Tissue (muscle) oxygen saturation (StO2): A new measure of symptomatic lower-extremity arterial disease

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.

Hyperoxia impairs induced pluripotent stem cell-derived endothelial cells and drives an atherosclerosis-like transcriptional phenotype

Background

Induced pluripotent stem cells (iPSCs) directed to endothelial identity (iPSC-ECs) are emerging as a potent tool for regenerative medicine in vascular disease. However, iPSC-ECs lose expression of key identity markers under standard in vitro conditions, limiting their clinical applications.

Methods

To model physiological in vivo conditions, we examined the bioenergetics, presence of key cell markers, and proliferative and angiogenic capacity in iPSC-ECs at late and early passage under hyperoxic (21%) and physiological (4%) oxygen concentrations.

Results

Physoxia resulted in relative preservation of mitochondrial bioenergetic activity, as well as CD144 expression in late passage iPSC-ECs, but not proliferative capacity or tube formation. Single cell RNA sequencing (scRNA-seq) revealed that late passage hyperoxic iPSC-ECs develop an endothelial-to-mesenchymal phenotype. Comparing scRNA-seq data from iPSC-ECs and from atherosclerotic ECs revealed overlap of their transcriptional phenotypes.

Conclusions

Taken together, our studies demonstrate that physiological 4% oxygen culture conditions were sufficient to improve mitochondrial function in high passage cells, but alone was insufficient to preserve angiogenic capacity. Furthermore, late passage cells under typical conditions take on an endothelial-to-mesenchymal phenotype with similarities to ECs found in atherosclerosis.

Wearable Prophylaxis Tool for AI-Driven Identification of Early Warning Patterns of Pressure Ulcers

As today's society ages, age-related diseases become more frequent. One very common but yet preventable disease is the development of pressure ulcers (PUs). PUs can occur if tissue is exposed to a long-lasting pressure load, e.g., lying on tissue without turning. The cure of PUs requires intensive care, especially for the elderly or people with preexisting conditions whose tissue needs longer healing times. The consequences are heavy suffering for the patient and extreme costs for the health care system. To avoid these consequences, our objective is to develop a pressure ulcer prophylaxis device. For that, we built a new sensor system able to monitor the pressure load and tissue vital signs in immediate local proximity at patient's predilection sites. In the clinical study, we found several indicators showing correlations between tissue perfusion and the risk of PU development, including strongly reduced SpO2 levels in body tissue prior to a diagnosed PU. Finally, we propose a prophylaxis system that allows for the prediction of PU developments in early stages before they become visible. This work is the first step in generating an effective system to warn patients or caregivers about developing PUs and taking appropriate preventative measures. Widespread application could reduce patient suffering and lead to substantial cost savings.

Unraveling the pathophysiology of lower-limb postthrombotic syndrome in adolescents: a proof-of-concept study

A better understanding of the pathophysiology of pediatric postthrombotic syndrome (PTS) is needed to develop strategies to treat this condition. We investigated calf pump function, exercise capacity, balance in power output, and changes in limb muscle oxygen saturation (SmO2) and fluid content during exercise in 10 pediatric patients with unilateral lower-limb PTS, and in age- and sex-matched controls (1:1-1:2 ratio). Outcomes were investigated using bioimpedance spectroscopy, torque-sensing pedals, and near-infrared spectroscopy during incremental- and constant-load cycling tests. The median age at participation was 17 years (25th-75th percentile, 15-18 years); 68% of participants were females. The median CAPTSure score in the affected leg of affected participants was 35 points (25th-75th percentile, 24-46 points), indicating moderate/severe PTS; 20% of patients had a history of central venous catheter-related thrombosis. Increasing PTS severity was associated with higher calf pump venous volume and higher ejection volume, leading to compensated calf pump performance. We found no evidence of PTS impact on exercise capacity. Leg contribution to power output was similar in affected and unaffected legs. However, the PTS-affected legs showed lower SmO2 during active cycling and recovery with increasing PTS severity, indicating impaired microvascular function in the muscle. These findings suggest that PTS severity is associated with impaired blood flow, presumably from elevated venous pressure during and after exercise. The fact that microvascular function is impaired in young patients with PTS underscores the relevance of developing strategies to mitigate the effects of this chronic vascular disease to minimize its deleterious effects as children grow older.

Oxygen Uptake and Bilaterally Measured Vastus Lateralis Muscle Oxygen Desaturation Kinetics in Well-Trained Endurance Cyclists

The aim of the present study was to compare and analyse the relationships between pulmonary oxygen uptake and vastus lateralis (VL) muscle oxygen desaturation kinetics measured bilaterally with Moxy NIRS sensors in trained endurance athletes. To this end, 18 trained athletes (age: 42.4 ± 7.2 years, height: 1.837 ± 0.053 m, body mass: 82.4 ± 5.7 kg) visited the laboratory on two consecutive days. On the first day, an incremental test was performed to determine the power values for the gas exchange threshold, the ventilatory threshold (VT), and V̇O_2max levels from pulmonary ventilation. On the second day, the athletes performed a constant work rate (CWR) test at the power corresponding to the VT. During the CWR test, the pulmonary ventilation characteristics, left and right VL muscle O₂ desaturation (DeSmO₂), and pedalling power were continuously recorded, and the average signal of both legs' DeSmO₂ was computed. Statistical significance was set at p ≤ 0.05. The relative response amplitudes of the primary and slow components of VL desaturation and pulmonary oxygen uptake kinetics did not differ, and the primary amplitude of muscle desaturation kinetics was strongly associated with the initial response rate of oxygen uptake. Compared with pulmonary O₂ kinetics, the primary response time of the muscle desaturation kinetics was shorter, and the slow component started earlier. There was good agreement between the time delays of the slow components describing global and local metabolic processes. Nevertheless, there was a low level of agreement between contralateral desaturation kinetic variables. The averaged DeSmO₂ signal of the two sides of the body represented the oxygen kinetics more precisely than the right- or left-leg signals separately.

Moderate dose of dietary nitrate improves skeletal muscle microvascular function in patients with peripheral artery disease

Peripheral artery disease (PAD) is an atherosclerotic disease characterized by compromised lower-extremity blood flow that impairs walking ability. We showed that a moderate dose of dietary nitrate in the form of beetroot juice (BRJ, 0.11 mmol/kg) can improve macrovascular function and maximal walking distance in patients with PAD. However, its impacts on the microcirculation and autonomic nervous system have not been examined. Therefore, we investigated the impacts of this dose of dietary nitrate on skeletal muscle microvascular function and autonomic nervous system function and further related these measurements to 6-min walking distance, pain-free walking distance, and exercise recovery in patients with PAD. Patients with PAD (n = 10) ingested either BRJ or placebo in a randomized crossover design. Heart rate variability, skeletal muscle microvascular function, and 6-min walking distance were performed pre- and post-BRJ and placebo. There were significant group × time interactions (P < 0.05) for skeletal muscle microvascular function, 6-min walking distance, and exercise recovery, but no changes (P > 0.05) in heart rate variability or pain-free walking distance were noted. The BRJ group demonstrated improved skeletal muscle microvascular function (∆ 22.1 ± 7.5 %·min-1), longer 6-min walking distance (Δ 37.5 ± 9.1 m), and faster recovery post-exercise (Δ -15.3 ± 4.2 s). Furthermore, changes in skeletal muscle microvascular function were positively associated with changes in 6-min walking distance (r = 0.5) and pain-free walking distance (r = 0.6). These results suggest that a moderate dose of dietary nitrate may support microvascular function, which is related to improvements in walking distance and claudication in patients with PAD.

