mixed effect model result indicates that the mean ΔHbO2 from the bilateral DLPFC regions showed a significant positive correlation to the overall FDG-PET after controlling for age and group differences in the fNIRS signals. Amyloid PET signals tended to better differentiate the AD group from other groups, and fNIRS signals tended to better differentiate the SMI group from other groups. In addition, a comparison between the group pairs revealed a mirrored pattern between the hippocampal volume and hemodynamic response in the DLPFC. The hemodynamic response detected by fNIRS showed a significant correlation with metabolic and anatomical changes associated with disease progression. Therefore, fNIRS may be considered as a screening tool to predict the hemodynamic and metabolic statuses of the brain in patients with MCI and AD.

Predictive value of forearm muscle oxygenation parameters for climbing-specific finger endurance and competitive climbing performance

PurposeNear-infrared spectroscopy (NIRS) is a valid and reliable method to assess forearm muscle oxygenation in sport climbing, focusing on evaluating single parameters. The study assessed the predictive value of various NIRS parameters in climbing-specific settings, during intermittent finger endurance testing and in a simulated climbing competition.Methods52 recreational climbers (28.5 ± 6.3 y) performed an intermittent finger endurance test and 10 competitive climbers (20.2 ± 6.3 y) participated in a simulated lead climbing competition. Continuous-wave NIRS were used to assess oxygenation and blood volume changes.ResultsNIRS parameters predicted 26.4% of the variance in the intermittent test, with mean minima and maxima of O2Hb and mean maxima of TSI% of the single repetitions being the predictors. No significant differences existed between the last valid and the first nonvalid repetition on the combined dependent variable. For the simulated competition, a statistically significant difference between the 20 s intervals on the combined dependent variables was found with posthoc testing showing significant univariate within-subjects effects for HHb, tHb & TSI, but not for O2Hb.ConclusionThe results indicate that for the intermittent test, high re- and deoxygenation abilities, and for the climbing competition, the accumulation of HHb concentration levels have the highest predictability.

Robustness of tissue oxygenation estimates by continuous wave space-resolved near infrared spectroscopy.

Continuous wave near infrared spectroscopy (CW-NIRS) is widely exploited in clinics to estimate skeletal muscles and brain cortex oxygenation. Spatially resolved spectroscopy (SRS) is generally implemented in commercial devices. However, SRS suffers from two main limitations: the a priori assumption on the spectral dependence of the reduced scattering coefficient [] and the modeling of tissue as homogeneous. We studied the accuracy and robustness of SRS NIRS. We investigated the errors in retrieving hemodynamic parameters, in particular tissue oxygen saturation (), when was varied from expected values, and when layered tissue was considered. We simulated hemodynamic variations mimicking real-life scenarios for skeletal muscles. Simulations were performed by exploiting the analytical solutions of the photon diffusion equation in different geometries: (1)semi-infinite homogeneous medium and constant ; (2)semi-infinite homogeneous medium and linear changes in ; (3)two-layered media with a superficial thickness , 7.5, 10mm and constant . All simulated data were obtained at source-detector distances , 40, 45mm, and analyzed with the SRS approach to derive hemodynamic parameters (concentration of oxygenated and deoxygenated hemoglobin, total hemoglobin concentration, and tissue oxygen saturation, ) and their relative error. Variations in affect the estimated (up to ), especially if changes are different at the two wavelengths. However, the main limitation of the SRS method is the presence of a superficial layer: errors strongly larger than 20% were retrieved for the estimated when the superficial thickness exceeds 5mm. These results highlight the need for more sophisticated strategies (e.g., the use of multiple short and long distances) to reduce the influence of superficial tissues in retrieving hemodynamic parameters and warn the SRS users to be aware of the intrinsic limitation of this approach, particularly when exploited in the clinical environment.

Evaluation of inter-rater and test-retest reliability for near-infrared spectroscopy reactive hyperemia measures.

