Localized irregularities in hemoglobin flow and oxygenation in calf muscle in patients with peripheral vascular disease detected with near-infrared spectrophotometry

Near-infrared spectroscopy with a provocative maneuver to detect the presence of severe peripheral arterial disease

Current assessment standards for peripheral arterial disease (PAD), such as the ankle brachial index, are limited in their utility and portability. Near-infrared spectroscopy (NIRS) has shown some promise in diagnosing PAD when used in conjunction with a provocative maneuver. The purpose of this study was to assess the viability of NIRS in conjunction with a transient leg elevation provocative maneuver for detecting severe PAD. This retrospective observational cross-sectional study assessed 57 limbs in 34 patients receiving routine vascular screening for PAD at Madigan Army Medical Center. The patient limbs were stratified into normal (n = 17), mild (n = 9), moderate (n = 16), and severe (n = 15) PAD groups based on the clinician assessments. Additionally, the patients were assessed with NIRS measurements taken with the patient in the supine position at rest and using a provocative leg raise maneuver of transient leg elevation of 45° for 60 seconds. The resting tissue oxygen saturation (StO2) and the change in StO2 (ΔStO2) from rest to elevation were recorded and compared between the PAD severity groups via independent measures analysis of variance with the Tukey honest significant difference post hoc test. The supine resting StO2 was not different between the normal (77.5% ± 7.7%), mild (72.5% ± 7.4%), moderate (72.0% ± 10.3%), and severe (74.2% ± 5.4%) PAD groups (P = .23). However, the ΔStO2 with transient leg elevation was significantly greater in the severe PAD group (-17.2% ± 6.0%) compared with the normal (-3.9% ± 4.8%), mild (-6.9% ± 4.7%), and moderate (-9.7% ± 5.2%) PAD groups (P < .002 for all). Similar results were observed in the changes in oxyhemoglobin and deoxyhemoglobin. The leg elevation protocol was also used for two patients before and after lower limb revascularization, which demonstrated that the ΔStO2 corresponded with the clinical assessment of PAD severity. Resting supine NIRS images were unable to detect any differences among normal and limbs with different PAD severity. However, NIRS imaging with 45° leg elevation for 60 seconds showed a significant difference between severe PAD compared healthy patients and those with mild to moderate PAD in a fast, precise, and accurate manner. These preliminary data support the use of NIRS and transient leg elevation as a tool to diagnose severe PAD but do not support the use of NIRS alone as a screening test for PAD. NIRS measurements with leg elevation might be a viable noninvasive, noncontact, and portable method of assessing severe PAD for home monitoring, in rural communities, and/or in standard clinical practice.

A comprehensive overview of diffuse correlation spectroscopy: Theoretical framework, recent advances in hardware, analysis, and applications

Diffuse correlation spectroscopy (DCS) is a powerful tool for assessing microvascular hemodynamic in deep tissues. Recent advances in sensors, lasers, and deep learning have further boosted the development of new DCS methods. However, newcomers might feel overwhelmed, not only by the already-complex DCS theoretical framework but also by the broad range of component options and system architectures. To facilitate new entry to this exciting field, we present a comprehensive review of DCS hardware architectures (continuous-wave, frequency-domain, and time-domain) and summarize corresponding theoretical models. Further, we discuss new applications of highly integrated silicon single-photon avalanche diode (SPAD) sensors in DCS, compare SPADs with existing sensors, and review other components (lasers, sensors, and correlators), as well as data analysis tools, including deep learning. Potential applications in medical diagnosis are discussed and an outlook for the future directions is provided, to offer effective guidance to embark on DCS research.

Comparing Non-Invasive Spectrophotometry to Hematology Analysis for Hemoglobin Measurements in Sickle Cell Disease Patients

Patients with sickle cell disease (SCD) require repeated blood sampling for hemoglobin (Hb) concentration measurements. The primary aim of this study was to compare non-invasive spectrophotometric hemoglobin (SpHb, g/dL) measurements to those taken via an automated hematology analyzer (Hb, g/dL) in patients with SCD visiting outpatient clinics and to investigate the correlations and agreements between both measurement techniques. Secondarily, we aimed to identify the SpHb cut-off concentration for the diagnosis of anemia and to monitor the effects of the pleth variability index (PVI, %) and perfusion index (PI) on SpHb measurements. The results gained from the examination of one hundred and fifty-eight patients indicated that the SpHb measurements overestimated the lab Hb concentrations, with a mean (SpHb-Hb) bias of 0.82 g/dL (SD 1.29). The SpHb measurements were positively correlated with the Hb measurements (Kendall's tau correlation (τ), n = 158, τ = 0.68, p < 0.001), with an intra-class correlation (ICC) of 0.67 and a 95% CI from 0.57 to 0.74 (p = 0.000). The SpHb cut-off concentration to diagnose anemia was 11.4 and 11.7 g/dL for males and females, respectively. SpHb sensitivity was low for males and females at 64.4% and 57.1%; however, the specificity was higher at 90.9% and 75%, with positive predictive values (PPVs) of 95.6 and 85.7, respectively. No correlation existed between SpHb measurements and the PVI (%) in contrast with a moderate correlation with the PI (r = 0.049, p = 0.54, and r = 0.36, p < 0.001, respectively). The mean PI was low at 2.52 ± 1.7. In conclusion, the SpHb measurements were consistently higher than the lab Hb concentrations, with a positive correlation. The sensitivity and precision of the SpHb measurements were lower than expected. However, the SpHb specificity and its positive predictive values (PPVs) indicated that it is less likely for a patient with a positive SpHb test result for anemia to be non-anemic. These results will allow SpHb measurement to play a role in excluding the presence of anemia. In light of the low PI values determined, the SpHb measurements were challenging to take and, thus, require further technological improvements.