Endovascular Revascularization of Isolated Internal Iliac Artery for symptomatic occlusive atherosclerotic disease is a viable and underutilized option for patients with gluteal muscle claudication

Often confused with pseudoclaudication, gluteal muscle claudication is a difficult condition to diagnose and treat. We present the case of a 67-year-old man with a history of back and buttock claudication. He had undergone lumbosacral decompression with no relief of buttock claudication. Computed tomography angiography of the abdomen and pelvis showed occlusion of the bilateral internal iliac arteries. Exercise transcutaneous oxygen pressure measurements obtained on referral to our institution revealed a significant decrease. He underwent successful recanalization and stenting of the bilateral hypogastric arteries with complete resolution of his symptoms. We also reviewed the reported data to highlight the trend in the management of patients with this condition.

Incidence, predictors and vascular sequelae of distal limb ischemia in minimally invasive cardiac surgery with femoral artery cannulation: an observational cohort study

Literature regarding monitoring and consequences of distal limb ischemia due to femoral artery cannulation for Minimally Invasive Cardiac Surgery (MICS) remains limited. The primary objective was to determine its incidence, defined as a ≥ 15% difference in regional Oxygen Saturation (rSO₂) lasting ≥ four consecutive minutes between the cannulated and non-cannulated limb. The secondary objectives included: determination of distal limb ischemia, defined as a Tissue Oxygenation Index (TOI) < 50% in the cannulated limb, identification of predictors for distal limb ischemia, determination of a possible association of NIRS-diagnosed ischemia with acute kidney injury, and the need for vascular surgery up to six months after cardiac surgery. A prospective, observational cohort study with blinded rSO₂-measurements to prevent intraoperative clinical decision-making. A single-center, community-hospital, clinical study. All consecutive patients ≥ 18 years old, and scheduled for predefined MICS. Patients underwent MICS with bilateral calf muscle rSO₂-measurements conducted by Near-Infrared Spectroscopy (NIRS). In total 75/280 patients (26.79%) experienced distal limb ischemia according to the primary objective, while 18/280 patients (6.42%) experienced distal limb ischemia according to the secondary objective. Multivariate logistic regression showed younger age to be an independent predictor for distal limb ischemia (p = 0.003). None of the patients who suffered intraoperative ischemia required vascular surgery within the follow-up period. The incidence of NIRS-diagnosed ischemia varied from 6.4% to 26.8% depending on the used criteria. Short and long-term vascular sequelae, however, are limited and not intraoperative ischemia related. The added value of intraoperative distal limb NIRS monitoring for vascular reasons seems limited. Future research on femoral artery cannulation in MICS should shift focus to other outcome parameters such as acute kidney injury, postoperative pain or paresthesias.

Effects of Lower Limb Revascularization on the Microcirculation of the Foot: A Retrospective Cohort Study

Background: Current assessment standards in chronic limb-threatening ischemia (CLTI) focus on macrovascular function while neglecting the microcirculation. Multispectral near-infrared spectroscopy (NIRS) provides hemodynamic characteristics of the microcirculation (i.e., capillaries) and may be a powerful tool for monitoring CLTI and preventing extremity loss. The aims of this study were to (1) investigate the effects of lower limb revascularization on the microcirculation and (2) determine if macrovascular and microvascular assessments correlate. Methods: An observational, retrospective cohort study of 38 endovascular interventions in 30 CLTI subjects was analyzed pre- and post-intervention for arterial Doppler acceleration times (AcT; macrovascular) and NIRS metrics (microvascular). Pre-intervention ankle-brachial index (ABI) was also analyzed. Results: AcT significantly decreased (p = 0.009) while oxyhemoglobin (HbO) significantly increased (p < 0.04) after endovascular intervention, indicating treatment efficacy. However, macrovascular measurements (ABI, AcT) and NIRS metrics of oxygenation and perfusion did not correlate (p > 0.06, r2 < 0.15, n = 23) indicating that macro- and microvascular assessment are not congruent. Conclusion: These findings suggest that macrovascular and microvascular assessments can determine interventional efficacy in their corresponding vasculature. Their lack of correlation, however, suggests the need for simultaneous assessment as independent use may cause diagnostic information to be missed.

Impaired microcirculatory function, mitochondrial respiration, and oxygen utilization in skeletal muscle of claudicating patients with peripheral artery disease

Peripheral artery disease (PAD) is an atherosclerotic disease that impairs blood flow and muscle function in the lower limbs. A skeletal muscle myopathy characterized by mitochondrial dysfunction and oxidative damage is present in PAD; however, the underlying mechanisms are not well established. We investigated the impact of chronic ischemia on skeletal muscle microcirculatory function and its association with leg skeletal muscle mitochondrial function and oxygen delivery and utilization capacity in PAD. Gastrocnemius samples and arterioles were harvested from patients with PAD (n = 10) and age-matched controls (Con, n = 11). Endothelium-dependent and independent vasodilation was assessed in response to flow (30 μL·min-1), acetylcholine, and sodium nitroprusside (SNP). Skeletal muscle mitochondrial respiration was quantified by high-resolution respirometry, microvascular oxygen delivery, and utilization capacity (tissue oxygenation index, TOI) were assessed by near-infrared spectroscopy. Vasodilation was attenuated in PAD (P < 0.05) in response to acetylcholine (Con: 71.1 ± 11.1%, PAD: 45.7 ± 18.1%) and flow (Con: 46.6 ± 20.1%, PAD: 29.3 ± 10.5%) but not SNP (P = 0.30). Complex I + II state 3 respiration (P < 0.01) and TOI recovery rate were impaired in PAD (P < 0.05). Both flow and acetylcholine-mediated vasodilation were positively associated with complex I + II state 3 respiration (r = 0.5 and r = 0.5, respectively, P < 0.05). Flow-mediated vasodilation and complex I + II state 3 respiration were positively associated with TOI recovery rate (r = 0.8 and r = 0.7, respectively, P < 0.05). These findings suggest that chronic ischemia attenuates skeletal muscle arteriole endothelial function, which may be a key mediator for mitochondrial and microcirculatory dysfunction in the PAD leg skeletal muscle. Targeting microvascular dysfunction may be an effective strategy to prevent and/or reverse disease progression in PAD.NEW & NOTEWORTHY Ex vivo skeletal muscle arteriole endothelial function is impaired in claudicating patients with PAD, and this is associated with attenuated skeletal muscle mitochondrial respiration. In vivo skeletal muscle oxygen delivery and utilization capacity is compromised in PAD, and this may be due to microcirculatory and mitochondrial dysfunction. These results suggest that targeting skeletal muscle arteriole function may lead to improvements in skeletal muscle mitochondrial respiration and oxygen delivery and utilization capacity in claudicating patients with PAD.

Aging alters gastrocnemius muscle hemoglobin oxygen saturation (StO2) characteristics in healthy individuals

PURPOSE

Functional limitations during exercise from alterations in the balance of oxygen supply and demand-as reported by lower tissue oxygen saturation and longer recovery time-are well documented in clinical populations. We aimed to assess changes in skeletal muscle hemoglobin oxygen saturation (StO₂) characteristics during exercise as a result of aging in otherwise healthy individuals.

METHODS

We recruited healthy male and female participants (n = 101) from three age ranges-young (18-39 years), middle age (40-65 years), and older (> 65 years)-to complete exercise tests commonly used in clinical populations. Using near-infrared spectroscopy (NIRS) we assessed StO₂ in the medial gastrocnemius during the Gardner Treadmill Protocol and 6 min walk test (6MWT).