Near-infrared spectroscopy (NIRS) is a non-invasive tool used to measure blood flow in peripheral tissues. More information on inter-rater agreement and test-retest reliability of NIRS-based reperfusion assessments is needed. To assess inter-rater agreement for NIRS based data analysis, and evaluate the measurement's reliability across days. On three separate days (average days between visits 1 and 3: 19.4±6.9days), participants' (N=15 males, 22±2yr.) post-occlusion reactive hyperemia (PORH) was measured in the left gastrocnemius muscle using Continuous-Wave NIRS (CW-NIRS). A blood pressure cuff was placed proximal to the knee and inflated to occlude lower leg blood flow for 5min. The following CW-NIRS parameters were selected: (1) percent saturation in HbO2 (StO2%) at baseline; (2) the O2Hb range used to normalize the NIRS signal; (3) the time for the O2Hb signal to reach 50% peak post-occlusion hyperemia (T1/2), and (4) the post peak hyperemic O2Hb recovery slope (O2REC-SLP). Absolute agreement between the two analysts was calculated using two-way random effects Intraclass Correlation Coefficients (ICC2,1). Consistency between analysts and across days was calculated using two-way mixed models (ICC3,1). Mean and 95% confidence intervals (CI) of ICCs are reported. Coefficient of variation (CV) and standard error of the measurement (SEM) are reported. The ICC2,1 data indicated "adequate" to "excellent" absolute agreement between the two NIRS analysts. ICC2,3 data indicated "adequate" to "good" reliability across visits. The CV and SEM for rater 1 and rater 2 across visit were StO2 (CV: 3.79%±2.71% and 4.50%±2.37%; SEM: 3.42 and 3.82), O2Hb range (CV: 10.50±5.93 and 12.79±12.41; SEM: 3.26 and 4.71), T1/2 (CV: 11.15%±5.52% and 10.96%±4.50; SEM: 1.22 and 1.11), and O2REC-SLP (CV: 19.49%±9.99% and 18.45%±9.48%; SEM: 0.04 and 0.04). It is concluded that NIRS parameters assessed show adequate reliability between analysts and across three visits. It is recommended, when feasible and because of the absence of 100% reliability, that investigators employ more than one rater for scoring at least a portion of the data across each trial in a study's control condition in order to have the ability to estimate the magnitude of error attributable to imperfect reliability.

Review of recent advances in frequency-domain near-infrared spectroscopy technologies [Invited

Over the past several decades, near-infrared spectroscopy (NIRS) has become a popular research and clinical tool for non-invasively measuring the oxygenation of biological tissues, with particular emphasis on applications to the human brain. In most cases, NIRS studies are performed using continuous-wave NIRS (CW-NIRS), which can only provide information on relative changes in chromophore concentrations, such as oxygenated and deoxygenated hemoglobin, as well as estimates of tissue oxygen saturation. Another type of NIRS known as frequency-domain NIRS (FD-NIRS) has significant advantages: it can directly measure optical pathlength and thus quantify the scattering and absorption coefficients of sampled tissues and provide direct measurements of absolute chromophore concentrations. This review describes the current status of FD-NIRS technologies, their performance, their advantages, and their limitations as compared to other NIRS methods. Significant landmarks of technological progress include the development of both benchtop and portable/wearable FD-NIRS technologies, sensitive front-end photonic components, and high-frequency phase measurements. Clinical applications of FD-NIRS technologies are discussed to provide context on current applications and needed areas of improvement. The review concludes by providing a roadmap toward the next generation of fully wearable, low-cost FD-NIRS systems.

The Influence of Extracerebral Tissue on Continuous Wave Near-Infrared Spectroscopy in Adults: A Systematic Review of In Vivo Studies.