Near infrared spectroscopy in peripheral artery disease and the diabetic foot: A systematic review

With the need for tools that assess microvascular status in diabetic foot disease (DFD) being clear, near infrared spectroscopy (NIRS) is a putative method for noninvasive testing of the diabetic foot. The use of NIRS in patients with peripheral arterial disease (PAD) has extended to its role in studying the pathophysiology of DFD. NIRS generates metrics such as recovery time, deoxygenation, oxygen consumption (VO₂ ), tissue oxygen saturation (StO₂ ), total haemoglobin (HbT), and oxyhaemoglobin area under the curve (O₂ Hb_AUC ). NIRS may potentially help the multidisciplinary team stratify limbs as high-risk, especially in diabetic patients with symptoms masked by peripheral neuropathy. NIRS may be useful for assessing treatment effectiveness and preventing deterioration of patients with PAD.

Simultaneous measurements of tissue blood flow and oxygenation using a wearable fiber-free optical sensor

SIGNIFICANCE

There is an essential need to develop wearable multimodality technologies that can continuously measure both blood flow and oxygenation in deep tissues to investigate and manage various vascular/cellular diseases.

AIM

To develop a wearable dual-wavelength diffuse speckle contrast flow oximetry (DSCFO) for simultaneous measurements of blood flow and oxygenation variations in deep tissues.

APPROACH

A wearable fiber-free DSCFO probe was fabricated using 3D printing to confine two small near-infrared laser diodes and a tiny CMOS camera in positions for DSCFO measurements. The spatial diffuse speckle contrast and light intensity measurements at the two different wavelengths enable quantification of tissue blood flow and oxygenation, respectively. The DSCFO was first calibrated using tissue phantoms and then tested in adult forearms during artery cuff occlusion.

RESULTS

Phantom tests determined the largest effective source-detector distance (15 mm) and optimal camera exposure time (10 ms) and verified the accuracy of DSCFO in measuring absorption coefficient variations. The DSCFO detected substantial changes in forearm blood flow and oxygenation resulting from the artery occlusion, which meet physiological expectations and are consistent with previous study results.

CONCLUSIONS

The wearable DSCFO may be used for continuous and simultaneous monitoring of blood flow and oxygenation variations in freely behaving subjects.

Photoacoustic imaging of hemodynamic changes in forearm skeletal muscle during cuff occlusion

Characterizations of circulatory and metabolic function in skeletal muscle are of great importance in clinical settings. Here in this study, we investigate the utility of photoacoustic tomography (PAT) to monitor the hemodynamic changes in forearm skeletal muscle during cuff occlusion. We show high quality photoacoustic (PA) images of human forearm in comparison with ultrasound images. Besides, we track the hemodynamic changes in the forearm during cuff occlusion cross-validated with near-infrared spectroscopy. Our study suggests that PAT, as a new tool, could be applied to common diseases affecting skeletal muscle in the future.

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.

Near infrared spectroscopy-guided exercise training for claudication in peripheral arterial disease

Rationale

Supervised treadmill exercise for claudication in peripheral arterial disease is effective but poorly tolerated because of ischemic leg pain. Near infrared spectroscopy allows non-invasive detection of muscle ischemia during exercise, allowing for characterization of tissue perfusion and oxygen utilization during training.

Objective

We evaluated walking time, muscle blood flow, and muscle mitochondrial capacity in patients with peripheral artery disease after a traditional pain-based walking program and after a muscle oxygen-guided walking program.

Method and results

Patients with peripheral artery disease trained thrice weekly in 40-minute-long sessions for 12 weeks, randomized to oxygen-guided training ( n = 8, age 72 ± 9.7 years, 25% female) versus traditional pain-based training ( n = 10, age 71.6 ± 8.8 years, 20% female). Oxygen-guided training intensity was determined by maintaining a 15% reduction in skeletal muscle oxygenation by near infrared spectroscopy rather than relying on symptoms of pain to determine exercise effort. Pain free and maximal walking times were measured with a 12-minute Gardner treadmill test. Gastrocnemius mitochondrial capacity and blood flow were measured using near infrared spectroscopy. Baseline pain-free walking time was similar on a Gardner treadmill test (2.5 ± 0.9 vs. 3.6 ± 1.0 min, p = 0.5). After training, oxygen-guided cohorts improved similar to pain-guided cohorts (pain-free walking time 6.7 ± 0.9 vs. 6.9 ± 1.1 min, p < 0.01 for change from baseline and p = 0.97 between cohorts). Mitochondrial capacity improved in both groups but more so in the pain-guided cohort than in the oxygen-guided cohort (38.8 ± 8.3 vs. 14.0 ± 9.3, p = 0.018). Resting muscle blood flow did not improve significantly in either group with training.

Conclusions

Oxygen-guided exercise training improves claudication comparable to pain-based training regimens. Adaptations in mitochondrial function rather than increases in limb perfusion may account for functional improvement. Increases in mitochondrial oxidative capacity may be proportional to the degree of tissue hypoxia during exercise.

Measuring reactive hyperemia in the lower limb using near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) has been used to measure reactive hyperemia following a vascular occlusion. However, the procedures and methods of analysis used have varied. The purpose of the present study is to identify reproducible methods for measuring reactive hyperemia using HbO2 NIRS signals in the calf and foot. Healthy participants (10 male, 10 female) aged 19 to 28 years performed one of two tests: reproducibility trials or elevation protocol (30 and 60 cm limb elevation above the heart). The time to 50% reperfusion (T1/2) and the second (R2q) quartile rates of reperfusion were found to be the most reproducible parameters (coefficient of variation= 7.12 to 14.1%). The time to 95% reperfusion (T95) was 12.7% more reproducible on average than the previously reported parameter of time to peak hyperemia. Measures of reperfusion time and rate slowed with increasing limb elevation. Correlations were identified between the calf and foot in the measurements of R2q (R2 = 0.713, p = 0.021), T1/2 (R2 = 0.673, p = 0.033), and T95 (R2 = 0.792, p = 0.006). Half and 95% recovery times and second and third quartile rates expressed good reproducibility and sensitivity to change with reduced perfusion pressure. NIRS measures of reactive hyperemia have the potential to evaluate microvascular perfusion in clinical populations.