RESULTS

Minimum StO₂ (%) during the treadmill test was significantly lower for both middle-age (36.1 ± 20.6) and older (27.3 ± 19.4) participants compared to young (46.8 ± 14.8) (p < 0.05 and p < 0.01 respectively), and recovery time (minutes) was significantly prolonged (young = 0.22 ± 0.34; middle age = 0.66 ± 0.52; older = 1.04 ± 1.00) (p < 0.001 for both middle age and older compared to young). Similar results were shown during the 6MWT, as minimum StO₂ (%) was lower in middle-age (41.7 ± 17.2) and older (40.0 ± 25.9) participants compared to young (53.6 ± 14.5) (p < 0.05), and recovery times (minutes) were prolonged (young: 0.11 ± 0.17; middle age: 0.46 ± 0.42; older: 0.93 ± 0.43) (p < 0.001 for both middle age and older compared to young). Simple linear regression analyses demonstrated that age predicted treadmill recovery and 6MWT recovery.

CONCLUSION

Our study provides evidence that aging, even in otherwise healthy individuals, negatively impacts muscle StO₂ characteristics. In older individuals, working muscle tissue may reach lower oxygen saturation during exercise and take longer to return to baseline oxygen saturation post-exercise.

Development and Evaluation of a Remote Patient Monitoring System in Autologous Breast Reconstruction

Flap monitoring after a deep inferior epigastric perforator flap breast reconstruction is crucial to detect complications in time. A novel and innovative wireless device has been developed and tested in a feasibility study. This study describes our experience with remote patient monitoring via this device in postoperative monitoring of deep inferior epigastric perforator flaps.

Association Between Daily Steps at Moderate Cadence and Vascular Outcomes in Patients With Claudication

PURPOSE

We determined whether patients with peripheral artery disease (PAD) and claudication grouped according to tertiles of community-based daily steps taken at a moderate cadence had differences in vascular function and biomarkers and whether group differences in vascular function and biomarkers persisted after adjusting for demographic variables, comorbid conditions, and severity of PAD.

METHODS

Two hundred sixty-three patients were evaluated for 1 wk on steps taken at a moderate cadence (exceeding 60 steps/min), and patients were placed into low (group 1), intermediate (group 2), and high (group 3) tertiles.

RESULTS

Ankle/brachial index (ABI) at 1 min after exercise (mean ± SD) was significantly higher in groups 2 and 3 than in group 1 in unadjusted (P < .01) and adjusted (P < .01) analyses (group 1: 0.34 ± 0.25; group 2: 0.38 ± 0.27; and group 3: 0.44 ± 0.28). Exercise time to reach the minimum calf muscle oxygen saturation (StO2) value during treadmill exercise was significantly longer in groups 2 and 3 than in group 1 in unadjusted (P < .01) and adjusted (P < .01) analyses (group 1: 127 ± 127 sec; group 2: 251 ± 266 sec; and group 3: 310 ± 323 sec). Fibrinogen was significantly lower in group 3 than in group 1 in unadjusted (P = .02) and adjusted (P = .05) analyses (group 1: 3.5 ± 1.2 g/L; group 2: 3.6 ± 1.5 g/L; and group 3: 3.0 ± 1.1 g/L).

CONCLUSIONS

Compared with patients with claudication in the lowest tertile of community-based daily steps taken at a moderate cadence, patients in the second and third tertiles had better calf muscle StO2 and ABI values during and immediately after exercise. Second, the most active group had lower fibrinogen levels than the least active group.

Evaluation of functional capacity and muscle metabolism in individuals with peripheral arterial disease with and without diabetes

OBJECTIVE

Peripheral arterial disease (PAD) is characterized by intermittent claudication, which interferes with walking and leads to worsening of functional capacity. This mechanism has not been clearly defined in PAD. Thus, the aim of our study was to identify the muscular metabolism and vascular function variables using near-infrared spectroscopy (NIRS) and their possible associations with functional capacity in individuals with PAD and secondly to verify the differences in these variables between persons with PAD and diabetes mellitus (DM) and those with PAD without DM.

METHODS

A total of 39 participants with intermittent claudication were enrolled, 14 of whom had DM. They were assessed for functional capacity by the total distance covered in the treadmill test with the speed and grade constant and for muscle function and metabolism using near-infrared spectroscopy at rest and during the treadmill test. The Spearman correlation coefficient was computed to assess the presence of an association between the variables, and multiple linear regression analysis was performed, considering the total test distance as the dependent variable. The assessment between groups was performed using the independent t test or Mann-Whitney U test.

RESULTS

The near-infrared spectroscopy variables related to tissue oxygen saturation in the test recovery phase were correlated with the functional performance during the treadmill test. Thus, those with a longer or slower recovery time and those with greater tissue deoxygenation had walked a shorter distance. A significant difference (P = .049) was noted between those with PAD stratified by DM in the reoxygenation time required for an occlusion.

CONCLUSIONS

These findings reinforce the hypothesis that peripheral factors related to vascular function and muscular metabolism can affect the walking capacity of persons with PAD and that microvascular dysfunction is more prevalent among those with PAD and DM.

Ankle-brachial index to monitor limb perfusion in patients with femoral venoarterial extracorporeal membrane oxygenation

BACKGROUND

Limb ischemia is a major complication of femoral venoarterial extracorporeal membrane oxygenation (VA-ECMO). Use of ankle-brachial index (ABI) to monitor limb perfusion in VA-ECMO has not been described. We report our experience monitoring femoral VA-ECMO patients with serial ABI and the relationships between ABI and near infrared spectroscopy (NIRS).

METHODS

This is a retrospective single-center review of consecutive adult patients placed on femoral VA-ECMO between January 2019 and October 2019. Data were collected on patients with paired ABI and NIRS values. Relationships between NIRS and ABI of the cannulated (E-NIRS and E-ABI) and non-cannulated legs (N-NIRS and N-ABI) along with the difference between legs (d-NIRS and d-ABI) were determined using Pearson correlation.

RESULTS

Overall, 22 patients (mean age 56.5 ± 14.0 years, 72.7% male) were assessed with 295 E-ABI and E-NIRS measurements, and 273 N-ABI and N-NIRS measurements. Mean duration of ECMO support was 129.8 ± 78.3 h. ECMO-mortality was 13.6% and in-hospital mortality was 45.5%. N-ABI and N-NIRS were significantly higher than their ECMO counterparts (ABI mean difference 0.16, 95% confidence interval [CI]: 0.13-0.19, p < .0001; NIRS mean difference 2.51, 95% CI: 1.48-3.54, p < .0001). There was no correlation between E-ABI versus E-NIRS (r = .032, p = .59), N-ABI versus N-NIRS (r = .097, p = .11), or d-NIRS versus d-ABI (r = .11, p = .069).

CONCLUSION

ABI is a quantitative metric that may be used to monitor limb perfusion and supplement clinical exams to identify limb ischemia in femorally cannulated VA-ECMO patients. More studies are needed to characterize the significance of ABI in femoral VA-ECMO and its value in identifying limb ischemia in this patient population.

The use of near-infrared spectroscopy in the diagnosis of peripheral artery disease: A systematic review

BACKGROUND

Peripheral arterial disease is a stenosis or occlusion of peripheral arteries that results in compromised blood flow and muscle ischemia. The available diagnostic methods are mostly used to measure and visualize blood flow and are not useful in the evaluation of perfusion, especially in diabetic patients, which is now considered to be a research priority by most of the vascular societies around the world as this is still a relatively poorly studied phenomenon.