Near-infrared spectroscopy (NIRS) is a non-invasive technique for measuring regional tissue haemoglobin (Hb) concentrations and oxygen saturation (rSO2). It may be used to monitor cerebral perfusion and oxygenation in patients at risk of cerebral ischemia or hypoxia, for example, during cardiothoracic or carotid surgery. However, extracerebral tissue (mainly scalp and skull tissue) influences NIRS measurements, and the extent of this influence is not clear. Thus, before more widespread use of NIRS as an intraoperative monitoring modality is warranted, this issue needs to be better understood. We therefore conducted a systematic review of published in vivo studies of the influence of extracerebral tissue on NIRS measurements in the adult population. Studies that used reference techniques for the perfusion of the intra- and extracerebral tissues or that selectively altered the intra- or extracerebral perfusion were included. Thirty-four articles met the inclusion criteria and were of sufficient quality. In 14 articles, Hb concentrations were compared directly with measurements from reference techniques, using correlation coefficients. When the intracerebral perfusion was altered, the correlations between Hb concentrations and intracerebral reference technique measurements ranged between |r| = 0.45-0.88. When the extracerebral perfusion was altered, correlations between Hb concentrations and extracerebral reference technique measurements ranged between |r| = 0.22-0.93. In studies without selective perfusion modification, correlations of Hb with intra- and extracerebral reference technique measurements were generally lower (|r| < 0.52). Five articles studied rSO2. There were varying correlations of rSO2 with both intra- and extracerebral reference technique measurements (intracerebral: |r| = 0.18-0.77, extracerebral: |r| = 0.13-0.81). Regarding study quality, details on the domains, participant selection and flow and timing were often unclear. We conclude that extracerebral tissue indeed influences NIRS measurements, although the evidence (i.e., correlation) for this influence varies considerably across the assessed studies. These results are strongly affected by the study protocols and analysis techniques used. Studies employing multiple protocols and reference techniques for both intra- and extracerebral tissues are therefore needed. To quantitatively compare NIRS with intra- and extracerebral reference techniques, we recommend applying a complete regression analysis. The current uncertainty regarding the influence of extracerebral tissue remains a hurdle in the clinical implementation of NIRS for intraoperative monitoring. The protocol was pre-registered in PROSPERO (CRD42020199053).

Near-Infrared Spectroscopy for the In Vivo Monitoring of Biodegradable Implants in Rats.

Magnesium (Mg) alloys possess unique properties that make them ideal for use as biodegradable implants in clinical applications. However, reports on the in vivo assessment of these alloys are insufficient. Thus, monitoring the degradation of Mg and its alloys in vivo is challenging due to the dynamic process of implant degradation and tissue regeneration. Most current works focus on structural remodeling, but functional assessment is crucial in providing information about physiological changes in tissues, which can be used as an early indicator of healing. Here, we report continuous wave near-infrared spectroscopy (CW NIRS), a non-invasive technique that is potentially helpful in assessing the implant-tissue dynamic interface in a rodent model. The purpose of this study was to investigate the effects on hemoglobin changes and tissue oxygen saturation (StO2) after the implantation of Mg-alloy (WE43) and titanium (Ti) implants in rats' femurs using a multiwavelength optical probe. Additionally, the effect of changes in the skin on these parameters was evaluated. Lastly, combining NIRS with photoacoustic (PA) imaging provides a more reliable assessment of tissue parameters, which is further correlated with principal component analysis.

Pecan-enriched diet improves cholesterol profiles and enhances postprandial microvascular reactivity in older adults

Pecan-enriched diets have been linked to improved lipid metabolism; however, the impact of pecans on vascular health has yet to be examined. We hypothesized that 4 weeks of a pecan-enriched diet would improve fasting and postprandial blood lipids and vascular function compared with a nut-free diet. In this randomized control study, 44 older adults (59 ± 6 years) consumed 68 g of pecans/d (pecan; n = 21) or avoided all nuts (control; n = 23) for 4 weeks. At pre- and post-diet visits, fasting and postprandial blood lipids, macrovascular (by flow-mediated dilation), and microvascular (tissue saturation index reactive hyperemia [RH] kinetics by continuous-wave near-infrared spectroscopy) function were assessed. From the pre- to post-diet visit, there were greater reductions in fasting total cholesterol (pecan: –14 ± 4.0 vs control: –0.2 ± 5.4 mg/dL; P = .04), low-density lipoprotein (LDL) cholesterol (pecan: –15 ± 3.7 vs control: +1.9 ± 4.4 mg/dL; P = .01), non–high-density lipoprotein cholesterol (pecan: –15 ± 3.6 vs control: –0.5 ± 4.8 mg/dL; P = .02), LDL particle number (pecan: –126 ± 51 vs control: +43 ± 42 nmol/L; P = .01), and LDL medium (pecan: –34 ± 13 vs control: +16 ± 11 nmol/L; P < .01), for pecan vs control. Further, postprandial triglyceride was suppressed for pecan (P = .01) compared with control (P = .78). Postprandial RH slope (P = .04) and RH time to half (P = .004) was different by group, driven by improvements in pecan vs control. However, fasting macro- and microvascular function was unaffected. Daily pecan consumption for 4 weeks improved fasting and postprandial blood lipids and microvascular reactivity in older adults. Because changes in microvascular function typically precipitate macrovascular changes, long-term pecan consumption may improve vascular health and reduce risk for cardiovascular events. This trial was registered at clinicaltrials.gov (NCT04385537).