Recent developments in near-infrared spectroscopy (NIRS) for the assessment of local skeletal muscle microvascular function and capacity to utilise oxygen

Purpose of review

Continuous wave near infrared spectroscopy (CW NIRS) provides non-invasive technology to measure relative changes in oxy- and deoxy-haemoglobin in a dynamic environment. This allows determination of local skeletal muscle O₂ saturation, muscle oxygen consumption (V˙O2) and blood flow. This article provides a brief overview of the use of CW NIRS to measure exercise-limiting factors in skeletal muscle.

Recent findings

NIRS parameters that measure O₂ delivery and capacity to utilise O₂ in the muscle have been developed based on response to physiological interventions and exercise. NIRS has good reproducibility and agreement with gold standard techniques and can be used in clinical populations where muscle oxidative capacity or oxygen delivery (or both) are impaired. CW NIRS has limitations including: the unknown contribution of myoglobin to the overall signals, the impact of adipose tissue thickness, skin perfusion during exercise, and variations in skin pigmentation. These, in the main, can be circumvented through appropriate study design or measurement of absolute tissue saturation.

Summary

CW NIRS can assess skeletal muscle O₂ delivery and utilisation without the use of expensive or invasive procedures and is useable in large population-based samples, including older adults.

•

An overview of CW NIRS to measure O₂ utilisation and delivery is presented.

•

CW NIRS is cheap, non-invasive, portable and useable in population-based samples.

•

It is useful for understanding underlying mechanisms of deterioration in capacity.

Avaliação da saturação tecidual de oxigênio durante o sintoma claudicante em pacientes com doença arterial periférica

Resumo Contexto O relato de sintoma claudicante em pacientes com doença arterial periférica é utilizado como modulador da intensidade de exercício físico para o tratamento clínico, entretanto os valores de oxigenação tecidual nesse momento são desconhecidos. Objetivo Descrever o suprimento tecidual de oxigênio por meio da espectroscopia de luz próxima ao infravermelho ou Near-Infrared Spectroscopy (NIRS) nos momentos em que o paciente relata sintoma claudicante inicial e máximo em testes de exercício. Métodos Nove pacientes, oito homens com 65,63 ± 6,02 anos de idade, previamente diagnosticados com doença arterial periférica, realizaram teste de exercício de carga constante e de carga incremental com monitorização do nível de oxigenação tecidual através da NIRS. As saturações de oxigênio obtidas no momento em que o paciente relata sintoma claudicante inicial e no momento em que relata sintoma claudicante máximo foram comparadas com os valores de saturação da manobra de oclusão arterial por meio do intervalo de confiança de 95% da diferença. Resultados Verificou-se que os valores de saturação nos momentos de sintoma claudicante inicial e máximo são estatisticamente distintos quando comparados àqueles obtidos na manobra de oclusão arterial, entretanto, através da análise percentual do quão distante esses valores encontram-se é possível observar que, do ponto de vista clínico, eles estão próximos. Conclusões A saturação no momento em que o paciente relata sintomas claudicantes inicial e máximo é bastante próxima do valor de saturação no momento de oclusão e do ponto de vista clínico o relato subjetivo de sintoma do paciente é adequado como parâmetro para a prescrição do exercício físico.

Development of a luminous textile for reflective pulse oximetry measurements

In this paper, a textile-based sensing principle for long term photopletysmography (PPG) monitoring is presented. Optical fibers were embroidered into textiles such that out-coupling and in-coupling of light was possible. The "light-in light-out" properties of the textile enabled the spectroscopic characterization of human tissue. For the optimization of the textile sensor, three different carrier fabrics and different fiber modifications were compared. The sample with best light coupling efficiency was successfully used to measure heart rate and SpO2 values of a subject. The latter was determined by using a modified Beer-Lambert law and measuring the light attenuation at two different wavelengths (632 nm and 894 nm). Moreover, the system was adapted to work in reflection mode which makes the sensor more versatile. The measurements were additionally compared with commercially available system and showed good correlation.

Evaluation of a textile-based near infrared spectroscopy system in calf muscle oxygenation measurements

We recently introduced a novel textile-based NIRS sensor (TexNIRS). Here, we evaluate TexNIRS in ten subjects (16 legs, age 28.5 ± 2.32 years, adipose tissue thickness (ATT) 4.17 ± 1.71 mm). Three venous occlusions at 50 mmHg were performed on their calf muscle. After 3 min of occlusion, oxy/deoxy hemoglobin concentration ([O₂Hb], [HHb]) changes were 3.71 ± 1.89/1.79 ± 1.08 μM; venous oxygen saturation (SvO₂) was 75 ± 9.7 %, oxygen consumption (VO₂) was 0.02 ± 0.01 mL/100 g/min, hemoglobin flow (HF) was 0.93 ± 0.48 μmol/100 mL/min, and blood flow (BF) was 2.01 ± 1.04 mL/100 mL/min. Our results are in good agreement with the literature, but the TexNIRS enables a much higher level of comfort.

Simultaneous measurement of deep tissue blood flow and oxygenation using noncontact diffuse correlation spectroscopy flow-oximeter

We report a novel noncontact diffuse correlation spectroscopy flow-oximeter for simultaneous quantification of relative changes in tissue blood flow (rBF) and oxygenation (Δ[oxygenation]). The noncontact probe was compared against a contact probe in tissue-like phantoms and forearm muscles (n = 10), and the dynamic trends in both rBF and Δ[oxygenation] were found to be highly correlated. However, the magnitudes of Δ[oxygenation] measured by the two probes were significantly different. Monte Carlo simulations and phantom experiments revealed that the arm curvature resulted in a significant underestimation (~−20%) for the noncontact measurements in Δ[oxygenation], but not in rBF. Other factors that may cause the residual discrepancies between the contact and noncontact measurements were discussed, and further comparisons with other established technologies are needed to identify/quantify these factors. Our research paves the way for noncontact and simultaneous monitoring of blood flow and oxygenation in soft and vulnerable tissues without distorting tissue hemodynamics.

