Reliability of Near-Infrared Spectroscopy in People With Dark Skin Pigmentation

Sourcebook update: using near-infrared spectroscopy to assess skeletal muscle oxygen uptake

Monitoring the metabolic cost or oxygen consumption associated with rest and exercise is crucial to understanding the impact of disease or physical training on the health of individuals. Traditionally, measuring the skeletal muscle oxygen cost associated with exercise/muscle contractions can be rather expensive or invasive (i.e., muscle biopsies). More recently, specific protocols designed around the use of near-infrared spectroscopy (NIRS) have been shown to provide a quick, noninvasive easy-to-use tool to measure skeletal muscle oxygen consumption ([Formula: see text]). However, the data and results from NIRS devices are often misunderstood. Thus the primary purpose of this sourcebook update is to provide several experimental protocols students can utilize to improve their understanding of NIRS technology, learn how to analyze results from NIRS devices, and better understand how muscle contraction intensity and type (isometric, concentric, or eccentric) influence the oxygen cost of muscle contractions.NEW & NOTEWORTHY Compared to traditional methods, near-infrared spectroscopy (NIRS) provides a relatively cheap and easy-to-use noninvasive technique to measure skeletal muscle oxygen uptake following exercise. This laboratory not only enables students to learn about the basics of NIRS and muscle energetics but also addresses more complex questions regarding skeletal muscle physiology.

Continuous oxygen monitoring to enhance ex-vivo organ machine perfusion and reconstructive surgery

Continuous oxygenation monitoring of machine-perfused organs or transposed autologous tissue is not currently implemented in clinical practice. Oxygenation is a critical parameter that could be used to verify tissue viability and guide corrective interventions, such as perfusion machine parameters or surgical revision. This work presents an innovative technology based on oxygen-sensitive, phosphorescent metalloporphyrin allowing continuous and non-invasive oxygen monitoring of ex-vivo perfused vascularized fasciocutaneous flaps. The method comprises a small, low-energy optical transcutaneous oxygen sensor applied on the flap's skin paddle as well as oxygen sensing devices placed into the tubing. An intermittent perfusion setting was designed to study the response time and accuracy of this technology over a total of 54 perfusion cycles. We further evaluated correlation between the continuous oxygen measurements and gold-standard perfusion viability metrics such as vascular resistance, with good agreement suggesting potential to monitor graft viability at high frequency, opening the possibility to employ feedback control algorithms in the future. This proof-of-concept study opens a range of research and clinical applications in reconstructive surgery and transplantation at a time when perfusion machines undergo rapid clinical adoption with potential to improve outcomes across a variety of surgical procedures and dramatically increase access to transplant medicine.

Cross-modal plasticity in children with cochlear implant: converging evidence from EEG and functional near-infrared spectroscopy

Over the first years of life, the brain undergoes substantial organization in response to environmental stimulation. In a silent world, it may promote vision by (i) recruiting resources from the auditory cortex and (ii) making the visual cortex more efficient. It is unclear when such changes occur and how adaptive they are, questions that children with cochlear implants can help address. Here, we examined 7-18 years old children: 50 had cochlear implants, with delayed or age-appropriate language abilities, and 25 had typical hearing and language. High-density electroencephalography and functional near-infrared spectroscopy were used to evaluate cortical responses to a low-level visual task. Evidence for a 'weaker visual cortex response' and 'less synchronized or less inhibitory activity of auditory association areas' in the implanted children with language delays suggests that cross-modal reorganization can be maladaptive and does not necessarily strengthen the dominant visual sense.

Maximizing the Reliability and Precision of Measures of Prefrontal Cortical Oxygenation Using Frequency-Domain Near-Infrared Spectroscopy

Frequency-domain near-infrared spectroscopy (FD-NIRS) has been used for non-invasive assessment of cortical oxygenation since the late 1990s. However, there is limited research demonstrating clinical validity and general reproducibility. To address this limitation, recording duration for adequate validity and within- and between-day reproducibility of prefrontal cortical oxygenation was evaluated. To assess validity, a reverse analysis of 10-min-long measurements (n = 52) at different recording durations (1-10-min) was quantified via coefficients of variation and Bland-Altman plots. To assess within- and between-day within-subject reproducibility, participants (n = 15) completed 2-min measurements twice a day (morning/afternoon) for five consecutive days. While 1-min recordings demonstrated sufficient validity for the assessment of oxygen saturation (StO2) and total hemoglobin concentration (THb), recordings ≥4 min revealed greater clinical utility for oxy- (HbO) and deoxyhemoglobin (HHb) concentration. Females had lower StO2, THb, HbO, and HHb values than males, but variability was approximately equal between sexes. Intraclass correlation coefficients ranged from 0.50-0.96. The minimal detectable change for StO2 was 1.15% (95% CI: 0.336-1.96%) and 3.12 µM for THb (95% CI: 0.915-5.33 µM) for females and 2.75% (95%CI: 0.807-4.70%) for StO2 and 5.51 µM (95%CI: 1.62-9.42 µM) for THb in males. Overall, FD-NIRS demonstrated good levels of between-day reliability. These findings support the application of FD-NIRS in field-based settings and indicate a recording duration of 1 min allows for valid measures; however, data recordings of ≥4 min are recommended when feasible.

Neurodevelopmental Outcomes for Individuals With Congenital Heart Disease: Updates in Neuroprotection, Risk-Stratification, Evaluation, and Management: A Scientific Statement From the American Heart Association

Over the past decade, new research has advanced scientific knowledge of neurodevelopmental trajectories, factors that increase neurodevelopmental risk, and neuroprotective strategies for individuals with congenital heart disease. In addition, best practices for evaluation and management of developmental delays and disorders in this high-risk patient population have been formulated based on literature review and expert consensus. This American Heart Association scientific statement serves as an update to the 2012 statement on the evaluation and management of neurodevelopmental outcomes in children with congenital heart disease. It includes revised risk categories for developmental delay or disorder and an updated list of factors that increase neurodevelopmental risk in individuals with congenital heart disease according to current evidence, including genetic predisposition, fetal and perinatal factors, surgical and perioperative factors, socioeconomic disadvantage, and parental psychological distress. It also includes an updated algorithm for referral, evaluation, and management of individuals at high risk. Risk stratification of individuals with congenital heart disease with the updated categories and risk factors will identify a large and growing population of survivors at high risk for developmental delay or disorder and associated impacts across the life span. Critical next steps must include efforts to prevent and mitigate developmental delays and disorders. The goal of this scientific statement is to inform health care professionals caring for patients with congenital heart disease and other key stakeholders about the current state of knowledge of neurodevelopmental outcomes for individuals with congenital heart disease and best practices for neuroprotection, risk stratification, evaluation, and management.

From functional neuroimaging to neurostimulation: fNIRS devices as cognitive enhancers

Functional near-infrared spectroscopy (fNIRS) relies on near-infrared (NIR) light for changes in tissue oxygenation. For decades, this technique has been used in neuroscience to measure cortical activity. However, recent research suggests that NIR light directed to neural populations can modulate their activity through "photobiomodulation" (PBM). Yet, fNIRS is being used exclusively as a measurement tool. By adopting cognitive tests sensitive to prefrontal functioning, we show that a 'classical' fNIRS device, placed in correspondence of the prefrontal cortices of healthy participants, induces faster RTs and better accuracy in some of the indexes considered. A well-matched control group, wearing the same but inactive device, did not show any improvement. Hence, our findings indicate that the 'standard' use of fNIRS devices generates PBM impacting cognition. The neuromodulatory power intrinsic in that technique has been so far completely overlooked, and future studies will need to take this into account.

Second sensor to improve near-infrared spectroscopy flap monitor utility: A prospective study

OBJECTIVE

This study assesses whether use of continuous noninvasive near-infrared spectroscopy (NIRS) sensor on head and neck free flap (FF) with a second sensor on nonoperated tissue improves distinction between systemic hypoperfusion and FF compromise.

METHODS

Single-institution, prospective study of patients undergoing head and neck FF reconstruction from December 2018 to April 2020. FFs were continuously monitored using NIRS on a monitor paddle with a second (control) sensor on the shoulder. Crude StO2 and percent change in StO2 were compared between the FF and control sensors on each patient, and percent change and percent difference between the control and the monitor paddle were documented to assess for congruity. Sentinel events (e.g., hypotension and hematoma) were documented to assess the association with change in StO2. These events and timing of StO2 changes were noted to assess associations with change in StO2.