Cerebrovascular impedance estimation with near-infrared and diffuse correlation spectroscopy.

Cerebrovascular impedance (CVI) is related to cerebral autoregulation (CA), which is the mechanism of the brain to maintain near-constant cerebral blood flow (CBF) despite changes in cerebral perfusion pressure (CPP). Changes in blood vessel impedance enable the stabilization of blood flow. Due to the interplay between CVI and CA, assessment of CVI may enable quantification of CA and may serve as a biomarker for cerebral health. We developed a method to quantify CVI based on a combination of diffuse correlation spectroscopy (DCS) and continuous wave (CW) near-infrared spectroscopy (NIRS). Data on healthy human volunteers were used to validate the method. A combined high-speed DCS-NIRS system was developed, allowing for simultaneous, noninvasive blood flow, and volume measurements in the same tissue compartment. Blood volume was used as a surrogate measurement for blood pressure and CVI was calculated as the spectral ratio of blood volume and blood flow changes. This technique was validated on six healthy human volunteers undergoing postural changes to elicit CVI changes. Averaged across the six subjects, a decrease in CVI was found for a head of bed (HOB) tilting of . These impedance changes were reversed when returning to the horizontal (0deg) HOB baseline. We developed a combined DCS-NIRS system, which measures CBF and volume changes, which we demonstrate can be used to measure CVI. Using CVI as a metric of CA may be beneficial for assessing cerebral health, especially in patients where CPP is altered.

Single Source-Detector Separation Approach to Calculate Tissue Oxygen Saturation Using Continuous Wave Near-Infrared Spectroscopy

Currently, common optical techniques to measure tissue oxygen saturation (StO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) include time domain (TD), frequency domain (FD), and continuous wave (CW) near-infrared spectroscopy (NIRS). While TD- and FD-NIRS can provide absolute hemoglobin concentration, these systems are often complex and expensive. CW-NIRS, such as diffuse reflectance spectroscopy and spatially resolved spectroscopy (SRS), are simpler and more affordable, but they still require at least two source-detector separations. Here, we propose a single source-detector separation (SSDS) approach to measure StO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> using reflected intensities from three wavelengths. The accuracy of the SSDS-based StO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> measurement was verified using an optical simulation and an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-vivo</i> experiment. Simulated spatially dependent reflectance was generated using the Virtual Tissue Simulator on a 1-layer model, which has StO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ranging from 0% to 100%. SSDS calculation yielded an equivalent StO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> to the actual value (average error = 0.3% ± 0.5%). We then performed StO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> measurements on seven healthy volunteers in the prefrontal cortex during a simulated hypercapnia test using a CW-NIRS device. This device consists of a light source and two photodetectors, which are 30 mm and 40 mm away from the light source. The cerebral oxygen saturation was calculated using both the SRS approach, which uses the reflected intensities at both separations, and the SSDS approach, which employs the reflected intensities at either 30 mm or 40 mm separation. The SRS-based StO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> calculation was similar to the value calculated from the SSDS method (average difference = 5.0% ± 1.1%). This proposed method will help to advance the development of miniaturized technologies to monitor StO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> continuously.

Load-Dependent Prefrontal Cortex Activation Assessed by Continuous-Wave Near-Infrared Spectroscopy during Two Executive Tasks with Three Cognitive Loads in Young Adults.