Dynamic diffuse optical tomography imaging of peripheral arterial disease

Peripheral arterial disease (PAD) is the narrowing of arteries due to plaque accumulation in the vascular walls. This leads to insufficient blood supply to the extremities and can ultimately cause cell death. Currently available methods are ineffective in diagnosing PAD in patients with calcified arteries, such as those with diabetes. In this paper we investigate the potential of dynamic diffuse optical tomography (DDOT) as an alternative way to assess PAD in the lower extremities. DDOT is a non-invasive, non-ionizing imaging modality that uses near-infrared light to create spatio-temporal maps of oxy- and deoxy-hemoglobin in tissue. We present three case studies in which we used DDOT to visualize vascular perfusion of a healthy volunteer, a PAD patient and a diabetic PAD patient with calcified arteries. These preliminary results show significant differences in DDOT time-traces and images between all three cases, underscoring the potential of DDOT as a new diagnostic tool.

Noninvasive optical quantification of absolute blood flow, blood oxygenation, and oxygen consumption rate in exercising skeletal muscle

This study investigates a method using novel hybrid diffuse optical spectroscopies [near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS)] to obtain continuous, noninvasive measurement of absolute blood flow (BF), blood oxygenation, and oxygen consumption rate (V̇O(2)) in exercising skeletal muscle. Healthy subjects (n=9) performed a handgrip exercise to increase BF and V̇O(2) in forearm flexor muscles, while a hybrid optical probe on the skin surface directly monitored oxy-, deoxy-, and total hemoglobin concentrations ([HbO(2)], [Hb], and THC), tissue oxygen saturation (S(t)O(2)), relative BF (rBF), and relative oxygen consumption rate (rV̇O(2)). The rBF and rV̇O(2) signals were calibrated with absolute baseline BF and V̇O(2) obtained through venous and arterial occlusions, respectively. Known problems with muscle-fiber motion artifacts in optical measurements during exercise were mitigated using a novel gating algorithm that determined muscle contraction status based on control signals from a dynamometer. Results were consistent with previous findings in the literature. This study supports the application of NIRS/DCS technology to quantitatively evaluate hemodynamic and metabolic parameters in exercising skeletal muscle and holds promise for improving diagnosis and treatment evaluation for patients suffering from diseases affecting skeletal muscle and advancing fundamental understanding of muscle and exercise physiology.

Terminal arteriolar network structure/function and plasma cytokine levels in db/db and ob/ob mouse skeletal muscle

OBJECTIVE

To investigate the terminal arteriolar network structure and function in relation to circulating plasma cytokine levels in db/db, ob/ob, and their genetic background control, C57/bl6, mice.

METHODS

Arteriolar network size and erythrocyte distribution were observed in the resting cremaster muscle (n = 45, pentobarbital 50 mg/kg i.p.). Structural remodeling and inflammatory state were related to 21 plasma cytokine levels.

RESULTS

db/db networks were shorter, had fewer branches, and smaller diameters than C57/bl6 controls. ob/ob networks were longer, with similar branch numbers, however with non-uniform diameters. Shunting of erythrocytes to the specific terminal arteriolar branches of the network (functional rarefaction) was prominent in db/db and ob/ob, with further evidence of shunting between networks seen as no flow to 50% of ob/ob arteriolar networks.

CONCLUSIONS

Altered levels of plasma cytokines are consistent with structural remodeling seen in db/db, and a pro-inflammatory state for both db/db and ob/ob. Differences in network structure alone predict overall reduced uniform oxygen delivery in db/db or ob/ob. Shunting probably increases heterogeneous oxygen delivery and is strain-dependent.

Intraoperative evaluation of revascularization effect on ischemic muscle hemodynamics using near-infrared diffuse optical spectroscopies

Arterial revascularization in patients with peripheral arterial disease (PAD) reestablishes large arterial blood supply to the ischemic muscles in lower extremities via bypass grafts or percutaneous transluminal angioplasty (PTA). Currently no gold standard is available for assessment of revascularization effects in lower extremity muscles. This study tests a novel near-infrared diffuse correlation spectroscopy flow-oximeter for monitoring of blood flow and oxygenation changes in medial gastrocnemius (calf) muscles during arterial revascularization. Twelve limbs with PAD undergoing revascularization were measured using a sterilized fiber-optic probe taped on top of the calf muscle. The optical measurement demonstrated sensitivity to dynamic physiological events, such as arterial clamping/releasing during bypass graft and balloon inflation/deflation during PTA. Significant elevations in calf muscle blood flow were observed after revascularization in patients with bypass graft (+48.1 ± 17.5%) and patients with PTA (+43.2 ± 11.0%), whereas acute post-revascularization effects in muscle oxygenation were not evident. The decoupling of flow and oxygenation after revascularization emphasizes the need for simultaneous measurement of both parameters. The acute elevations/improvements in calf muscle blood flow were associated with significant improvements in symptoms and functions. In total, the investigation corroborates potential of the optical methods for objectively assessing the success of arterial revascularization.

Simultaneous absolute measures of glabrous skin hemodynamic and light-scattering change in response to formalin injection in rats

Subcutaneous injection of formalin is a well-known model to study the nature of inflammatory pain. One of the cardinal signs of inflammation is redness, as a result of increased blood perfusion. We used an optical technology, light reflectance spectroscopy, to noninvasively obtain absolute measures of cutaneous hemodynamic components, including the concentrations of oxy- ([HbO]), deoxy- ([Hb]), total-hemoglobin ([HbT]), oxygen saturation (SO(2)), and the reduced light-scattering coefficient (μs'). The objective is to assess the effect of formalin-induced skin inflammation on the aforementioned parameters. Six rats were injected with formalin (50 μl, 3%) into left hind paw under pentobarbital anesthesia. Our results indicate prolonged increases in [HbO], [HbT], and SO(2) post injection only in the ipsilateral side. No statistically significant changes in [Hb] and μ(s)' occurred in either side. The arterial blood influx tends to be the major attribute of local hyperemia during inflammation. Thereby, [HbO] appears to be superior to [Hb] in measuring inflammation. In conclusion, the needle-probe-based light reflectance can be a feasible means to obtaining absolute measures of skin hemodynamic and light-scattering parameters when studying inflammatory pain.