RESULTS

A total of 48 patients had complete data. Donor sites included 35 soft-tissue FFs and 13 fibula FFs. Average StO2 was 73.7 ± 5.5 for FFs and 71.4 ± 5.0 for control sensors. There were seven sentinel events during the study. At the time of the events, StO2 dropped significantly more for the FF than the control sensor (FF = 52.2% drop; control = 6.2% drop; p = .016). NIRS signal denoted change prior to changes in implantable arterial Doppler in all cases.

CONCLUSIONS

The addition of a second sensor when using NIRS as a primary modality for FF monitoring may improve distinction between FF compromise events and systemic hypoperfusion. By increasing accuracy of the monitor, there is a potential for decreased resident burden and decreased use of higher level of care nursing, which could reduce overall costs.

Whose Signals Are Being Amplified? Toward a More Equitable Clinical Psychophysiology

Research using psychophysiological methods holds great promise for refining clinical assessment, identifying risk factors, and informing treatment. Unfortunately, unique methodological features of existing approaches limit inclusive research participation and, consequently, generalizability. This brief overview and commentary provides a snapshot of the current state of representation in clinical psychophysiology, with a focus on the forms and consequences of ongoing exclusion of Black participants. We illustrate issues of inequity and exclusion that are unique to clinical psychophysiology, considering intersections among social constructions of Blackness and biased design of current technology used to measure electroencephalography, skin conductance, and other signals. We then highlight work by groups dedicated to quantifying and addressing these limitations. We discuss the need for reflection and input from a wider variety of stakeholders to develop and refine new technologies, given the risk of further widening disparities. Finally, we provide broad recommendations for clinical psychophysiology research.

Motor Processing in Children With Cochlear Implants as Assessed by Functional Near-Infrared Spectroscopy

Auditory-motor and visual-motor networks are often coupled in daily activities, such as when listening to music and dancing; but these networks are known to be highly malleable as a function of sensory input. Thus, congenital deafness may modify neural activities within the connections between the motor, auditory, and visual cortices. Here, we investigated whether the cortical responses of children with cochlear implants (CI) to a simple and repetitive motor task would differ from that of children with typical hearing (TH) and we sought to understand whether this response related to their language development. Participants were 75 school-aged children, including 50 with CI (with varying language abilities) and 25 controls with TH. We used functional near-infrared spectroscopy (fNIRS) to record cortical responses over the whole brain, as children squeezed the back triggers of a joystick that vibrated or not with the squeeze. Motor cortex activity was reflected by an increase in oxygenated hemoglobin concentration (HbO) and a decrease in deoxygenated hemoglobin concentration (HbR) in all children, irrespective of their hearing status. Unexpectedly, the visual cortex (supposedly an irrelevant region) was deactivated in this task, particularly for children with CI who had good language skills when compared to those with CI who had language delays. Presence or absence of vibrotactile feedback made no difference in cortical activation. These findings support the potential of fNIRS to examine cognitive functions related to language in children with CI.

Measurements of Electrodermal Activity, Tissue Oxygen Saturation, and Visual Analog Scale for Different Cuff Pressures

The quantification of comfort in binding parts, essential human-machine interfaces (HMI) for the functioning of rehabilitation robots, is necessary to reduce physical strain on the user despite great achievements in their structure and control. This study aims to investigate the physiological impacts of binding parts by measuring electrodermal activity (EDA) and tissue oxygen saturation (StO2). In Experiment 1, EDA was measured from 13 healthy subjects under three different pressure conditions (10, 20, and 30 kPa) for 1 min using a pneumatic cuff on the right thigh. In Experiment 2, EDA and StO2 were measured from 10 healthy subjects for 5 min. To analyze the correlation between EDA parameters and the decrease in StO2, a survey using the visual analog scale (VAS) was conducted to assess the level of discomfort at each pressure. The EDA signal was decomposed into phasic and tonic components, and the EDA parameters were extracted from these two components. RM ANOVA and a post hoc paired t-test were used to determine significant differences in parameters as the pressure increased. The results showed that EDA parameters and the decrease in StO2 significantly increased with the pressure increase. Among the extracted parameters, the decrease in StO2 and the mean SCL proved to be effective indicators. Such analysis outcomes would be highly beneficial for studies focusing on the comfort assessment of the binding parts of rehabilitation robots.

Evaluation of stroke volume estimation during orthostatic stress: the utility of Modelflow

Advanced blood pressure monitoring devices contain algorithms that permit estimation of stroke volume (SV). Modelflow (Finapres Medical Systems) is one common method to non-invasively estimate beat-to-beat SV. However, Modelflow accuracy during profound reductions in SV is unclear. We aimed to compare SV estimation by Modelflow and echocardiography, at rest and during orthostatic challenge. We tested 13 individuals (age 24 ± 2 years; 7 female) using combined head-up tilt and graded lower body negative pressure, continued until presyncope. SV was derived by both Modelflow and echocardiography on multiple occasions while supine, during orthostatic stress, and at presyncope. SV index (SVI) was determined by normalising SV for body surface area. Bias and limits of agreement were determined using Bland-Altman analyses. Two one-sided tests (TOST) examined equivalency. Across all timepoints, Modelflow estimates of SV (73.2 ± 1.6 ml) were strongly correlated with echocardiography estimates (66.1 ± 1.3 ml) (r = 0.56, P  < 0.001) with a bias of +7.1 ± 21.1 ml. Bias across all timepoints was further improved when SV was indexed (+3.6 ± 12.0 ml.m -2 ). Likewise, when assessing responses relative to baseline, Modelflow estimates of SV (-23.4 ± 1.4%) were strongly correlated with echocardiography estimates (-19.2 ± 1.3%) (r = 0.76, P  < 0.001), with minimal bias (-4.2 ± 13.1%). TOST testing revealed equivalency to within 15% of the clinical standard for SV and SVI, both expressed as absolute values and relative to baseline. Modelflow can be used to track changes in SV during profound orthostatic stress, with accuracy enhanced with correction relative to baseline values or body size. These data support the use of Modelflow estimates of SV for autonomic function testing.

Going beyond the means: Exploring the role of bias from digital determinants of health in technologies

BACKGROUND

In light of recent retrospective studies revealing evidence of disparities in access to medical technology and of bias in measurements, this narrative review assesses digital determinants of health (DDoH) in both technologies and medical formulae that demonstrate either evidence of bias or suboptimal performance, identifies potential mechanisms behind such bias, and proposes potential methods or avenues that can guide future efforts to address these disparities.

APPROACH

Mechanisms are broadly grouped into physical and biological biases (e.g., pulse oximetry, non-contact infrared thermometry [NCIT]), interaction of human factors and cultural practices (e.g., electroencephalography [EEG]), and interpretation bias (e.g, pulmonary function tests [PFT], optical coherence tomography [OCT], and Humphrey visual field [HVF] testing). This review scope specifically excludes technologies incorporating artificial intelligence and machine learning. For each technology, we identify both clinical and research recommendations.

CONCLUSIONS

Many of the DDoH mechanisms encountered in medical technologies and formulae result in lower accuracy or lower validity when applied to patients outside the initial scope of development or validation. Our clinical recommendations caution clinical users in completely trusting result validity and suggest correlating with other measurement modalities robust to the DDoH mechanism (e.g., arterial blood gas for pulse oximetry, core temperatures for NCIT). Our research recommendations suggest not only increasing diversity in development and validation, but also awareness in the modalities of diversity required (e.g., skin pigmentation for pulse oximetry but skin pigmentation and sex/hormonal variation for NCIT). By increasing diversity that better reflects patients in all scenarios of use, we can mitigate DDoH mechanisms and increase trust and validity in clinical practice and research.

Performance of Near-Infrared Spectroscopy in Detecting Acute Tourniquet-Induced Upper-Extremity Ischemia Across Different Skin Phenotypes

PURPOSE

Diagnosing acute tissue ischemia is challenging, particularly in patients with higher skin melanin content. We investigated whether near-infrared spectroscopy (NIRS) is effective and consistent in detecting upper extremity ischemia across various skin phenotypes.

METHODS

Volunteers underwent tourniquet-induced upper extremity ischemia. Skin color was evaluated by the Fitzpatrick scale (FP, range: I-VI) and the Von Luschan scale (vL, range: 1-36). A NIRS probe was placed on one finger. The tourniquet was inflated to 250 mmHg and perfusion was restricted for 7 minutes, followed by a 10-minute monitored reperfusion period. The percent tissue oxygenation (StO₂) was recorded.