The present study examined the evolution of the behavioral performance, subjectively perceived difficulty, and hemodynamic activity of the prefrontal cortex as a function of cognitive load during two different cognitive tasks tapping executive functions. Additionally, it investigated the relationships between these behavioral, subjective, and neuroimaging data. Nineteen right-handed young adults (18-22 years) were scanned using continuous-wave functional near-infrared spectroscopy during the performance of n-back and random number generation tasks in three cognitive load conditions. Four emitter and four receptor optodes were fixed bilaterally over the ventrolateral and dorsolateral prefrontal cortices to record the hemodynamic changes. A self-reported scale measured the perceived difficulty. The findings of this study showed that an increasing cognitive load deteriorated the behavioral performance and increased the perceived difficulty. The hemodynamic activity increased parametrically for the three cognitive loads of the random number generation task and in a two-back and three-back compared to a one-back condition. In addition, the hemodynamic activity was specifically greater in the ventrolateral prefrontal cortex than in the dorsolateral prefrontal cortex for both cognitive tasks (random number generation and n-back tasks). Finally, the results highlighted some links between cerebral oxygenation and the behavioral performance, but not the subjectively perceived difficulty. Our results suggest that cognitive load affects the executive performance and perceived difficulty and that fNIRS can be used to specify the prefrontal cortex's implications for executive tasks involving inhibition and working memory updating.

Optical Monitoring of Breathing Patterns and Tissue Oxygenation: A Potential Application in COVID-19 Screening and Monitoring.

The worldwide outbreak of the novel Coronavirus (COVID-19) has highlighted the need for a screening and monitoring system for infectious respiratory diseases in the acute and chronic phase. The purpose of this study was to examine the feasibility of using a wearable near-infrared spectroscopy (NIRS) sensor to collect respiratory signals and distinguish between normal and simulated pathological breathing. Twenty-one healthy adults participated in an experiment that examined five separate breathing conditions. Respiratory signals were collected with a continuous-wave NIRS sensor (PortaLite, Artinis Medical Systems) affixed over the sternal manubrium. Following a three-minute baseline, participants began five minutes of imposed difficult breathing using a respiratory trainer. After a five minute recovery period, participants began five minutes of imposed rapid and shallow breathing. The study concluded with five additional minutes of regular breathing. NIRS signals were analyzed using a machine learning model to distinguish between normal and simulated pathological breathing. Three features: breathing interval, breathing depth, and O2Hb signal amplitude were extracted from the NIRS data and, when used together, resulted in a weighted average accuracy of 0.87. This study demonstrated that a wearable NIRS sensor can monitor respiratory patterns continuously and non-invasively and we identified three respiratory features that can distinguish between normal and simulated pathological breathing.

Quantifying tissue optical properties of human heads in vivo using continuous-wave near-infrared spectroscopy and subject-specific three-dimensional Monte Carlo models.

.Significance: Quantifying subject-specific optical properties (OPs) including absorption and transport scattering coefficients of tissues in the human head could improve the modeling of photon propagation for the analysis of functional near-infrared spectroscopy (fNIRS) data and dosage quantification in therapeutic applications. Current methods employ diffuse approximation, which excludes a low-scattering cerebrospinal fluid compartment and causes errors.Aim: This work aims to quantify OPs of the scalp, skull, and gray matter in vivo based on accurate Monte Carlo (MC) modeling.Approach: Iterative curve fitting was applied to quantify tissue OPs from multidistance continuous-wave NIR reflectance spectra. An artificial neural network (ANN) was trained using MC-simulated reflectance values based on subject-specific voxel-based tissue models to replace MC simulations as the forward model in curve fitting. To efficiently generate sufficient data for training the ANN, the efficiency of MC simulations was greatly improved by white MC simulations, increasing the detectors’ acceptance angle, and building a lookup table for interpolation.Results: The trained ANN was six orders of magnitude faster than the original MC simulations. OPs of the three tissue compartments were quantified from NIR reflectance spectra measured at the forehead of five healthy subjects and their uncertainties were estimated.Conclusions: This work demonstrated an MC-based iterative curve fitting method to quantify subject-specific tissue OPs in-vivo, with all OPs except for scattering coefficients of scalp within the ranges reported in the literature, which could aid the modeling of photon propagation in human heads.