OBJECTIVE

The aim of this review is to explore the clinical significance of muscle tissue oxygenation monitoring in lower-extremity peripheral artery disease diagnosis using the near-infrared spectroscopy method.

METHODS

A systematic search in PubMed, CINAHL, and Cochrane databases was performed to identify clinical near-infrared spectroscopy (NIRS) studies in English and Russian, published until September 2019, involving muscle tissue oxygenation in peripheral arterial disease (PAD). The manuscripts were reviewed by two researchers independently and scored on the quality of the research using MINORS criteria.

RESULTS

After screening 443 manuscripts, 23 studies (n = 1580) were included. NIRS-evaluated recovery time seems to be more accurate than ankle-brachial index in diabetic patients to differentiate between moderate and severe claudication. Consistent findings across all the included studies showed that both the oxygenation and deoxygenation rates as well as the recovery times varied from patient to patient and therefore were not suitable for standardization.

CONCLUSIONS

The clinical relevance of routine use of NIRS to diagnose PAD is unproven; therefore, its use is not currently part of standard-of-care for patients with PAD since the absolute values seem to vary significantly, depending on the outside conditions. More data need to be provided on the possible use of NIRS monitoring intraoperatively where the conditions can be more controlled.

Effect of revascularisation on lower extremity muscle function in combined type 2 diabetes and critical limb threatening ischemia

BACKGROUND

Critical limb-threatening ischemia (CLTI) and type 2 diabetes (T2D) frequently co-exist and often with less favourable outcome after revascularisation. The objective was to evaluate the effects of revascularisation on muscle function, perfusion and mitochondrial respiration in patients with combined CLTI and T2D.

METHODS

A prospective translational observational study. Two groups of patients facing unilateral peripheral revascularisation was included: Patients suffering from combined disease with CLTI+T2D (n= 14) and patients suffering from CLTI (n= 15). During pedal exercise testing, calf muscle perfusion was monitored with near-infrared spectroscopy (NIRS) and leg arterial volume flow in the common femoral artery with duplex ultrasound. Calf muscle biopsy and subsequent assessment of mitochondrial respiratory capacity on isolated muscle fibres was performed. Tests was performed before and six weeks after revascularisation.

RESULTS

After revascularisation, patients CLTI+T2D improved in muscle force from 8.48 kg (CI: 7.49-9.46) to 13.11 kg (CI: 11.58-14.63), (P<.001). Conversely, muscle force in patients suffering from nondiabetic CLTI decreased from 10.03 kg (CI: 9.1-10.96) to 9.73 kg (CI: 8.77- 10.69), (P=0.042). Muscle oxygenation during exercise improved more in the CLTI+T2D group 6.36 AUC (Area Under Curve), ((μM/kg)s) (CI: 5.71-7.01) compared to 2.11 ((μM/kg)s) (CI:1.38-2.83) in the CLTI group (P=.002). No improvement or difference between groups regarding mitochondrial function was detected.

CONCLUSIONS

Patients with combined CLTI+T2D, had an unsuspected better effect of revascularisation compared to patients with non-diabetic CLTI, in terms of increased muscle force (MVC) and improved muscle perfusion. Further studies are needed to elucidate the apparent interaction of the CLTI and T2D syndromes.

Association between calf muscle oxygen saturation with ambulatory function and quality of life in symptomatic patients with peripheral artery disease

OBJECTIVE

The objective of this study was to determine whether calf muscle hemoglobin oxygen saturation (Sto₂) obtained during a standardized treadmill test is associated with ambulatory function and health-related quality of life (HRQoL) in patients with symptomatic peripheral artery disease (PAD). We hypothesized that a rapid decline in calf muscle Sto₂ during walking is associated with impaired ambulatory function and HRQoL and that these associations are independent of ankle-brachial index (ABI).

METHODS

Calf muscle Sto₂, peak walking time, and claudication onset time were obtained during a treadmill test in 151 symptomatic men and women with PAD. Patients were further characterized by demographic variables, comorbid conditions, cardiovascular risk factors, ABI, 6-minute walk distance, daily ambulatory activity, Walking Impairment Questionnaire (WIQ) score, and Medical Outcomes Study 36-Item Short Form Health Survey physical function score to assess HRQoL.

RESULTS

The median calf muscle Sto₂ value at rest was 52%, which declined to 22% after only 1 minute of walking during the treadmill test and reached a minimum value of 9% after a median time of 87 seconds of walking. Of the various calf muscle Sto₂ measurements obtained during the treadmill test, the exercise time to the minimum calf muscle Sto₂ value (log transformed) had the strongest univariate associations with peak walking time (r = 0.56; P < .001), claudication onset time (r = 0.49; P < .001), 6-minute walk distance (r = 0.31; P < .001), WIQ distance score (r = 0.33; P < .001), WIQ speed score (r = 0.39; P < .001), WIQ stair-climbing score (r = 0.37; P < .001), and Medical Outcomes Study 36-Item Short Form Health Survey physical function score (r = 0.32; P < .001). In adjusted multiple regression models, these associations persisted (P < .001) after adjustment for demographic measures, cardiovascular risk factors, comorbid conditions, and ABI.

CONCLUSIONS

More rapid decline in oxygen saturation of the calf musculature during walking, indicative of impaired microcirculation, is predictive of impaired ambulatory function and HRQoL in patients with symptomatic PAD. Of particular importance, these associations are independent of ABI and other common health burdens, highlighting the clinical relevance that the microcirculation has on ambulatory function and HRQoL in patients with symptomatic PAD.

Pathophysiology of chronic peripheral ischemia: new perspectives

Peripheral arterial disease (PAD) affects individuals particularly over 65 years old in the more advanced countries. Hemodynamic, inflammatory, and oxidative mechanisms interact in the pathophysiological scenario of this chronic arterial disease. We discuss the hemodynamic, muscle tissue, and oxidative stress (OxS) conditions related to chronic ischemia of the peripheral arteries. This review summarizes the results of evaluating both metabolic and oxidative markers, and also therapy to counteract OxS. In conclusion, we believe different pathways should be highlighted to discover new drugs to treat patients suffering from PAD.

Effects of modified aerobic training on muscle metabolism in individuals with peripheral arterial disease: a randomized clinical trial

The primary objective of this study was to compare the effects on muscle metabolism of two types of aerobic training, with and without a load on the lower limbs, in adults with peripheral arterial disease (PAD). A simple blind randomized clinical trial was conducted using two groups: conventional aerobic (CG) and modified aerobic with a load on the lower limbs (MG). Both groups underwent training by walking three times a week over a 12-week period. The ratings of muscle metabolism were determined after a treadmill test with constant velocity and inclination concomitant with the use of near infrared spectroscopy (NIRS). Altogether 40 individuals with PAD (CG = 65.45 ± 10.60 and MG = 63.10 ± 10.54) were included in the study. After the intervention, in both groups, there was a reduction in the relative time to recovery (p = 0.002), an improvement in the re-oxygenation rate (p = 0.017), an increased time of resistance after reaching the lowest muscle oxygen saturation (StO₂) (p < 0.001), an increase in the distance walked (p < 0.001), and an improvement of the walking economy relative to StO₂ (p < 0.001). After 12 weeks of training, an improvement in the deoxygenation rate was observed in both groups (p = 0.002), but with a greater magnitude in the CG (p = 0.017). Only the CG presented an increase in time to reach the lowest StO₂ on the treadmill after the intervention (p = 0.010). The traditional aerobic training was superior to the modified training in relation to the improvement of muscle metabolism in patients with PAD.