RESULTS

A total of 55 volunteers were enrolled (22 self-identified as Caucasian, 21 African American, 7 Asian, 2 Latinx, and 2 Biracial). Average starting and ending StO₂ for the cohort was 72.2% and 45.9%, respectively. However, there was variability based on skin melanin content. Increasing vL correlated with lower starting StO₂, smaller StO₂ decrease, and shorter time to reach ischemic steady state. High skin melanin (FP scale IV-VI) was associated with significantly lower starting StO₂ (-7.1%) and shorter time to reach ischemic steady state (-0.3 mins). African Americans had lower starting StO₂ (-8.6%) and 7.8% lesser total StO₂ decrease than other groups.

CONCLUSIONS

NIRS can rapidly detect acute onset tissue ischemia in the upper extremity. However, given the lower starting StO₂ and smaller total StO₂ decrease after tourniquet-induced ischemia for patients with higher skin melanin, using NIRS for clinical detection of acute ischemia may be more challenging in these patients. These inconsistencies may limit use of NIRS clinically for spot identification of ischemia.

CLINICAL RELEVANCE

Although NIRS has utility in tracking tissue oxygenation, variable performance with different skin melanin content raises concerns as to whether different cutoff/threshold levels are needed for different groups, and whether NIRS is reliable for spot checks in acute events.

Scaling of Algorithmic Bias in Pulse Oximetry with Signal-to-Noise Ratio

Recent work has noted a skin-color bias in existing pulse oximetry systems in their estimation of arterial oxygen saturation. Frequently, the algorithm used by these systems estimate a "ratio-of-ratios", called the "R-value", on their way to estimating the oxygen saturation. In this work, we focus on an "SNR-related" bias that is due to noise in measurements. We derive expressions for the SNR-related bias in R-value estimation, and observe how it scales with the signal-to-noise ratio (SNR). We show that the bias can arise at two steps of R-value estimation: in estimating the max and min of a pulsatile signal, and, additionally in taking ratios to estimate the R-value. We assess the bias resulting from the combination of the two steps, but also separate out contributions of each step. By doing so, we deduce that the bias induced in max and min estimation is likely to dominate. Because the SNR tends to get worse with higher melanin concentration, our result provides a sense of scaling of this bias with melanin concentration.

Brightening the Study of Listening Effort with Functional Near-Infrared Spectroscopy: A Scoping Review

Listening effort is a long-standing area of interest in auditory cognitive neuroscience. Prior research has used multiple techniques to shed light on the neurophysiological mechanisms underlying listening during challenging conditions. Functional near-infrared spectroscopy (fNIRS) is growing in popularity as a tool for cognitive neuroscience research, and its recent advances offer many potential advantages over other neuroimaging modalities for research related to listening effort. This review introduces the basic science of fNIRS and its uses for auditory cognitive neuroscience. We also discuss its application in recently published studies on listening effort and consider future opportunities for studying effortful listening with fNIRS. After reading this article, the learner will know how fNIRS works and summarize its uses for listening effort research. The learner will also be able to apply this knowledge toward generation of future research in this area.

Using preregistration as a tool for transparent fNIRS study design

Significance

The expansion of functional near-infrared spectroscopy (fNIRS) methodology and analysis tools gives rise to various design and analytical decisions that researchers have to make. Several recent efforts have developed guidelines for preprocessing, analyzing, and reporting practices. For the planning stage of fNIRS studies, similar guidance is desirable. Study preregistration helps researchers to transparently document study protocols before conducting the study, including materials, methods, and analyses, and thus, others to verify, understand, and reproduce a study. Preregistration can thus serve as a useful tool for transparent, careful, and comprehensive fNIRS study design.

Aim

We aim to create a guide on the design and analysis steps involved in fNIRS studies and to provide a preregistration template specified for fNIRS studies.

Approach

The presented preregistration guide has a strong focus on fNIRS specific requirements, and the associated template provides examples based on continuous-wave (CW) fNIRS studies conducted in humans. These can, however, be extended to other types of fNIRS studies.

Results

On a step-by-step basis, we walk the fNIRS user through key methodological and analysis-related aspects central to a comprehensive fNIRS study design. These include items specific to the design of CW, task-based fNIRS studies, but also sections that are of general importance, including an in-depth elaboration on sample size planning.

Conclusions

Our guide introduces these open science tools to the fNIRS community, providing researchers with an overview of key design aspects and specification recommendations for comprehensive study planning. As such it can be used as a template to preregister fNIRS studies or merely as a tool for transparent fNIRS study design.

Neuromonitoring in Critically Ill Patients

OBJECTIVES

Critically ill patients are at high risk of acute brain injury. Bedside multimodality neuromonitoring techniques can provide a direct assessment of physiologic interactions between systemic derangements and intracranial processes and offer the potential for early detection of neurologic deterioration before clinically manifest signs occur. Neuromonitoring provides measurable parameters of new or evolving brain injury that can be used as a target for investigating various therapeutic interventions, monitoring treatment responses, and testing clinical paradigms that could reduce secondary brain injury and improve clinical outcomes. Further investigations may also reveal neuromonitoring markers that can assist in neuroprognostication. We provide an up-to-date summary of clinical applications, risks, benefits, and challenges of various invasive and noninvasive neuromonitoring modalities.

DATA SOURCES

English articles were retrieved using pertinent search terms related to invasive and noninvasive neuromonitoring techniques in PubMed and CINAHL.

STUDY SELECTION

Original research, review articles, commentaries, and guidelines.

DATA EXTRACTION

Syntheses of data retrieved from relevant publications are summarized into a narrative review.

DATA SYNTHESIS

A cascade of cerebral and systemic pathophysiological processes can compound neuronal damage in critically ill patients. Numerous neuromonitoring modalities and their clinical applications have been investigated in critically ill patients that monitor a range of neurologic physiologic processes, including clinical neurologic assessments, electrophysiology tests, cerebral blood flow, substrate delivery, substrate utilization, and cellular metabolism. Most studies in neuromonitoring have focused on traumatic brain injury, with a paucity of data on other clinical types of acute brain injury. We provide a concise summary of the most commonly used invasive and noninvasive neuromonitoring techniques, their associated risks, their bedside clinical application, and the implications of common findings to guide evaluation and management of critically ill patients.

CONCLUSIONS

Neuromonitoring techniques provide an essential tool to facilitate early detection and treatment of acute brain injury in critical care. Awareness of the nuances of their use and clinical applications can empower the intensive care team with tools to potentially reduce the burden of neurologic morbidity in critically ill patients.

Utilizing Near-Infrared Spectroscopy to Identify Pediatric Trauma Patients Needing Lifesaving Interventions: A Prospective Study

OBJECTIVES

The aim of this study was to prospectively investigate the role of near-infrared spectroscopy (NIRS) in identifying pediatric trauma patients who required lifesaving interventions (LSIs).

METHODS

Prospective cohort study of children age 0 to 18 years who activated the trauma team response between August 15, 2017, and February 12, 2019, at a large, urban pediatric emergency department (ED).The relationship between the lowest somatic NIRS saturation and the need for LSIs (based on published consensus definition) was investigated. Categorical variables were analyzed by χ 2 test, and continuous variables were analyzed by Student t test.

RESULTS

A total of 148 pediatric trauma patients had somatic NIRS monitoring and met the inclusion criteria. Overall, 65.5% were male with a mean ± SD age of 10.9 ± 6.0 years. Injuries included 67.6% blunt trauma and 28.4% penetrating trauma with mortality of 3.4% (n = 5). Overall, the median lowest somatic NIRS value was 72% (interquartile range, 58%-88%; range, 15%-95%), and 43.9% of patients had a somatic NIRS value <70%. The median somatic NIRS duration recorded was 11 minutes (interquartile range, 7-17 minutes; range, 1-105 minutes). Overall, 36.5% of patients required a LSI including 53 who required a lifesaving procedure, 17 required blood products, and 17 required vasopressors. Among procedures, requiring a thoracostomy was significant.Pediatric trauma patients with a somatic NIRS value <70% had a significantly increased odds of requiring a LSI (odds ratio, 2.11; 95% confidence interval, 1.07-4.20). Somatic NIRS values <70% had a sensitivity and specificity of 56% and 63%, respectively.

CONCLUSIONS

Pediatric trauma patients with somatic NIRS values <70% within 30 minutes of ED arrival have an increased odds of requiring LSIs. Among LSIs, pediatric trauma patients requiring thoracostomy was significant. The role of NIRS in incrementally improving the identification of critically injured children in the ED and prehospital setting should be evaluated in larger prospective multicenter studies.

Observation of Tissue Oxygenation Changes Using Remote Photoplesysmography with a Smartphone

BACKGROUND

Tissue oxygenation is a critical marker of tissue status and can be used to evaluate and track wound progress, the viability of transplanted tissue, and burns. Thus, the determination of tissue oxygenation (preferably remotely) is of great importance.