Effects of muscle fiber motion on diffuse correlation spectroscopy blood flow measurements during exercise

The influence of muscle fiber motion during exercise on diffuse correlation spectroscopy (DCS) measurements of skeletal muscle blood flow is explored. Isotonic (with muscle fiber motion) and isometric (without muscle fiber motion) plantar flexion exercises were performed at 30% of maximal force on a dynamometer, and muscle blood flow was continuously monitored on the medial gastrocnemius (calf) muscle of a healthy volunteer using DCS. During exercise, dynamometer recordings including footplate position, footplate angular velocity, and plantar flexion torque were obtained. Muscle fiber motions introduced artifacts into the DCS signals, causing an overestimation of blood flow changes. We show how proper co-registration of dynamometer recordings and DCS measurements enables separation of the true blood flow responses during exercise from those affected by the motion artifacts.

Combining microdialysis and near-infrared spectroscopy for studying effects of low-load repetitive work on the intramuscular chemistry in trapezius myalgia

Epidemiological research provides strong evidence for a link between repetitive work (RW) and the development of chronic trapezius myalgia (TM). The aims were to further elucidate if an accumulation of sensitising substances or impaired oxygenation is evident in painful muscles during RW. Females with TM (n = 14) were studied during rest, 30 minutes RW and 60 minutes recovery. Microdialysate samples were obtained to determine changes in intramuscular microdialysate (IMMD) [glutamate], [PGE₂], [lactate], and [pyruvate] (i.e., [concentration]) relative to work. Muscle oxygenation (%StO₂) was assessed using near-infrared spectroscopy. During work, all investigated substances, except PGE₂, increased significantly: [glutamate] (54%, P < .0001), [lactate] (26%, P < .005), [pyruvate] (19%, P < .0001), while the %StO₂ decreased (P < .05). During recovery [PGE₂] decreased (P < .005), [lactate] remained increased (P < .001), [pyruvate] increased progressively (P < .0001), and %StO₂ had returned to baseline. Changes in substance concentrations and oxygenation in response to work indicate normal increase in metabolism but no ongoing inflammation in subjects with TM.

Resting Muscle Oxygen Consumption by Near-Infrared Spectroscopy in Peripheral Arterial Disease: A Parameter to be Considered in a Clinical Setting?

Resting muscle VO 2 consumption (rmVO2) as measured by near-infrared spectroscopy (NIRS) has been poorly studied in peripheral arterial disease (PAD). We studied the feasibility of its assessment in a clinical setting, compared values from PAD and healthy participants, and identified factors affecting rmVO 2 in PAD. A total of 119 PAD patients with claudication and 30 healthy participants were enrolled. Ankle brachial index (ABI), adipose tissue thickness, and rmVO2 in the gastrocnemius after venous (rmVO2ven) or arterial (rmVO2art) occlusion were measured with NIRS. Compared to rmVO2art, rmVO2ven determination was less painful (P = .001), with higher values (P < .0001). rmVO2ven of PAD patients was not significantly different from healthy participants and was inversely correlated with the corresponding ABI (P = .018). rmVO2ven from severely diseased legs was higher than values from borderline/moderately diseased legs (P = .003). The determination of rmVO2ven by NIRS is suitable for the clinical setting and allows noninvasive quantification of a compensatory peripheral adaptation in patients with PAD.

Microcirculatory changes and skeletal muscle oxygenation measured at rest by non-infrared spectroscopy in patients with and without diabetes undergoing haemodialysis

Introduction

Haemodialysis has direct and indirect effects on skin and muscle microcirculatory regulation that are severe enough to worsen tolerance to physical exercise and muscle asthenia in patients undergoing dialysis, thus compromising patients' quality of life and increasing the risk of mortality. In diabetes these circumstances are further complicated, leading to an approximately sixfold increase in the incidence of critical limb ischaemia and amputation. Our aim in this study was to investigate in vivo whether haemodialysis induces major changes in skeletal muscle oxygenation and blood flow, microvascular compliance and tissue metabolic rate in patients with and without diabetes.

Methods

The study included 20 consecutive patients with and without diabetes undergoing haemodialysis at Sant Andrea University Hospital, Rome from March to April 2007. Near-infrared spectroscopy (NIRS) quantitative measurements of tissue haemoglobin concentrations in oxygenated [HbO₂] and deoxygenated forms [HHb] were obtained in the calf once hourly for 4 hours during dialysis. Consecutive venous occlusions allowed one to obtain muscular blood flow (mBF), microvascular compliance and muscle oxygen consumption (mVO₂). The tissue oxygen saturation (StO₂) and content (CtO₂) as well as the microvascular bed volume were derived from the haemoglobin concentration. Nonparametric tests were used to compare data within each group and among the groups and with a group of 22 matched healthy controls.

Results

The total haemoglobin concentration and [HHb] increased significantly during dialysis in patients without and with diabetes. Only in patients with diabetes, dialysis involved a [HbO₂], CtO₂ and increase but left mVO₂ unchanged. Multiple regression StO₂ analysis disclosed a significant direct correlation of StO₂ with HbO₂ and an inverse correlation with mVO₂. Dialysis increased mBF only in diabetic patients. Microvascular compliance decreased rapidly and significantly during the first hour of dialysis in both groups.

Conclusions

Our NIRS findings suggest that haemodialysis in subjects at rest brings about major changes in skeletal muscle oxygenation, blood flow, microvascular compliance and tissue metabolic rate. These changes differ in patients with and without diabetes. In all patients haemodialysis induces changes in tissue haemoglobin concentrations and microvascular compliance, whereas in patients with diabetes it alters tissue blood flow, tissue oxygenation (CtO₂, [HbO₂]) and the metabolic rate (mVO₂). In these patients the mVO₂ is correlated to the blood supply. The effects of haemodialysis on cell damage remain to be clarified. The absence of StO₂ changes is probably linked to an opposite [HbO₂] and mVO₂ pattern.

Portable optical tissue flow oximeter based on diffuse correlation spectroscopy

A portable diffuse correlation spectroscopy (DCS) flowmeter has been extended to measure both tissue blood flow and oxygenation (namely, DCS flow oximeter). For validation purposes, calf muscle blood oxygenation during cuff inflation and deflation was measured concurrently using the DCS flow oximeter and a commercial tissue oximeter. The oxygenation traces from the two measurements exhibited similar dynamic responses, and data were highly correlated (r(mean)>0.9, P<10(-5), n=10). The portable, inexpensive, and easy-to-use DCS flow oximeter holds promise for bedside monitoring of tissue blood flow and oxygenation in clinics.