A low-cost, wireless near-infrared spectroscopy device detects the presence of lower extremity atherosclerosis as measured by computed tomographic angiography and characterizes walking impairment in peripheral artery disease

BACKGROUND

Patients with peripheral artery disease (PAD) who experience intermittent claudication report a range of symptoms. Patients with symptoms other than classically described intermittent claudication may be at the highest risk for functional decline and mobility loss. Therefore, technologies allowing for characterization of PAD severity are desirable. Near-infrared spectroscopy (NIRS) allows for measurements of muscle heme oxygen saturation (StO₂) during exercise. We hypothesized lower extremities affected by PAD would exhibit distinct NIRS profiles as measured by a low-cost, wireless NIRS device and that NIRS during exercise predicts walking limitation.

METHODS

We recruited 40 patients with PAD and 10 control participants. All patients with PAD completed a computed tomographic angiography, 6-minute walk test, and a standardized treadmill test. Controls completed a 540-second treadmill test for comparison. StO₂ measurements were continuously taken from the gastrocnemius during exercise. Variables were analyzed by Fischer's exact, χ², Wilcoxon rank-sum, and Kruskal-Wallis tests as appropriate. Correlations were assessed by partial Spearman correlation coefficients adjusted for occlusive disease pattern.

RESULTS

Patients with PAD experienced claudication onset at a median of 108 seconds with a median peak walking time of 288 seconds. The baseline StO₂ was similar between PAD and control. The StO₂ of PAD and control participants dropped below baseline at a median of 1 and 104 seconds of exercise, respectively (P < .0001). Patients with PAD reached minimum StO₂ earlier than control participants (119 seconds vs 522 seconds, respectively; P < .001) and experienced a greater change in StO₂ at 1 minute of exercise (-73.2% vs 8.3%; P < .0001) and a greater decrease at minimum exercise StO₂ (-83.4% vs -16.1%; P < .0001). For patients with PAD, peak walking time, and 6-minute walking distance correlated with percent change in StO₂ at 1 minute of exercise (r = -0.76 and -0.67, respectively; P < .001) and time to minimum StO₂ (r = 0.79 and 0.70, respectively; P < .0001).

CONCLUSIONS

In this initial evaluation of a novel, low-cost NIRS device, lower extremities affected by PAD exhibited characteristic changes in calf muscle StO₂, which differentiated them from healthy controls and were strongly correlated with walking impairment. These findings confirm and expand on previous work demonstrating the potential clinical value of NIRS devices and the need for further research investigating the ability of low-cost NIRS technology to evaluate, diagnose, and monitor treatment response in PAD.

Diagnostic methods for measurement of peripheral blood flow during exercise in patients with type 2 diabetes and peripheral artery disease: a systematic review

INTRODUCTION

Measurement of systolic ankle and to some extent toe pressure in patients suffering from combined type 2 diabetes mellitus (T2DM) and peripheral arterial disease (PAD) face several obstacles due to complex changes in the vascular bed. The aim of this review was to address the current literature on blood flow during exercise in patients with PAD and T2DM and assess the feasibility of these methods to diagnose and grade arterial insufficiency.

EVIDENCE ACQUISITION

A systematic review of the PubMed and EMBASE databases, supplemented by hand searching was performed according to PRISMA guidelines. Clinical studies evaluating methods to investigate peripheral blood flow in patients with PAD and T2DM during exercise were included.

EVIDENCE SYNTHESIS

In total nine eligible studies consisting of 1105 non-diabetic PAD patients, 336 diabetic PAD patients, 161 diabetic patients without PAD and 69 healthy controls were included in the review. Near-infrared spectroscopy (NIRS) was described in three studies, transcutaneous oxygen pressure measurement (TcpO2) in two and the following methods described in single studies: thermodilution, contrast enhanced ultrasound (CEUS), scintigraphy and TcpO2 in combination with ultrasound. These studies shows that patients with PAD and T2DM compared with patients with only PAD suffers different atherosclerotic lesions characterised by increased arterial stiffness and microcirculation abnormalities, not well differentiated by pressure measurement alone. Investigating patients with PAD and T2DM during exercise reveals that NIRS, TcpO2, CEUS, and scintigraphy have distinct advantages over ankle and toe-pressure.

CONCLUSIONS

Using methods like NIRS, TcpO2, CEUS and scintigraphy, peripheral blood flow during exercise can be measured at a detailed level and potentially improve future severity grading in patients with combined T2DM and PAD.

Reduction of elevated lipids and low-density lipoprotein oxidation in serum of individuals with subclinical hypoxia and oxidative stress supplemented with lycosome formulation of docosahexaenoic acid

Thirty two individuals aged 40-65 years old with a moderate hyperlipidemia (serum triglycerides > 150 mg/dl and LDL from 130 to 160 mg/dl) were supplemented once daily for 30 days with a 250 mg conventional formulation of docosahexaenoic acid (DHA) without lycopene (CF-DHA) or 250 mg of lycosome-formulated DHA containing 7 mg of lycopene (LF-DHA). It was shown that ingestion of CF-DHA led to a transient increase in serum DHA level after 2 weeks of the trial, whereas LF-DHA did not cause significant changes in serum DHA. However, there was a noticeable increase in serum eicosapentaenoic acid levels exceeding the pretreatment value by 42.8% and 39.1% after the 2nd and 4th weeks of LF-DHA ingestion. Patients supplemented with LF-DHA showed a significant (19.5 mg/dl, p < 0.05) decline in LDL, which was accompanied by a corresponding decrease in total serum cholesterol and a much stronger reduction in serum triglyceride levels (reduction of medians by 27.5 mg/dl). No changes in HDL were observed. LF-DHA caused a significant decline in the serum level of malonic dialdehyde (MDA), whereas the components of LF-DHA, lycopene and DHA, ingested as two separate formulations had a less significant effect on serum MDA. Moreover, LF-DHA increased both the plasma oxygen transport and tissue oxygen saturation by the end of the observational period, while lycopene or DHA taken alone, or both of them co-ingested separately had none or a much less effect on the oxygen turnover parameters.

A comparison of different modes of pneumatic compression on muscle tissue oxygenation: An intraparticipant, randomised, controlled volunteer study

Intermittent pneumatic compression (IPC) to the lower limbs is widely used as a mechanical means to prevent deep vein thrombosis in hospitalised patients. Due to a theoretical concern about impairing blood flow, thromboembolic-deterrent stockings and IPC are considered contraindicated for patients with peripheral vascular diseases by some clinicians. This study assessed whether IPC would alter peripheral limb muscle tissue oxygenation (StO2), and whether such changes were different during 10 minutes of sequential and single-compartment compressions. Twenty volunteers were randomised to have their left or right arm treated with a sequential or single-compartment IPC for 10 minutes, using the contralateral arm without compression as an intraparticipant control. After a five-minute wash-out period, the procedure was repeated on the same arm using the alternative mode of IPC. Both hands’ thenar muscles StO2 was monitored every two minutes for 10 minutes using the same near-infrared spectroscopy StO2 monitor. Both sequential (3.5%, 95% confidence intervals (CI) 2.7–4.2; p < 0.001) and single-compartment IPC (1.6%, 95% CI 0.4–2.8; p = 0.039) significantly increased muscle StO2 within 10 minutes compared to no compression; and the increments were higher during sequential compressions compared to during single-compartment compressions (2.1%, 95% CI 0.7–3.5; p = 0.023). This mechanistic study showed that both modes of IPC increased upper limb muscle StO2 compared to no compression, but the StO2 increments were higher with the multiple-chamber sequential compressions mode. Contrary to the theoretical concern that IPC may impair peripheral limb tissue oxygenation, our results showed that IPC actually increases oxygenation of the peripheral limb muscles, especially during the sequential compressions mode.