AIM

Explore the impact of oxygenation changes on tissue color.

MATERIAL AND METHODS

The rPPG of both hands was acquired using a stand-mounted smartphone (iPhone 8) placed about 10 cm above the hands. A 60 s baseline was followed by occlusion of one arm using a cuff inflated to 200 mmHg for approximately 2 min. The cuff was then rapidly deflated, followed by a 60 s recovery period. The reference muscle oxygenation signal (SmO2) was acquired using the near-infrared contact Moxy device (Fortiori Design LLC) placed on the forearm distal to the occlusion. The data were collected on both hands of 28 healthy volunteers.

RESULTS

rPPG can observe changes in tissue oxygenation, which was confirmed across 28 participants using a robust reference standard.

CONCLUSION

We have an initial confirmation of the notion that rPPG can monitor changes in tissue oxygenation. However, a spectrum of rPPG and SmO2 reductions is observed, which should be explored in future work.

Percutaneously introduced wireless intramuscular near-infrared spectroscopy device detects muscle oxygenation changes in porcine model of lower extremity compartment syndrome

Serial examination and direct measurement of intracompartmental pressure (ICP) are suboptimal strategies for the detection of acute compartment syndrome (CS) because they are operator-dependent and yield information that only indirectly reflects intracompartmental muscle perfusion. As a result, instances of unnecessary fasciotomy and unrecognized CS are relatively common. Recently, near-infrared spectroscopy (NIRS)-based systems for compartment monitoring have generated interest as an adjunct tool. Under ideal conditions, NIRS directly measures the oxygenation of intracompartmental muscle (StO₂ ), thereby obviating the challenges of interpreting equivocal clinical examination or ICP data. Despite these potential advantages, existing NIRS sensors are plagued by technical difficulties that limit clinical utility. Most of these limitations relate to their transcutaneous design that makes them susceptible to both interference from intervening skin/subcutaneous tissue, underlying hematoma, and instability of the skin-sensor interface. Here, we present a flexible, wireless, Bluetooth-enabled, percutaneously introducible intramuscular NIRS device that directly and continuously measures the StO₂ of intracompartmental muscle. Proof of concept for this device is demonstrated in a swine lower extremity balloon compression model of acute CS, wherein we simultaneously track muscle oxygenation, ICP, and compartment perfusion pressure (PP). The observed StO₂ decreased with increasing ICP and decreasing PP and then recovered following pressure reduction. The mean change in StO₂ as the PP was decreased from baseline to 30 mmHg was -7.6%. The mean difference between baseline and nadir StO₂ was -17.4%. Cross-correlations (absolute value) describing the correspondence between StO₂ and ICP were >0.73. This novel intramuscular NIRS device identifies decreased muscle perfusion in the setting of evolving CS.

Inspiratory and leg muscle blood flows during inspiratory muscle metaboreflex activation in heart failure with preserved ejection fraction

The purpose of this study was to determine the cardiovascular consequences elicited by activation of the inspiratory muscle metaboreflex in patients with heart failure with preserved ejection fraction (HFpEF) and controls. Patients with HFpEF (n = 15; 69 ± 10 yr; 33 ± 4 kg/m2) and controls (n = 14; 70 ± 8 yr; 28 ± 4 kg/m2) performed an inspiratory loading trial at 60% maximal inspiratory pressure (PIMAX) until task failure. Mean arterial pressure (MAP) was measured continuously. Near-infrared spectroscopy and bolus injections of indocyanine green dye were used to determine the percent change in blood flow index (%ΔBFI) from baseline to the final minute of inspiratory loading in the vastus lateralis and sternocleidomastoid muscles. Vascular resistance index (VRI) was calculated. Time to task failure was shorter in HFpEF than in controls (339 ± 197 s vs. 626 ± 403 s; P = 0.02). Compared with controls, patients with HFpEF had a greater increase from baseline in MAP (16 ± 7 vs. 10 ± 6 mmHg) and vastus lateralis VRI (76 ± 45 vs. 32 ± 19%) as well as a greater decrease in vastus lateralis %ΔBFI (-32 ± 14 vs. -17 ± 9%) (all, P < 0.05). Sternocleidomastoid %ΔBFI normalized to absolute inspiratory pressure was higher in HFpEF compared with controls (8.0 ± 5.0 vs. 4.0 ± 1.9% per cmH2O·s; P = 0.03). These data indicate that patients with HFpEF exhibit exaggerated cardiovascular responses with inspiratory muscle metaboreflex activation compared with controls.NEW & NOTEWORTHY Respiratory muscle dysfunction is thought to contribute to exercise intolerance in heart failure with preserved ejection fraction (HFpEF); however, the underlying mechanisms are unknown. In the present study, patients with HFpEF had greater increases in leg muscle vascular resistance index and greater decreases in leg muscle blood flow index compared with controls during inspiratory resistive breathing (to activate the metaboreflex). Furthermore, respiratory muscle blood flow index responses normalized to pressure generation during inspiratory resistive breathing were exaggerated in HFpEF compared with controls.

Quantitative Luminescence Photography of a Swellable Hydrogel Dressing with a Traffic-Light Response to Oxygen

Sensor-integrated wound dressings are emerging tools applicable to a wide variety of medical applications from emergency triage to at-home monitoring. Uncomfortable, unnecessary wound dressing changes may be avoided by providing quantitative insight into tissue characteristics related to wound healing such as tissue oxygenation, pH, and exudate/transudate volume. Here, a simple cost-effective methodology for quantifying oxygen and pH in a swellable hydrogel dressing using a single photograph is presented. The red and green luminescence of a novel dendritic polyamine Pt-porphyrin and fluorescein conjugate quantitatively responds to oxygen and pH, respectively, and enables robust sensing. The porphyrin conjugate, when combined with a four-arm star polyethylene glycol (PEG) amine polymer, rapidly crosslinks at room temperature with an N-hydroxysuccinimide (NHS)-PEG crosslinker to form a color-changing hydrogel dressing with tunable swelling capabilities applicable to a variety of wound environments. An inexpensive digital single-lens reflex (DSLR) camera modified with bandpass filters captures the hydrogel luminescence using simple macroscopic photography, and conversion to HSB colorspace allows for intensity-independent image analysis of the hydrogels' dual modality response. The hydrogel formulation exhibits a robust and validated visible red-orange-green "traffic light" spectrum in response to oxygen changes, regardless of swelling state, pH, or autofluorescence from skin, thereby enabling the clinician friendly naked-eye feedback.

Skin Pigmentation Influence on Pulse Oximetry Accuracy: A Systematic Review and Bibliometric Analysis

Nowadays, pulse oximetry has become the standard in primary and intensive care units, especially as a triage tool during the current COVID-19 pandemic. Hence, a deeper understanding of the measurement errors that can affect precise readings is a key element in clinical decision-making. Several factors may influence the accuracy of pulse oximetry, such as skin color, body temperature, altitude, or patient movement. The skin pigmentation effect on pulse oximetry accuracy has long been studied reporting some contradictory conclusions. Recent studies have shown a positive bias in oxygen saturation measurements in patients with darkly pigmented skin, particularly under low saturation conditions. This review aims to study the literature that assesses the influence of skin pigmentation on the accuracy of these devices. We employed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement to conduct a systematic review retrospectively since February 2022 using WOS, PubMed, and Scopus databases. We found 99 unique references, of which only 41 satisfied the established inclusion criteria. A bibliometric and scientometrics approach was performed to examine the outcomes of an exhaustive survey of the thematic content and trending topics.

Could Near Infrared Spectroscopy (NIRS) be the new weapon in our fight against Necrotising Enterocolitis?

There is no ideal single gut tissue or inflammatory biomarker available to help to try and identify Necrotising Enterocolitis (NEC) before its clinical onset. Neonatologists are all too familiar with the devastating consequences of NEC, and despite many advances in neonatal care the mortality and morbidity associated with NEC remains significant. In this article we review Near Infrared Spectroscopy (NIRS) as a method of measuring regional gut tissue oxygenation. We discuss its current and potential future applications, including considering its effectiveness as a possible new weapon in the early identification of NEC.

Products for Monitoring Glucose Levels in the Human Body With Noninvasive Optical, Noninvasive Fluid Sampling, or Minimally Invasive Technologies

BACKGROUND

Conventional home blood glucose measurements require a sample of blood that is obtained by puncturing the skin at the fingertip. To avoid the pain associated with this procedure, there is high demand for medical products that allow glucose monitoring without blood sampling. In this review article, all such products are presented.