Chromophore concentrations, absorption and scattering properties of human skin in-vivo

Absorption and reduced scattering coefficients of in-vivo human skin provide critical information on non-invasive skin diagnoses for aesthetic and clinical purposes. To date, very few in-vivo skin optical properties have been reported. Previously, we reported absorption and scattering properties of in-vivo skin in the wavelength range from 650 to 1000 nm using the diffusing probe in the "modified two-layer geometry". In this study, we determine the spectra of skin optical properties continuously in the range from 500 to 1000 nm. It was found that the concentration of chromophores, such as oxy-hemoglobin, deoxy-hemoglobin, and melanin, calculated based on the absorption spectra of eighteen subjects at wavelengths above and below 600 nm were distinct because of the inherent difference in the interrogation region. The scattering power, which is related to the average scatterer's size, demonstrates a clear contrast between skin phototypes, skin sites, and wavelengths. We also applied venous occlusion on forearms and found that the concentrations of oxy- and deoxy-hemoglobin as assessed at wavelengths above and below 600 nm were different. Our results suggest that diffuse reflectance techniques with the visible and near infrared light sources can be employed to investigate the hemodynamics and optical properties of upper dermis and lower dermis.

Modeling oxygenation in venous blood and skeletal muscle in response to exercise using near-infrared spectroscopy

Noninvasive, continuous measurements in vivo are commonly used to make inferences about mechanisms controlling internal and external respiration during exercise. In particular, the dynamic response of muscle oxygenation (Sm(O(2))) measured by near-infrared spectroscopy (NIRS) is assumed to be correlated to that of venous oxygen saturation (Sv(O(2))) measured invasively. However, there are situations where the dynamics of Sm(O(2)) and Sv(O(2)) do not follow the same pattern. A quantitative analysis of venous and muscle oxygenation dynamics during exercise is necessary to explain the links between different patterns observed experimentally. For this purpose, a mathematical model of oxygen transport and utilization that accounts for the relative contribution of hemoglobin (Hb) and myoglobin (Mb) to the NIRS signal was developed. This model includes changes in microvascular composition within skeletal muscle during exercise and integrates experimental data in a consistent and mechanistic manner. Three subjects (age 25.6 +/- 0.6 yr) performed square-wave moderate exercise on a cycle ergometer under normoxic and hypoxic conditions while muscle oxygenation (C(oxy)) and deoxygenation (C(deoxy)) were measured by NIRS. Under normoxia, the oxygenated Hb/Mb concentration (C(oxy)) drops rapidly at the onset of exercise and then increases monotonically. Under hypoxia, C(oxy) decreases exponentially to a steady state within approximately 2 min. In contrast, model simulations of venous oxygen concentration show an exponential decrease under both conditions due to the imbalance between oxygen delivery and consumption at the onset of exercise. Also, model simulations that distinguish the dynamic responses of oxy-and deoxygenated Hb (HbO(2), HHb) and Mb (MbO(2), HMb) concentrations (C(oxy) = HbO(2) + MbO(2); C(deoxy) = HHb + HMb) show that Hb and Mb contributions to the NIRS signal are comparable. Analysis of NIRS signal components during exercise with a mechanistic model of oxygen transport and metabolism indicates that changes in oxygenated Hb and Mb are responsible for different patterns of Sm(O(2)) and Sv(O(2)) dynamics observed under normoxia and hypoxia.

Optical imaging instrument for muscle oxygenation based on spatially resolved spectroscopy

An imaging instrument based on spatially resolved spectroscopy that enables temporal and spatial analyses of muscle oxygenation was designed. The instrument is portable and can be connected to 32 compact and separate-type optical probes. Its measurement accuracy of O(2) saturation and hemoglobin concentration was evaluated using a tissue-equivalent phantom. Imaging and multi-point measurements of tissue oxygen saturation (S(t)O(2)) in the quadriceps muscle were also performed, and dynamic changes in S(t)O(2) in response to increase in exercise intensity (within the rectus femoris region) and variation in exercise protocol (among the rectus femoris, vastus lateralis and vastus medialis) were clearly shown.

Progress of near-infrared spectroscopy and topography for brain and muscle clinical applications

This review celebrates the 30th anniversary of the first in vivo near-infrared (NIR) spectroscopy (NIRS) publication, which was authored by Professor Frans Jobsis. At first, NIRS was utilized to experimentally and clinically investigate cerebral oxygenation. Later it was applied to study muscle oxidative metabolism. Since 1993, the discovery that the functional activation of the human cerebral cortex can be explored by NIRS has added a new dimension to the research. To obtain simultaneous multiple and localized information, a further major step forward was achieved by introducing NIR imaging (NIRI) and tomography. This review reports on the progress of the NIRS and NIRI instrumentation for brain and muscle clinical applications 30 years after the discovery of in vivo NIRS. The review summarizes the measurable parameters in relation to the different techniques, the main characteristics of the prototypes under development, and the present commercially available NIRS and NIRI instrumentation. Moreover, it discusses strengths and limitations and gives an outlook into the "bright" future.

Near-infrared spectroscopy for evaluation of peripheral vascular disease. A systematic review of literature

OBJECTIVES

To assess near-infrared spectroscopy (NIRS) as a method for the diagnosis and evaluation of peripheral vascular disease.

SEARCH STRATEGY

MEDLINE and CENTRAL were searched with a search protocol presented below. Handsearching through reference lists of the retrieved articles and reviews was conducted.

MAIN RESULTS

224 and 57 abstracts from MEDLINE and CENTRAL respectively were retrieved from which 21 studies were selected. NIRS was evaluated for the diagnosis and severity evaluation in patients with peripheral vascular disease. Its parameters were shown to reflect the clinical status of patients, with good correlation to existing methods.