Near-instant noninvasive optical imaging of tissue perfusion for vascular assessment

BACKGROUND

Noninvasive vascular tests are critical for identifying patients who may benefit from surgical revascularization, but current tests have significant limitations in people with diabetes. This study aimed to evaluate the ability of spatial frequency domain imaging (SFDI), an optical imaging method capable of measuring tissue oxygen saturation (StO₂) and tissue hemoglobin, to assess lower extremity blood supply.

METHODS

Ankle-brachial index, toe-brachial index, pedal Doppler waveforms, and SFDI images were prospectively evaluated in 47 consecutive patients with and without diabetes in whom there was concern for peripheral artery disease (PAD). SFDI is a noncontact optical imaging technology that uses structured illumination to quantify subsurface (2-3 mm in depth) StO₂ and tissue hemoglobin in the dermal microcirculation (HbT₁) and macrocirculation (HbT₂) over a large field of view (15 × 20 cm) within 10 seconds.

RESULTS

This demonstrates the ability of SFDI to capture reliable clinical measurements of perfusion in plantar aspects of the feet. SFDI StO₂ values differentiate nondiabetic patients with and without arterial disease, defined as ankle-brachial index <0.9 (P = .06), but are limited in those with diabetes (P = .43). An elevated StO₂ and reduced HbT₁ are observed in people with diabetes compared with nondiabetic patients (P < .05). An SFDI-derived HbT₂/HbT₁ index differentiates diabetics with PAD vs no PAD (P < .01) using toe-brachial index <0.7 as a cutoff for PAD in diabetes.

CONCLUSIONS

SFDI is a feasible, rapid, and easy to use widefield measurement of perfusion in a clinical setting. This first-of-use study suggests that the technology has potential to evaluate lower extremity perfusion in people with and without diabetes. Further studies with increased numbers of patients and end points including wound healing will need to be designed to fully evaluate the applicability of this new technology.

Oxygen availability and skeletal muscle oxidative capacity in patients with peripheral artery disease: implications from in vivo and in vitro assessments

Evidence suggests that the peak skeletal muscle mitochondrial ATP synthesis rate ( V_max) in patients with peripheral artery disease (PAD) may be attenuated due to disease-related impairments in O₂ supply. However, in vitro assessments suggest intrinsic deficits in mitochondrial respiration despite ample O₂ availability. To address this conundrum, Doppler ultrasound, near-infrared spectroscopy, phosphorus magnetic resonance spectroscopy, and high-resolution respirometry were combined to assess convective O₂ delivery, tissue oxygenation, V_max, and skeletal muscle mitochondrial capacity (complex I + II, state 3 respiration), respectively, in the gastrocnemius muscle of 10 patients with early stage PAD and 11 physical activity-matched healthy control (HC) subjects. All participants were studied in free-flow control conditions (FF) and with reactive hyperemia (RH) induced by a period of brief ischemia during the last 30 s of submaximal plantar flexion exercise. Patients with PAD repeated the FF and RH trials under hyperoxic conditions (FF + 100% O₂ and RH + 100% O₂). Compared with HC subjects, patients with PAD exhibited attenuated O₂ delivery at the same absolute work rate and attenuated tissue reoxygenation and V_max after relative intensity-matched exercise. Compared with the FF condition, only RH + 100% O₂ significantly increased convective O₂ delivery (~44%), tissue reoxygenation (~54%), and V_max (~60%) in patients with PAD ( P < 0.05), such that V_max was now not different from HC subjects. Furthermore, there was no evidence of an intrinsic mitochondrial deficit in PAD, as assessed in vitro with adequate O₂. Thus, in combination, this comprehensive in vivo and in vitro investigation implicates O₂ supply as the predominant factor limiting mitochondrial oxidative capacity in early stage PAD. NEW & NOTEWORTHY Currently, there is little accord as to the role of O₂ availability and mitochondrial function in the skeletal muscle dysfunction associated with peripheral artery disease. This is the first study to comprehensively use both in vivo and in vitro approaches to document that the skeletal muscle dysfunction associated with early stage peripheral artery disease is predominantly a consequence of limited O₂ supply and not the impact of an intrinsic mitochondrial defect in this pathology.

Calf Muscle Oxygen Saturation during 6-Minute Walk Test and Its Relationship with Walking Impairment in Symptomatic Peripheral Artery Disease

BACKGROUND

Impaired microcirculation is associated with poor walking capacity in symptomatic peripheral artery disease (PAD) patients during treadmill test; however, this test does not simulate the efforts of daily walking of these patients. Thus, the aim of the study was to describe the microcirculation responses during a 6-minute walk test (6MWT) and to analyze the relationship between microcirculation indicators and walking impairment in symptomatic PAD patients.

METHODS

Thirty-four patients were included (mean age = 67.6 ± 11.2 years). Their clinical characteristics were collected, and they performed a 6MWT, in which the initial claudication distance (ICD) and total walking distance (TWD) were recorded. During and after the 6MWT, calf muscle oxygen saturation (StO₂) parameters were monitored continuously to measure microcirculation behavior. The association between calf muscle StO₂ parameters and walking impairment were analyzed by Pearson or Spearman correlations.

RESULTS

Walking impairment was not associated with any StO₂ parameters during exercise. In contrast, after 6MWT, recovery time of StO₂ (r = -0.472, P = 0.008) and recovery time to maximal StO₂ (r = -0.402, P = 0.019) were negatively correlated with ICD. Furthermore, the distance walked under claudication symptoms (ΔTWD-ICD) was positively correlated with recovery time to maximal StO₂ (r = 0.347, P = 0.048).

CONCLUSIONS

In symptomatic PAD patients, shorter ICD values during a 6MWT are associated with a delayed recovery in calf muscle StO₂ after exercise. Calf muscle StO₂ parameters decrease subtly during 6MWT, suggesting that the degree of ischemia in the calf muscle during ground walking, simulating efforts of the daily walking, is relatively low.

Pharmacokinetics and Oxidation Parameters in Volunteers Supplemented with Microencapsulated Docosahexaenoic Acid

Context:

Docosahexaenoic acid (DHA) is an omega-3 fatty acid essential for cardiovascular health, brain development, and reproductive function. Due to hydrophobicity and low DHA bioavailability, new microencapsulated DHA formulations are under development.

Aim:

This study aims to evaluate DHA pharmacokinetics (PKs) and biological oxidation parameters in volunteers ingesting a newly developed lutein-containing lycosomal formulation of DHA (LF-DHA).

Materials and Methods:

A total of 32 healthy volunteers (40–65 years old) with signs of oxidative stress (OS) and subclinical hypoxia were orally supplemented for a month with 250 mg of regular DHA (1^st group) or a combination of lutein (7.0 mg) and zeaxanthin (1.4 mg) (2^nd group). The third group received regular DHA (250 mg) co-ingested with lutein/zeaxanthin (7.0/1.4 mg), whereas the 4^th group was given LF-DHA containing lutein/zeaxanthin (7.0/1.4 mg). PK, OS, and oxygenation parameters were analyzed.

Results:

LF-DHA improved the PKs of DHA enhancing its serum concentrations time dependently by 34.6% and 94.1% after 2^nd and 4^th weeks, respectively. DHA and lutein ingested either alone or simultaneously as two separate formulations reduced the levels of OS markers. However, LF-DHA inhibited the malonicdialdehyde (MDA) and oxidized low-density lipoprotein values were better than other formulations. LF-DHA also enhanced the plasma oxygen and tissue oxygen saturation. This effect was significantly higher than in other groups.