METHODS

In order to identify such products, four different sources were used: (1) PubMed, (2) Google Patents, (3) Diabetes Technology Meeting Startup Showcase participants, and (4) experts in the field of glucose monitoring. The information obtained were filtered by using two inclusion criteria: (1) regulatory clearance, and/or (2) significant coverage in Google News starting in the year 2016, unless the article indicated that the product had been discontinued. The identified bloodless monitoring products were classified into three categories: (1) noninvasive optical, (2) noninvasive fluid sampling, and (3) minimally invasive devices.

RESULTS

In total, 28 noninvasive optical, 6 noninvasive fluid sampling, and 31 minimally invasive glucose monitoring products were identified. Subsequently, these products were characterized according to their regulatory, technological, and consumer features. Products with regulatory clearance are described in greater detail according to their advantages and disadvantages, and with design images.

CONCLUSIONS

Based on favorable technological features, consumer features, and other advantages, several bloodless products are commercially available and promise to enhance diabetes management. Paths for future products are discussed with an emphasis on understanding existing barriers related to both technical and non-technical issues.

Utilizing Near-Infrared Spectroscopy (NIRS) to Identify Pediatric Trauma Patients Needing Lifesaving Interventions (LSIs): A Retrospective Study

OBJECTIVES

The aim of this study was to investigate the role of near-infrared spectroscopy (NIRS) in identifying pediatric trauma patients who required lifesaving interventions (LSIs).

METHODS

Retrospective chart review of children age 0 to 18 years who activated the trauma team response between January 1, 2015 and August 14, 2017, at a large, urban pediatric emergency department. The lowest somatic NIRS saturation and the need for LSIs (based on published consensus definition) were abstracted from the chart. χ2 and descriptive statistics were used for analysis.

RESULTS

The charts of 84 pediatric trauma patients were reviewed. Overall, 80% were boys with a mean age of 10.4 years (SD, 6.2 years). Injuries included 56% blunt trauma and 36% penetrating trauma with mortality of 10.7% (n = 9). Overall, the median lowest NIRS value was 67% (interquartile range, 51-80%; range, 15%-95%) and 54.8% of the patients had a NIRS value less than 70%. The median somatic NIRS duration recorded was 12 minutes (interquartile range, 6-17 minutes; range, 1-59 minutes). Overall, 50% of patients required a LSI, including 39 who required a lifesaving procedure, 11 required blood products, and 14 required vasopressors. Pediatric trauma patients with NIRS less than 70% had a significantly increased odds of requiring a LSI (odds ratio, 2.67; 95% confidence interval, 1.10-6.47). NIRS less than 70% had a sensitivity and specificity of 67% and 57% respectively.

CONCLUSIONS

Pediatric trauma patients with somatic NIRS less than 70% within 30 minutes of emergency department arrival are associated with the need for LSIs. Continuous NIRS monitoring in the pediatric trauma population should be evaluated prospectively.

Cerebral oximetry: a developing tool for monitoring cerebral oxygenation during cardiopulmonary resuscitation

Despite improvements in cardiopulmonary resuscitation (CPR), survival and neurologic recovery after cardiac arrest remain very poor because of the impact of severe ischemia and subsequent reperfusion injury. As the likelihood of survival and favorable neurologic outcome decreases with increasing severity of ischemia during CPR, developing methods to measure the magnitude of ischemia during resuscitation, particularly cerebral ischemia, is critical for improving overall outcomes. Cerebral oximetry, which measures regional cerebral oxygen saturation (rSO₂ ) by near-infrared spectroscopy, has emerged as a potentially beneficial marker of cerebral ischemia during CPR. In numerous preclinical and clinical studies, higher rSO₂ during CPR has been associated with improved cardiac arrest survival and neurologic outcome. In this narrative review, we summarize the scientific rationale and validation of cerebral oximetry across populations and pathophysiologic states, discuss the evidence surrounding its use to predict return of spontaneous circulation, rearrest, and neurologic outcome, and provide suggestions for incorporation of cerebral oximetry into CPR practice.

Assessment of cerebral oxygenation response to hemodialysis using near-infrared spectroscopy (NIRS): Challenges and solutions

To date, the clinical use of functional near-infrared spectroscopy (NIRS) to detect cerebral ischemia has been largely limited to surgical settings, where motion artifacts are minimal. In this study, we present novel techniques to address the challenges of using NIRS to monitor ambulatory patients with kidney disease during approximately eight hours of hemodialysis (HD) treatment. People with end-stage kidney disease who require HD are at higher risk for cognitive impairment and dementia than age-matched controls. Recent studies have suggested that HD-related declines in cerebral blood flow might explain some of the adverse outcomes of HD treatment. However, there are currently no established paradigms for monitoring cerebral perfusion in real-time during HD treatment. In this study, we used NIRS to assess cerebral hemodynamic responses among 95 prevalent HD patients during two consecutive HD treatments. We observed substantial signal attenuation in our predominantly Black patient cohort that required probe modifications. We also observed consistent motion artifacts that we addressed by developing a novel NIRS methodology, called the HD cerebral oxygen demand algorithm (HD-CODA), to identify episodes when cerebral oxygen demand might be outpacing supply during HD treatment. We then examined the association between a summary measure of time spent in cerebral deoxygenation, derived using the HD-CODA, and hemodynamic and treatment-related variables. We found that this summary measure was associated with intradialytic mean arterial pressure, heart rate, and volume removal. Future studies should use the HD-CODA to implement studies of real-time NIRS monitoring for incident dialysis patients, over longer time frames, and in other dialysis modalities.

Measurement of Tissue Oximetry in Standing Unsedated and Sedated Horses

Near infrared spectroscopy (NIRS) noninvasively measures peripheral tissue oxygen saturation (StO₂) and may be useful to detect early changes in StO₂ in anaesthetized and critically ill horses. This study aimed to identify the muscle belly that provided the highest percentage of successful StO₂ readings and the highest mean StO₂ value. Fifty adult horses were enrolled in a prospective controlled study. StO₂ was measured at six different muscles in each horse, for each intervention: hair overlying the muscle was clipped (post clipping: PC), clipped skin was cleaned with chlorhexidine (post-surgical prepping: PP) and medetomidine was administered intravenously (post medetomidine: PM). Mean StO₂ values were calculated for each muscle, and a linear effects model was used to assess the effect of muscle group and intervention on StO₂. The sartorius muscle gave the highest percentage of successful StO₂ values (p < 0.001) and the highest mean (90% CI) StO₂ values for the PC, PP and PM interventions. Surgical prepping of the skin increased the success for measurement of StO₂ values. For all muscles, administration of medetomidine was associated with lower StO₂ values (p < 0.001). In conclusion, of the muscles examined, the sartorius muscle may be the preferred muscle to measure StO₂ in horses, and clipping and cleaning of the probe placement site is recommended.

Muscle mitochondrial capacity in high- and low-fitness females using near-infrared spectroscopy

The recovery of muscle oxygen consumption (m V ˙ O₂ ) after exercise measured using near-infrared spectroscopy (NIRS) provides a measure of skeletal muscle mitochondrial capacity. Nevertheless, due to sex differences in factors that can influence scattering and thus penetration depth of the NIRS signal in the tissue, e.g., subcutaneous adipose tissue thickness and intramuscular myoglobin and hemoglobin, it is unknown whether results in males can be extrapolated to a female population. Therefore, the aim of this study was to measure skeletal muscle mitochondrial capacity in females at different levels of aerobic fitness to test whether NIRS can measure relevant differences in mitochondrial capacity. Mitochondrial capacity was analyzed in the gastrocnemius muscle and the wrist flexors of 32 young female adults, equally divided in relatively high ( V ˙ O₂ peak ≥ 47 ml/kg/min) and relatively low aerobic fitness group ( V ˙ O₂ peak ≤ 37 ml/kg/min). m V ˙ O₂ recovery was significantly faster in the high- compared to the low-fitness group in the gastrocnemius, but not in the wrist flexors (p = 0.009 and p = 0.0528, respectively). Furthermore, V ˙ O₂ peak was significantly correlated to m V ˙ O₂ recovery in both gastrocnemius (R²  = 0.27, p = 0.0051) and wrist flexors (R²  = 0.13, p = 0.0393). In conclusion, NIRS measurements can be used to assess differences in mitochondrial capacity within a female population and is correlated to V ˙ O₂ peak. This further supports NIRS assessment of muscle mitochondrial capacity providing additional evidence for NIRS as a promising approach to monitor mitochondrial capacity, also in an exclusively female population.