CONCLUSIONS

Currently NIRS technology can serve as an adjunct method for the diagnosis and evaluation of patients with peripheral vascular disease.

Regional Differences of Hemodynamics and Oxygenation in the Human Calf Muscle Detected with Near-Infrared Spectrophotometry

PURPOSE

Measurements in muscle tissue are often performed at a selected single location over the muscle of interest. The hypothesis is that the values obtained reflect the status within the entire muscle or muscle group. This, however, may not be the case. The study was performed to investigate whether this hypothesis is true for hemodynamics and oxygenation in the healthy human calf muscle at rest.

MATERIALS AND METHODS

Hemoglobin flow, blood flow, oxygen consumption, and venous hemoglobin oxygen saturation were mapped at 22 locations in 30 legs of 15 healthy subjects (nine women, six men aged 26-37 years) simultaneously by using frequency-domain near-infrared spectrophotometry with a specially designed probe during venous occlusion.

RESULTS

For all parameters, spatial heterogeneity was found between subjects and within individual legs. All parameters were highly significantly different when comparing proximal and distal regions. Differences were also found between medial and lateral regions. The global mean values (+/-standard deviation) over all measurements were as follows: hemoglobin flow, 1.27 micromol per 100 mL/min +/- 0.88; blood flow, 0.56 mL per 100 g/min +/- 0.38; oxygen consumption, 0.016 mL per 100 g/min +/- 0.011; and venous oxygen saturation, 77.6% +/- 5.9. The thickness of the overlying adipose tissue had an influence on the measurements and must be considered.

CONCLUSION

Highly significant spatial heterogeneity of hemodynamics and oxygenation was found in the healthy human calf muscle.

Dual gradient-echo MRI of post-contraction changes in skeletal muscle blood volume and oxygenation

Analysis of post-contraction MRI signal intensity (SI) transients may allow noninvasive studies of microvascular reactivity and blood oxygenation recovery. The purpose of this study was to determine the physiological basis for post-contraction changes in short-echo (6 ms) and long-echo (46 ms) gradient-echo (GRE) MRI signals (S(6) and S(46), respectively). Six healthy subjects were studied with the use of dual GRE MRI and near-infrared spectroscopy (NIRS). S(6), S(46), total hemoglobin concentration ([THb]), and oxyhemoglobin saturation (%HbO(2)) were measured before, during, and after 2 and 8 s dorsiflexion maximal voluntary contractions, and 5 min of proximal arterial occlusion. The changes in S(6) and [THb] after the 2-s contractions were similar to those following 8-s contractions, but changes in %HbO(2) and S(46) were greater following 8-s contractions than after the 2-s contractions. [THb] and S(6) did not change during and following 5 min of arterial occlusion, but %HbO(2) and S(46) were both significantly depressed at similar occlusion durations. Also, distance measures indicated similarity between S(6) and [THb] and between S(46) and %HbO(2). We conclude that following brief human skeletal muscle contractions, changes in S(6) primarily reflect changes in blood volume and changes in S(46) primarily reflect changes in blood oxygenation.

A novel method to measure regional muscle blood flow continuously using NIRS kinetics information

BACKGROUND

This article introduces a novel method to continuously monitor regional muscle blood flow by using Near Infrared Spectroscopy (NIRS). We demonstrate the feasibility of the new method in two ways: (1) by applying this new method of determining blood flow to experimental NIRS data during exercise and ischemia; and, (2) by simulating muscle oxygenation and blood flow values using these newly developed equations during recovery from exercise and ischemia.

METHODS

Deoxy (Hb) and oxyhemoglobin (HbO2), located in the blood of the skeletal muscle, carry two internal relationships between blood flow and oxygen consumption. One is a mass transfer principle and the other describes a relationship between oxygen consumption and Hb kinetics in a two-compartment model. To monitor blood flow continuously, we transfer these two relationships into two equations and calculate the blood flow with the differential information of HbO2 and Hb. In addition, these equations are used to simulate the relationship between blood flow and reoxygenation kinetics after cuff ischemia and a light exercise. Nine healthy subjects volunteered for the cuff ischemia, light arm exercise and arm exercise with cuff ischemia for the experimental study.

RESULTS

Analysis of experimental data of both cuff ischemia and light exercise using the new equations show greater blood flow (four to six times more than resting values) during recovery, agreeing with previous findings. Further, the simulation and experimental studies of cuff ischemia and light exercise agree with each other.

CONCLUSION

We demonstrate the accuracy of this new method by showing that the blood flow obtained from the method agrees with previous data as well as with simulated data. We conclude that this novel continuous blood flow monitoring method can provide blood flow information non-invasively with NIRS.

Heterogeneous oxygenation in nonexercising triceps surae muscle during contralateral isometric exercise

To test whether changes in oxygenation of a resting skeletal muscle, evoked by a static contraction in a contralateral muscle, is uniform within a given skeletal muscle, we used near-infrared spectroscopy (NIRS). Seven subjects performed 2 min static knee extension exercise at 30% of maximal voluntary contraction. Changes in oxygenated hemoglobin (HbO(2)) were monitored using multiple-channel NIRS (40 channels, 13 sources and 12 detectors) attached on the contralateral nonexercising triceps surae muscle. Changes in HbO(2) were expressed as a percentage of total labile signals. To characterize the distribution of changes in HbO(2), channels were compared between their positions on the triceps surae muscle, and represented as 'proximal versus distal' and 'lateral versus medial' portions. During static muscle contraction, the averaged changes in HbO(2) of all channels were correlated with those in calf blood flow (plethysmography; R (2)=0.188, P<0.05) and with calf vascular conductance (R (2)=0.146, P<0.05). HbO(2) did not differ significantly between the lateral and medial portions of the triceps surae muscle. In contrast, the decrease of HbO(2) in the proximal portion of the muscle was greater than that of the distal portion (P<0.05). These results indicate that the changes in oxygenation of a resting muscle, evoked by static contraction of the contralateral muscle, are heterogeneous.