Conclusion:

LF-DHA eliminates the need in high-dose DHA supplementation protocols and confers a higher DHA bioavailability, thereby improving the parameters of biological oxidation and tissue respiration in affected individuals.

Effects of exercise training on calf muscle oxygen extraction and blood flow in patients with peripheral artery disease

We employed near-infrared optical techniques, diffuse correlation spectroscopy (DCS), and frequency-domain near-infrared spectroscopy (FD-NIRS) to test the hypothesis that supervised exercise training increases skeletal muscle microvascular blood flow and oxygen extraction in patients with peripheral artery disease (PAD) who experience claudication. PAD patients ( n = 64) were randomly assigned to exercise and control groups. Patients in the exercise group received 3 mo of supervised exercise training. Calf muscle blood flow and oxygen extraction were optically monitored before, during, and after performance of a graded treadmill protocol at baseline and at 3 mo in both groups. Additionally, measurements of the ankle-brachial index (ABI) and peak walking time (PWT) to maximal claudication were made during each patient visit. Supervised exercise training was found to increase the maximal calf muscle blood flow and oxygen extraction levels during treadmill exercise by 29% (13%, 50%) and 8% (1%, 12%), respectively [ P < 0.001; median (25th percentile, 75th percentile)]. These improvements across the exercise group population were significantly higher than corresponding changes in the control group ( P < 0.004). Exercise training also increased PWT by 49% (18%, 101%) ( P = 0.01). However, within statistical error, the ABI, resting calf muscle blood flow and oxygen extraction, and the recovery half-time for hemoglobin\myoglobin desaturation following cessation of maximal exercise were not altered by exercise training. The concurrent monitoring of both blood flow and oxygen extraction with the hybrid DCS/FD-NIRS instrument revealed enhanced muscle oxidative metabolism during physical activity from exercise training, which could be an underlying mechanism for the observed improvement in PWT. NEW & NOTEWORTHY We report on noninvasive optical measurements of skeletal muscle blood flow and oxygen extraction dynamics before/during/after treadmill exercise in peripheral artery disease patients who experience claudication. The measurements tracked the effects of a 3-mo supervised exercise training protocol and revealed that supervised exercise training improved patient ability to increase microvascular calf muscle blood flow and oxygen extraction during physical activity.

Oxygen consumption of gastrocnemius medialis muscle during submaximal voluntary isometric contractions with and without preceding stretch

After an active muscle stretch, maintaining a certain amount of force in the following isometric phase is accompanied by less muscle activation compared to an isometric contraction without preceding active stretch at the corresponding muscle length. This reduced muscle activation might be related to reduced metabolic costs, such as the oxidative metabolism. Hence, the aim of this study was to clarify if mechanisms associated with stretch-induced activation reduction (AR) also influence oxygen consumption of voluntary activated human muscles after active stretch. Plantarflexion torque of 20 subjects was measured during 1) purely isometric and 2) active stretch contractions (26°, 60°/s), at a submaximal torque level of 30% MVC. Oxygen consumption (m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{\rm{V}}$$\end{document}V·O₂) of gastrocnemius medialis (GM) was estimated by near-infrared spectroscopy while applying arterial occlusion. Since the overall group did not show AR at GM after active stretch (p > 0.19), a subgroup was defined (n = 10) showing AR of 13.0 ± 10.3% (p = 0.00). However, for both purely isometric and active contractions m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{\rm{V}}$$\end{document}V·O₂ was the same (p = 0.32). Therefore, AR triggered by active stretch did not affect m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{\rm{V}}$$\end{document}V·O₂ of active human muscle.

Exercise training in older adults, what effects on muscle oxygenation? A systematic review

AIM

To determine the effects of different modality of exercise training programs on muscle oxygenation in older adults.

METHODS

Relevant articles were searched in PubMed, Web of Science, Science Direct and Scopus, using the keywords: "Aged" AND "Muscle oxygenation" AND (Exercise OR "Exercise therapy" OR "Exercise Movement Techniques" OR Hydrotherapy), without limitation concerning the publication date. To be included in the full analysis, the study had to be a randomized controlled trial in which older adults participants (mean age: 65 years at least) were submitted to an exercise-training program and muscle oxygenation assessment.

RESULTS

The searches resulted in 1238 articles from which 7 met all the inclusion criteria. The trials involved 370 older adults (68.7±1.7years), healthy and with peripheral arterial disease. Studies included resistance and endurance exercises as well as walking sessions. Training sessions were 2-6 time per week, lasted 3-24 months and with different training intensity throughout studies. After a long-term resistance training, healthy older adults showed enhanced muscle oxygen extraction capacity, regulation of vessels and vascular endothelium function; endurance training is reported to improve microvascular blood flow and matching of oxygen delivery to oxygen utilization, muscle oxidative capacity and muscle saturation, and walking sessions results in better muscle oxygen availability and muscle oxygen extraction capacity in older adults with peripheral arterial disease.

CONCLUSIONS

This review supports the fact that depending on the clinical status of the participants and the modality, exercise training improves different aspects of the muscle oxygenation in older adults.

Mitochondrial Bioenergetics in the Metabolic Myopathy Accompanying Peripheral Artery Disease

Peripheral artery disease (PAD) is a serious but relatively underdiagnosed and undertreated clinical condition associated with a marked reduction in functional capacity and a heightened risk of morbidity and mortality. The pathophysiology of lower extremity PAD is complex, and extends beyond the atherosclerotic arterial occlusion and subsequent mismatch between oxygen demand and delivery to skeletal muscle mitochondria. In this review, we evaluate and summarize the available evidence implicating mitochondria in the metabolic myopathy that accompanies PAD. Following a short discussion of the available in vivo and in vitro methodologies to quantitate indices of muscle mitochondrial function, we review the current evidence implicating skeletal muscle mitochondrial dysfunction in the pathophysiology of PAD myopathy, while attempting to highlight questions that remain unanswered. Given the rising prevalence of PAD, the detriment in quality of life for patients, and the associated significant healthcare resource utilization, new alternate therapies that ameliorate lower limb symptoms and the functional impairment associated with PAD are needed. A clear understanding of the role of mitochondria in the pathophysiology of PAD may contribute to the development of novel therapeutic interventions.

Quantifying the effect of adipose tissue in muscle oximetry by near infrared spectroscopy

Change of muscle tissue oxygen saturation (StO2), due to exercise, measured by near infrared spectroscopy (NIRS) is known to be lower for subjects with higher adipose tissue thickness. This is most likely not physiological but caused by the superficial fat and adipose tissue. In this paper we assessed, in vitro, the influence of adipose tissue thickness on muscle StO2, measured by NIRS oximeters. We measured StO2 of a liquid phantom by 3 continuous wave (CW) oximeters (Sensmart Model X-100 Universal Oximetry System, INVOS 5100C, and OxyPrem v1.3), as well as a frequency-domain oximeter, OxiplexTS, through superficial layers with 4 different thicknesses. Later, we employed the results to calibrate OxyPrem v1.3 for adipose tissue thickness in-vivo.