Changes in Muscle Oxygen Saturation Measured Using Wireless Near-Infrared Spectroscopy in Resistance Training: A Systematic Review

Background: This study aimed to report, through a systematic review of the literature, the baseline and final reference values obtained by near-infrared spectroscopy (NIRS) of muscle oxygen saturation (SmO₂) during resistance training in healthy adults. Methods: Original research studies were searched from four databases (Scopus, PubMed, WOS, and SportDiscus). Subsequently, three independent reviewers screened the titles and abstracts, followed by full-text reviews to assess the studies’ eligibility. Results: Four studies met the inclusion criteria, data were extracted and methodological quality was assessed using the Downs and Black scale. Muscle oxygen saturation (% SmO2) during reported muscle strength exercises showed a decreasing trend after a muscle strength protocol; that is, before the protocol (range = 68.07–77.9%) and after (range = 9.50–46.09%). Conclusions: The trend of the SmO₂ variables is to decrease after a muscle strength protocol. Studies are lacking that allow expanding the use of these devices during this type of training.

The impact of vatinoxan on medetomidine-ketamine-midazolam immobilization in Patagonian maras (Dolichotis patagonum)

OBJECTIVE

To compare cardiovascular and ventilatory effects, immobilization quality and effects on tissue perfusion of a medetomidine-ketamine-midazolam combination with or without vatinoxan (MK-467), a peripherally acting α₂-adrenoceptor antagonist.

STUDY DESIGN

Randomized, blinded, crossover study.

ANIMALS

A group of nine healthy Patagonian maras (Dolichotis patagonum).

METHODS

Maras were immobilized twice with: 1) medetomidine hydrochloride (0.1 mg kg^-1) + ketamine (5 mg kg^-1) + midazolam (0.1 mg kg^-1) (MKM) + saline or 2) MKM + vatinoxan hydrochloride (0.8 mg kg^-1), administered intramuscularly. Drugs were mixed in the same syringe. At 20, 30 and 40 minutes after injection, invasive blood pressure, heart rate, respiration rate, end-tidal CO₂, haemoglobin oxygen saturation, and muscle oxygenation were measured, arteriovenous oxygen content difference was calculated. Muscle tone, jaw tone, spontaneous blinking and palpebral reflex were evaluated. Times to initial effect, recumbency, initial arousal and control of the head were recorded. Paired t test, Wilcoxon matched-pairs signed rank test and analysis of variance were used to compare protocols; (p < 0.05).

RESULTS

Vatinoxan significantly reduced systolic (p = 0.0002), mean (MAP; p < 0.0001) and diastolic (p < 0.0001) arterial blood pressures between 20 and 40 minutes. MAPs at 30 minutes (mean ± standard deviation) with MKM and MKM + vatinoxan were 105 ± 12 and 71 ± 14 mmHg, respectively. Without vatinoxan, four animals were hypertensive (MAP > 120 mmHg), whereas with vatinoxan, four animals were hypotensive (MAP < 60 mmHg). Muscle and jaw tone were significantly more frequently present with MKM (both p = 0.039). Other measurements did not significantly differ between protocols.

CONCLUSIONS AND CLINICAL RELEVANCE

In Patagonian maras, vatinoxan attenuated the increase in blood pressure induced by medetomidine. Muscle and jaw tone were more frequently present with MKM, indicating that quality of immobilization with vatinoxan was more profound.

Circumferential tissue compression at the lower limb during walking, and its effect on discomfort, pain and tissue oxygenation: Application to soft exoskeleton design

Soft exoskeletons apply compressive forces at the limbs via connection cuffs to actuate movement or stabilise joints. To avoid excessive mechanical loading, the interface with the wearer's body needs to be carefully designed. The purpose of this study was to establish the magnitude of circumferential compression at the lower limb during walking that causes discomfort/pain. It was hypothesized that the thresholds differ from those during standing. A cohort of 21 healthy participants were tested using two sizes of pneumatic cuffs, inflated at the thigh and calf in a tonic or phasic manner. The results showed lower inflation pressures triggering discomfort/pain at the thigh, with tonic compression, and wider pneumatic cuffs. The thresholds were lower during walking than standing still. Deep tissue oxygenation increased during phasic compression and decreased during tonic compression. According to the findings, circumferential compression by soft exoskeletons is preferably applied at anatomical sites with smaller volumes of soft tissue, using narrow connection cuffs and inflation pressures below 14 kPa.

Prognostic Value of Tissue Oxygen Saturation Using a Vascular Occlusion Test in Patients in the Early Phase of Multiorgan Dysfunction Syndrome

BACKGROUND

Multiple organ dysfunction syndrome (MODS) is a common disease pattern in intensive care units which is associated with an increased mortality. The aim of this study was to investigate whether a near-infrared spectroscopy (NIRS)-based noninvasive ischemia-reperfusion test (vascular occlusion test) using the parameter of tissue oxygen saturation (StO2) contains prognostic information for patients in the early phase of MODS.

METHODS

Within a period of 18 months between 2010 and 2012, 56 patients who newly developed MODS (≤24 h after diagnosis, Acute Physiology and Chronic Health Evaluation [APACHE] II score ≥20, subgroups: cardiogenic MODS [cMODS] and septic MODS [sMODS]) were included into the study. The StO2 was determined non-invasively in the area of the thenar muscles using a bedside NIRS device, InSpectra Tissue Spectrometer Model 650 (Hutchinson Technology Inc., Hutchinson, MN). The VOT was carried out by inflating a blood pressure cuff on the upper arm 30 mmHg above systolic blood pressure for 5 min. The parameters occlusion slope (OS) and recovery slope (RS) were recorded.

RESULTS

Fifteen patients with cMODS and 41 patients with sMODS were included in the study (age: 62.5 ± 14.4 years, 40 men and 16 women, APACHE II score: 34.6 ± 6.4). Twenty-eight-day-mortality was 55.4% (cMODS: 7 out of 15 patients, sMODS: 24 out of 41 patients). The measurement of StO2 while applying the VOT at baseline showed an OS of -11.7 ± 3.7%/min and an RS of 2.2 ± 1.5%/s. Survivors had significantly better values compared with non-survivors at baseline regarding OS (-12.8 ± 3.5%/min vs. -9.8 ± 3.4%/min; P = 0.016) and RS (2.6 ± 1.7%/s vs. 1.6 ± 1.0%/s; P = 0.022). Receiver-operating characteristic (ROC) curves show that the area under the curve (AUC) for OS was found to be significantly related to 28-day mortality (AUC: 0.7; 95% confidence interval [CI]: 0.56-0.85; P = 0.01). However, using both univariate and multivariate binary logistic regression models, RS was significantly associated with increased 28-day mortality (OR [univariate model]: 1.21 [95% CI: 1.1-1.8]; OR [multivariate model]: 1.23 [95% CI: 1.1-1.3]).

CONCLUSIONS

Impaired values of the VOT-parameters OS and RS are associated with an increased 28-day mortality in patients in the early phase of MODS.

The past, present, and prospective on UV-VIS-NIR skin photonics and spectroscopy-a wavelength guide

The study and applications of in vivo skin optics have been openly documented as early as the year 1954, or possibly earlier. To date, challenges in analyzing the complexities of this field remain, with wide scopes requiring more scrutiny. Recent advances in spectroscopic research and multivariate analytics allow a closer look into applications potentially for detecting or monitoring diseases. One of the challenges in this field is in establishing a reference for applications which correspond to certain bandwidths. This article reviews the scope on past research on skin spectroscopy, and the clinical aspects which have or may have applications on disease detection or enhancing diagnostics. A summary is supplied on the technicalities surrounding the measurements reported in literature, focused towards the wavelength-dependent applications in themes central to the respective research. Analytics on the topology of the papers' data cited in this work is also provided for a statistical perspective. In short, this paper strives to immediately inform the reader with possible applications via the spectroscopic devices at hand. Graphical Abstract .

Near-Infrared Spectroscopy to Monitor Nutritional Status of Neonates: A Review

The World Health Organization reported that half or more of all under five deaths were caused by undernutrition in developing countries, with the majority of these deaths occurring in the first week of life. Even if the undernourished neonates manage to survive, they are exposed to long-term health impacts, including obesity, cardiovascular disease, and hypertension. Along with those health-impacts they can be exposed to risks related to detrimental early development, such as physical impairment, stunting, brain dysfunction, and reduced cognitive development. Body fat percentage has been recognized to be closely associated with undernutrition in neonates. In this article, the potential of near infrared spectroscopy (NIRS), along with previous methods to measure body fat in neonates, is reviewed and discussed.