Near-infrared spectroscopy and transcutaneous oxygen pressure during exercise to detect arterial ischemia at the buttock level: Comparison with arteriography

BACKGROUND

Noninvasive tests are required to detect (in both male and female subjects and side by side) arteries toward the hypogastric circulation that are likely to present significant lesions as a cause of buttock claudication.

METHODS

We compared the accuracy of near-infrared spectroscopy (NIRS) and transcutaneous oxygen pressure (TCP o 2 ) on both buttocks during walking tests to detect lesions on the arteries toward the hypogastric circulation. NIRS was considered abnormal if recovery time to pre-exercise values was greater than 240 seconds for tissue oxygen saturation (absent data being coded 0), and TCP o 2 was coded abnormal if the minimal value of buttock changes minus chest changes was lower than -15 mm Hg. The study was conducted in a university hospital; there were 30 ambulatory patients with stage 2 claudication of the Fontaine classification.

RESULTS

Angiography showed 36 abnormal (stenosis > 75%) and 24 normal arterial axes toward the buttocks circulation. NIRS and TCP o 2 provided respectively 55% (range, 41.6% to 67.9%) and 82% (range, 69.6% to 90.5%) accuracy (95% confidence interval) to predict the presence of arteriographically proven lesions; P < .05.

CONCLUSIONS

Using available cut-off points proposed in the literature, NIRS showed a lower diagnostic accuracy than TCP o 2 for the prediction of lesions on the arterial tree to the hypogastric circulation. NIRS is a recent technique as compared with TCP o 2 , and its diagnostic accuracy might improve in the future. Currently, one should carefully weigh the advantages and limits of NIRS and TCP o 2 when a choice is to be made between them to monitor exercise-induced changes resulting from lower limb arterial disease at the proximal level.

Non-PET functional imaging techniques: optical

The strong and steady development of diffuse optical spectroscopy and tomography as new biomedical optics technologies promises to bring these optical techniques into clinical practice. This article provides a brief review of the light-tissue interaction, the instrumentation, and the theory relevant to this field. This is followed by a survey of the three main applications: brain imaging, muscle imaging, and breast imaging. Lastly, the future outlook of the technology is presented, highlighting the new promises based on recent breakthroughs.

Time-dependent blood flow and oxygenation in human skeletal muscles measured with noninvasive near-infrared diffuse optical spectroscopies

We have employed near-infrared optical methods to measure noninvasively the dynamics of muscle blood flow and oxygen saturation (StO2) during cuff occlusion and plantar flexion exercise. Relative muscle oxygen consumption (rVO2) was also computed from these data. Diffuse correlation spectroscopy provides information about blood flow, and diffuse reflectance spectroscopy provides information about blood oxygenation. Ten healthy subjects and one patient with peripheral arterial disease (PAD) were studied during 3-min arterial cuff occlusion of arm and leg, and during 1-min plantar flexion exercise. Signals from different layers (cutaneous tissues and muscles) during cuff occlusion were differentiated, revealing strong hemodynamic responses from muscle layers. During exercise in healthy legs, the observed approximately 4.7 fold increase in relative blood flow (rBF) was significantly lower than the corresponding increase in rVO2 (approximately 7 fold). The magnitudes of rBF and rVO2 during exercise in the PAD patient were approximately 1/2 of the healthy controls, and the StO2 recovery time was twice that of the controls. The hybrid instrument improves upon current technologies for measuring muscle responses by simultaneously measuring rBF and StO2. The instrument thus provides a method for evaluation of microcirculation and muscle metabolism in patients with vascular diseases.

Spatial distribution of vastus lateralis blood flow and oxyhemoglobin saturation measured at the end of isometric quadriceps contraction by multichannel near-infrared spectroscopy

Muscle blood flow (MBF) and muscle oxygen saturation (SmO(2)) were measured at eight locations (four proximal, four distal) over a 4 x 8 cm(2) area of the vastus lateralis at rest and immediately after isometric, maximal quadriceps contraction using multichannel, frequency-domain, near-infrared spectroscopy. A venous occlusion was applied 20 s before the end of the exercise, so that the venous-occlusion-induced increase in total hemoglobin was recorded without any delay after the end of the exercise. Therefore, we were able to investigate the relationship between the exercise-induced changes in vastus lateralis MBF and SmO(2). After exercise, MBF increased significantly at each measured location. Comparing the MBF values measured at the end of exercise in the proximal and distal regions, we observed that only one proximal region had a significantly higher MBF than the corresponding distal one. The maximum desaturation measured during exercise was positively correlated with the postexercise to pre-exercise MBF ratio in both the proximal (P=0.016) and distal (P=0.0065) regions. These data confirm that frequency-domain tissue oximeters are noninvasive, powerful tools to investigate the spatial and temporal features of muscle blood flow and oxygenation, with potential applications in areas of pathophysiology.

Mapping of calf muscle oxygenation and haemoglobin content during dynamic plantar flexion exercise by multi-channel time-resolved near-infrared spectroscopy

A compact and fast multi-channel time-resolved near-infrared spectroscopy system for tissue oximetry was developed. It employs semiconductor laser and fibre optics for delivery of optical signals. Photons are collected by eight 1 mm fibres and detected by a multianode photomultiplier. A time-correlated single photon counting board is used for the parallel acquisition of time-resolved reflectance curves. Estimate of the reduced scattering coefficient is achieved by fitting with a standard model of diffusion theory, while the modified Lambert-Beer law is used to assess the absorption coefficient. In vivo measurements were performed on five healthy volunteers to monitor spatial changes in calf muscle (medial and lateral gastrocnemius; MG, LG) oxygen saturation (SmO2) and total haemoglobin concentration (tHb) during dynamic plantar flexion exercise performed at 50% of the maximal voluntary contraction. At rest SmO2 was 73.0 +/- 0.9 and 70.5 +/- 1.7% in MG and LG, respectively (P = 0.045). At the end of the exercise, SmO2 decreased (69.1 +/- 1.8 and 63.8 +/- 2.1% in MG and LG, respectively; P < 0.01). The LG desaturation was greater than the MG desaturation (P < 0.02). These results strengthen the role of time-resolved near-infrared spectroscopy as a powerful tool for investigating the spatial and temporal features of muscle SmO2 and tHb.