Review of early development of near-infrared spectroscopy and recent advancement of studies on muscle oxygenation and oxidative metabolism

Near-infrared spectroscopy (NIRS) has become an increasingly valuable tool to monitor tissue oxygenation (Toxy) in vivo. Observations of changes in the absorption of light with Toxy have been recognized as early as 1876, leading to a milestone NIRS paper by Jöbsis in 1977. Changes in the absorption and scatting of light in the 700-850-nm range has been successfully used to evaluate Toxy. The most practical devices use continuous-wave light providing relative values of Toxy. Phase-modulated or pulsed light can monitor both absorption and scattering providing more accurate signals. NIRS provides excellent time resolution (~ 10 Hz), and multiple source-detector pairs can be used to provide low-resolution imaging. NIRS has been applied to a wide range of populations. Continued development of NIRS devices in terms of lower cost, better detection of both absorption and scattering, and smaller size will lead to a promising future for NIRS studies.

Use of Near-infrared Spectroscopy and Implantable Doppler for Postoperative Monitoring of Free Tissue Transfer for Breast Reconstruction: A Systematic Review and Meta-analysis

BACKGROUND

Failure to accurately assess the perfusion of free tissue transfer (FTT) in the early postoperative period may contribute to failure, which is a source of major patient morbidity and healthcare costs. This systematic review and meta-analysis aim to evaluate and appraise current evidence for the use of near-infrared spectroscopy (NIRS) and/or implantable Doppler (ID) devices compared with conventional clinical assessment (CCA) for postoperative monitoring of FTT in reconstructive breast surgery.

METHODS

A systematic literature search was performed in accordance with the preferred reporting items for systematic reviews guidelines. Studies in human subjects published within the last decade relevant to the review question were identified. Meta-analysis using random-effects models of FTT failure rate and STARD scoring was then performed on the retrieved publications.

RESULTS

Nineteen studies met the inclusions criteria. For NIRS and ID, the mean sensitivity for the detection of FTT failure is 99.36% and 100% respectively, with average specificity of 99.36% and 97.63%, respectively. From studies with sufficient reported data, meta-analysis results demonstrated that both NIRS [OR = 0.09 (0.02-0.36); P < 0.001] and ID [OR = 0.39 (0.27-0.95); P = 0.04] were associated with significant reduction of FTT failure rates compared with CCA.

CONCLUSIONS

The use of ID and NIRS provided equivalent outcomes in detecting FTT failure and were superior to CCA. The ability to acquire continuous objective physiological data regarding tissue perfusion is a perceived advantage of these techniques. Reduced clinical staff workload and minimized hospital costs are also perceived as positive consequences of their use.

Pervasive wearable device for free tissue transfer monitoring based on advanced data analysis: clinical study report

Free tissue transfer (FTT) surgery for breast reconstruction following mastectomy has become a routine operation with high success rates. Although failure is low, it can have a devastating impact on patient recovery, prognosis, and psychological well-being. Continuous and objective monitoring of tissue oxygen saturation (StO2) has been shown to reduce failure rates through rapid detection time of postoperative vascular complications. We have developed a pervasive wearable wireless device that employs near-infrared spectroscopy (NIRS) to continuously monitor FTT via StO2 measurement. Previously tested on different models, the results of a clinical study are introduced. Our goal for the study is to demonstrate that the developed device can reliably detect StO2 variations in a clinical setting: 14 patients were recruited. Advanced data analysis was performed on the StO2 variations, the relative StO2 gradient change, and the classification of the StO2 within different clusters of blood occlusion level (from 0% to 100% at 25% step) based on previous studies made on a vascular phantom and animals. The outcomes of the clinical study concur with previous experimental results and the expected biological responses. This suggests that the device is able to correctly detect perfusion changes and provide real-time assessment on the viability of the FTT in a clinical setting.

Utility of a Finger-Mounted Tissue Oximeter with Near-Infrared Spectroscopy to Evaluate Limb Ischemia in Patients with Peripheral Arterial Disease

Objective: To investigate whether a finger-mounted tissue oximeter is useful in evaluating limb blood flow in patients with peripheral arterial disease (PAD).

Materials and Methods: Seventy-two patients with PAD were included, and the ankle-brachial index (ABI), transcutaneous oxygen pressure (TcPO₂), and skin perfusion pressure (SPP) were measured. The regional tissue oxygenation saturation (rSO₂) was measured using a finger-mounted tissue oximeter at the ankle, dorsal foot, and each dorsal and plantar toe. Correlations between rSO₂ and ABI and between TcPO₂ and SPP were analyzed. The patients were divided into three groups: Fontaine IIa (F-IIa), IIb (F-IIb), and III and IV (F-III/IV) groups. The difference in rSO₂ between each group was analyzed.

Results: Significant correlations were observed between rSO₂ and TcPO₂ and between rSO₂ and SPP. TcPO₂ and SPP in the F-III/IV group were significantly lower than those in the F-IIa group. rSO₂ in the F-IIb and F-III/IV groups was significantly lower than that in the F-IIa group.

Conclusion: The measurement of rSO₂ using finger-mounted tissue oximetry is quick, simple, and painless. It can be used on any skin area and is useful to evaluate limb circulation in patients with PAD.

Understanding near infrared spectroscopy and its application to skeletal muscle research

Near infrared spectroscopy (NIRS) is a powerful noninvasive tool with which to study the matching of oxygen delivery to oxygen utilization and the number of new publications utilizing this technique has increased exponentially in the last 20 yr. By measuring the state of oxygenation of the primary heme compounds in skeletal muscle (hemoglobin and myoglobin), greater understanding of the underlying control mechanisms that couple perfusive and diffusive oxygen delivery to oxidative metabolism can be gained from the laboratory to the athletic field to the intensive care unit or emergency room. However, the field of NIRS has been complicated by the diversity of instrumentation, the inherent limitations of some of these technologies, the associated diversity of terminology, and a general lack of standardization of protocols. This Cores of Reproducibility in Physiology (CORP) will describe in basic but important detail the most common methodologies of NIRS, their strengths and limitations, and discuss some of the potential confounding factors that can affect the quality and reproducibility of NIRS data. Recommendations are provided to reduce the variability and errors in data collection, analysis, and interpretation. The goal of this CORP is to provide readers with a greater understanding of the methodology, limitations, and best practices so as to improve the reproducibility of NIRS research in skeletal muscle.

Measurement and interpretation of hemoglobin concentration in clinical and field settings: a narrative review

Anemia affects over 800 million women and children globally. Defined as a limited or insufficient functional red blood cell supply in peripheral blood, anemia causes a reduced oxygen supply to tissues and can have serious health consequences for women and children. Hemoglobin (Hb) concentration is most commonly measured for anemia diagnosis. Methods to measure Hb are usually invasive (requiring a blood sample); however, advances in diagnostic and clinical chemistry over the past decade have led to the development of new noninvasive methods. Accurate diagnosis at the individual level is important to identify individuals who require treatment. At the population level, anemia prevalence estimates are often the impetus for national nutrition policies or programs. Thus, it is essential that methods for Hb measurement are sensitive, specific, accurate, and reproducible. The objective of our narrative review is to describe the basic principles, advantages, limitations, and quality control issues related to methods of Hb measurement in clinical and field settings. We also discuss other biomarkers and tests that can help to determine the severity and underlying causes of anemia. In conclusion, there are many established and emerging methods to measure Hb concentration, each with their own advantages, limitations, and factors to consider before use.

UBC-Nepal expedition: peripheral fatigue recovers faster in Sherpa than lowlanders at high altitude

KEY POINTS

The reduced oxygen tension of high altitude compromises performance in lowlanders. In this environment, Sherpa display superior performance, but little is known on this issue. Sherpa present unique genotypic and phenotypic characteristics at the muscular level, which may enhance resistance to peripheral fatigue at high altitude compared to lowlanders. We studied the impact of gradual ascent and exposure to high altitude (5050 m) on peripheral fatigue in age-matched lowlanders and Sherpa, using intermittent electrically-evoked contractions of the knee extensors. Peripheral fatigue (force loss) was lower in Sherpa during the first part of the protocol. Post-protocol, the rate of force development and contractile impulse recovered faster in Sherpa than in lowlanders. At any time, indices of muscle oxygenation were not different between groups. Muscle contractile properties in Sherpa, independent of muscle oxygenation, were less perturbed by non-volitional fatigue. Hence, elements within the contractile machinery contribute to the superior physical performance of Sherpa at high altitude.

ABSTRACT

Altitude-related acclimatisation is characterised by marked muscular adaptations. Lowlanders and Sherpa differ in their muscular genotypic and phenotypic characteristics, which may influence peripheral fatigability at altitude. After gradual ascent to 5050 m, 12 lowlanders and 10 age-matched Sherpa (32 ± 10 vs. 31 ± 11 years, respectively) underwent three bouts (separated by 15 s rest) of 75 intermittent electrically-evoked contractions (12 pulses at 15 Hz, 1.6 s between train onsets) of the dominant leg quadriceps, at the intensity which initially evoked 30% of maximal voluntary force. Trains were also delivered at minutes 1, 2 and 3 after the protocol to measure recovery. Tissue oxygenation index (TOI) and total haemoglobin (tHb) were quantified by a near-infrared spectroscopy probe secured over rectus femoris. Superficial femoral artery blood flow was recorded using ultrasonography, and delivery of oxygen was estimated (eDO₂ ). At the end of bout 1, peak force was greater in Sherpa than in lowlanders (91.5% vs. 84.5% baseline, respectively; P < 0.05). Peak rate of force development (pRFD), the first 200 ms of the contractile impulse (CI₂₀₀ ), and half-relaxation time (HRT) recovered faster in Sherpa than in lowlanders (percentage of baseline at 1 min: pRFD: 89% vs. 74%; CI₂₀₀ : 91% vs. 80%; HRT: 113% vs. 123%, respectively; P < 0.05). Vascular measures were pooled for lowlanders and Sherpa as they did not differ during fatigue or recovery (P < 0.05). Mid bout 3, TOI was decreased (90% baseline) whereas tHb was increased (109% baseline). After bout 3, eDO₂ was markedly increased (1266% baseline). The skeletal muscle of Sherpa seemingly favours repeated force production at altitude for similar oxygen delivery compared to lowlanders.

A Self-Calibrated Tissue Viability Sensor for Free Flap Monitoring

In fasciocutaneous free flap surgery, close postoperative monitoring is crucial for detecting flap failure, as around 10% of cases require additional surgery due to compromised anastomosis. Different biochemical and biophysical techniques have been developed for continuous flap monitoring, however, they all have shortcoming in terms of reliability, elevated cost, potential risks to the patient, and inability to adapt to the patient's phenotype. A wearable wireless device based on near infrared spectroscopy has been developed for continuous blood flow and perfusion monitoring by quantifying tissue oxygen saturation (). This miniaturized and low-cost device is designed for postoperative monitoring of flap viability. With self-calibration, the device can adapt itself to the characteristics of the patients' skin such as tone and thickness. An extensive study was conducted with 32 volunteers. The experimental results show that the device can obtain reliable measurements across different phenotypes (age, sex, skin tone, and thickness). To assess its ability to detect flap failure, the sensor was tested in a pilot animal study. Free groin flaps were performed on 16 Sprague Dawley rats. Results demonstrate the accuracy of the sensor in assessing flap viability and identifying the origin of failure (venous or arterial thrombosis).

Continual near-infrared spectroscopy monitoring in the injured lower limb and acute compartment syndrome: an FDA-IDE trial

Aims

The aim of this study was to evaluate near-infrared spectroscopy (NIRS) as a continuous, non-invasive monitor for acute compartment syndrome (ACS).

Patients and Methods

NIRS sensors were placed on 86 patients with, and 23 without (controls), severe leg injury. NIRS values were recorded for up to 48 hours. Longitudinal data were analyzed using summary and graphical methods, bivariate comparisons, and multivariable multilevel modelling.

Results

Mean NIRS values in the anterior, lateral, superficial posterior, and deep posterior compartments were between 72% and 78% in injured legs, between 69% and 72% in uninjured legs, and between 71% and 73% in bilaterally uninjured legs. In patients without ACS, the values were typically > 3% higher in injured compartments. All seven limbs with ACS had at least one compartment where NIRS values were 3% or more below a reference uninjured control compartment. Missing data were encountered in many instances.

Conclusion

NIRS oximetry might be used to aid the assessment and management of patients with ACS. Sustained hyperaemia is consistent with the absence of ACS in injured legs. Loss of the hyperaemic differential warrants heightened surveillance. NIRS values in at least one injured compartment(s) were > 3% below the uninjured contralateral compartment(s) in all seven patients with ACS. Additional interventional studies are required to validate the use of NIRS for ACS monitoring. Cite this article: Bone Joint J 2018;100-B:787-97.

Using near-infrared reflectance spectroscopy (NIRS) to assess distal-limb perfusion on venoarterial (V-A) extracorporeal membrane oxygenation (ECMO) patients with femoral cannulation

Background:

Patients requiring V-A ECMO who receive femoral cannulation have an associated risk of distal, lower-limb hypoperfusion and ischemia of the cannulated leg. This pilot study evaluated the usefulness of non-invasive lower-limb oximetry, using near-infrared reflectance spectroscopy (NIRS) to detect limb ischemia.

Methods:

Between June 2016 and January 2017, 25 patients receiving femoral V-A ECMO were continuously monitored using the CASMED Fore-Sight Elite (CAS Medical Systems Inc., Branford, CT) tissue oximeter. A retrospective pilot study was conducted to review the correlation between NIRS tissue saturations (StO2) and clinical indications of limb ischemia. Patients were monitored for StO2s less than 50% for more than four minutes or StO2 differentials between the cannulated and non-cannulated legs greater than 15%.

Results:

Twenty-five patients (age 22-78) were monitored with NIRS. Six patients had clinical indications of lower-limb ischemia: cold limb, mottled skin and pulseless Doppler ultrasound. All six patients had StO2s below 50% that persisted for longer than four minutes. Of the 25 patients, one patient had a false-positive indication of hypoperfusion with StO2 below 50% for more than four minutes due to a venous saturation below 30%. Another patient had a false-positive pulseless Doppler ultrasound caused by high doses of pressor support. The StO2 was greater than 60%, which confirmed the clinical determination of adequate perfusion. Five patients had StO2s below 50% for less than four minutes and none of these patients had clinical indications of lower-limb hypoperfusion. All patients with cannula-related obstruction of flow to the distal portion of the leg had StO2 differentials greater than 15%. No patients without cannula-related obstruction to flow had StO2 differentials greater than 15%.

Conclusion:

Advancements in NIRS technology seem to have improved its accuracy for continuous, non-invasive monitoring of regional tissue and may provide clinicians with an additional metric to protect the distal portion of the cannulated leg.

Splanchnic NIRS monitoring in neonatal care: rationale, current applications and future perspectives

Near infrared spectroscopy (NIRS) provides a non-invasive, continuous monitoring of regional tissue oxygenation. NIRS assessment of neonatal splanchnic oxygenation (SrSO₂) has gained increasing interest over the last decade, as local hypoxia and ischemia underlie the most feared gut complications in neonates. Current literature provides encouraging evidence in support of SrSO₂ reliability in detecting mesenteric hemodynamic changes related to various physiological and pathological conditions in-term and preterm infants. Even so, while splanchnic NIRS monitoring looks promising for investigating gut physiopathology in research settings, further studies are needed to evaluate its feasibility as a routine monitoring tool in neonatal care and to investigate its potential role in clinical decision making. After a brief introduction to NIRS technical principles, this review aims to provide a complete overview of current neonatal applications for splanchnic NIRS monitoring, to discuss its possible limitations and to suggest future directions for research and clinical applications.

Cerebral and muscle microvascular oxygenation in children with sickle cell disease: Influence of hematology, hemorheology and vasomotion

The present study investigated cerebral and muscle hemoglobin oxygen saturation (tissue oxygen index, TOI) in children with sickle cell anemia (SS), sickle cell hemoglobin C disease (SC) and healthy children (AA). TOI was measured by near-infrared spectroscopy (NIRS) and spectral analysis of the TOI variability was used to assess flowmotion and vasomotion. Arterial oxyhemoglobin saturation (SpO₂), hemorheological and hematological parameters were also measured in SS and SC children. Both TOI were lower in SS compared to both AA and SC children, with SC exhibiting lower values than AA children. Cerebral vasomotion expressed in absolute values was enhanced in SS compared to AA and SC children. Muscle vasomotion did not differ between the three groups. Hematocrit, SpO₂ and red blood cell deformability were positively associated with cerebral TOI in SS children. We demonstrated that 1) cerebral and muscle TOI were markedly decreased in SS children while the decrease of TOI was milder in SC children, 2) cerebral TOI level was associated with several biological markers in SS children only and 3) cerebral vasomotion was enhanced in SS, possibly to counterbalance the effects of chronic cerebral hypoxia.