Pain description in patients with isolated proximal (without distal) exercise-related lower limb arterial ischemia

Among the last 250 claudicants referred to the laboratory for transcutaneous oxygen pressure recording at exercise, we analyzed the symptoms reported by the 36 patients who showed isolated proximal (without distal) ischemia. Among the symptomatic proximal sites cited by these patients, the hip and thigh represent 60%, whereas the buttock is cited in fewer than 25% of cases. Buttock symptoms are reported in only 31% of symptomatic patients. ‘Buttock’ claudication is probably not the dominant symptom in isolated proximal vascular ischemia. Assessing proximal lower limb ischemia through the sole detection of ‘buttock pain’ could contribute to the underestimation of proximal vascular ischemia.

Cutaneous Imaging Technologies in Acute Burn and Chronic Wound Care

BACKGROUND

Wound assessment relies on visual evaluation by physicians. Such assessment is largely subjective and presents the opportunity to explore the use of emergent technologies.

METHODS

Emergent and powerful noninvasive imaging technologies applicable to assess burn and chronic wounds are reviewed.

RESULTS

The need to estimate wound depth is critical in both chronic wound and burn injury settings. Harmonic ultrasound technology is powerful to study wound depth. It addresses the limitations of optical imaging with limited depth of penetration. What if a wound appears epithelialized by visual inspection, which shows no discharge yet is covered by repaired skin that lacks barrier function? In this case although the wound is closed as defined by current standards, it remains functionally open, presenting the risk of infection and other postclosure complications. Thus, assessment of skin barrier function is valuable in the context of assessing wound closure. Options for the study of tissue vascularization are many. If noncontact and noninvasive criteria are of importance, laser speckle imaging is powerful. Fluorescence imaging is standard in several clinical settings and is likely to serve the wound clinics well as long as indocyanine green injection is not of concern. A major advantage of harmonic ultrasound imaging of wound depth is that the same system is capable of providing information on blood flow dynamics in arterial perforators.

CONCLUSION

With many productive imaging platforms to choose from, wound care is about to be transformed by technology that would help assess wound severity.

The effect of current cigarette smoking on calf muscle hemoglobin oxygen saturation in patients with intermittent claudication

The purpose of this study was to compare calf muscle hemoglobin oxygen saturation response during exercise between smokers and non-smokers with peripheral arterial disease. Patients limited by intermittent claudication who were smokers (n = 12) were compared with those who had not smoked (n = 28) for at least 1 year prior to investigation. Ankle/brachial index (ABI) measurements were obtained with Doppler ultrasound, and maximal calf blood flow was measured by venous occlusion plethysmography. Hemoglobin oxygen saturation (StO2) of the calf muscle, initial claudication distance (ICD), and absolute claudication distance (ACD) were obtained during a graded treadmill test. Smokers refrained from smoking on the morning of the test. Smokers had similar ABI values compared with non-smokers (0.70 ± 0.26 vs 0.73 ± 0.23 [mean ± SD]; p = 0.808), whereas the smokers had lower values for maximal calf blood flow (8.71 ± 5.76 %/min vs 11.48 ± 4.46 %/min; p = 0.038), ICD (122 ± 123 m vs 243 ± 177 m; p = 0.023), and ACD (284 ± 170 m vs 452 ± 263 m; p = 0.023). Additionally, smokers had lower calf muscle StO2 values at the end of 1 minute (16 ± 15% vs 37 ± 19%; p = 0.002) and 2 minutes of exercise (16 ± 16% vs 35 ± 25%; p = 0.008), and at the occurrence of ICD (17 ± 17% vs 32 ± 23%; p = 0.033) and ACD (16 ± 16% vs 32 ± 24%; p = 0.024). After adjusting for blood flow, calf muscle StO2 values remained lower in the smokers (p < 0.05). Finally, calf muscle StO2 at the end of the first minute of exercise was related to ICD (r = 0.611, p < 0.001) and ACD (r = 0.443, p < 0.01). In conclusion, smokers limited by intermittent claudication have lower calf muscle StO2 during exercise than nonsmokers, and lower StO2 during exercise is associated with shorter ICD and ACD.

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.

Internal Iliac Artery Stenosis: Diagnosis and How to Manage it in 2015

Lower extremity arterial disease (LEAD) is a highly prevalent disease affecting 202 million people worldwide. Internal iliac artery stenosis (IIAS) is one of the localization of LEAD. This diagnosis is often neglected when a patient has a proximal walking pain since most physicians evoke a pseudoclaudication. Surprisingly, IIAS management is reported neither in the Trans-Atlantic Inter-Society Consensus II nor in the report of the American College Foundation/American Heart Association guidelines. The aims of this review are to present the current knowledge about the disease, how should it be managed in 2015 and what are the future research trends.

The First-in-Man "Si Se Puede" Study for the use of micro-oxygen sensors (MOXYs) to determine dynamic relative oxygen indices in the feet of patients with limb-threatening ischemia during endovascular therapy

OBJECTIVE

Patients with limb-threatening ischemia exhibit uneven patterns of perfusion in the foot, which makes it challenging to determine adequate topographic perfusion by angiography alone. This study assessed the feasibility of reporting dynamic relative oxygen indices and tissue oxygen concentration from multiple locations on the foot during endovascular therapy using a novel micro-oxygen sensor (MOXY; PROFUSA, Inc, South San Francisco, Calif) approach.

METHODS

A prospective, 28-day, single-arm, observational study was performed in 10 patients who underwent endovascular therapy for limb-threatening ischemia. At least 24 hours before therapy, four microsensors were injected in each patient (one in the arm, three in the treated foot). The optical signal from the microsensors corresponded to tissue oxygen concentration. A custom detector on the surface of the skin was used to continuously and noninvasively measure the signals from the microsensors. The ability to locate and read the signal from each injected microsensor was characterized. Oxygen data from the microsensors were collected throughout the revascularization procedure. The timing of therapy deployment was recorded during the procedure to assess its relationship with the microsensor oxygen data. Oxygen data collection and clinical evaluation were performed immediately postoperatively as well as postoperatively on days 7, 14, 21, and 28.

RESULTS

The study enrolled 10 patients (50% male) with ischemia (30% Rutherford class 4, 70% Rutherford class 5). Patients were a mean age of 70.7 years (range, 46-90 years), and all were Hispanic of varying origin. Microsensors were successfully read 206 of 212 times (97.2%) in all patients during the course of the study. Microsensors were compatible with intraoperative use in the interventional suite and postoperatively in an office setting. In nine of 10 revascularization procedures, at least one of the three MOXYs showed an immediate change in the dynamic relative oxygen index, correlating to deployed therapy. Moreover, there was a statistically significant increase in the concentration of oxygen in the foot in preoperative levels compared with postoperative levels. No adverse events occurred related to the microsensor materials.

CONCLUSIONS

This MOXY approach appears to be safe when implanted in patients with limb-threatening ischemia undergoing endovascular recanalization and is effective in reporting local tissue oxygen concentrations over a course of 28 days. Further testing is needed to determine its potential effect on clinical decision making, both acutely on-table and chronically as a surveillance modality, which ultimately can lead to improved healing and limb salvage.

Low tissue oxygen saturation is associated with requirements for transfusion in the rural trauma population

BACKGROUND

Tissue O2 saturation (StO2) is a measure of tissue perfusion and should decrease during active hemorrhage. An initial StO2 value upon trauma center arrival measured concurrently with or prior to vitals, may predict hemorrhagic shock, requiring early blood product transfusion. Our aim was to identify the early StO2 threshold associated with a greater volume of packed red blood cell (PRBC) transfusion 24 h after injury.

METHODS

All highest tier triage trauma patients from January 2011 to July 2012 were included in this study. The initial StO2 value upon arrival was used for comparison.

RESULTS

A total of 632 patients were considered, 74% of them male with a mean age of 46 years. Initial StO2 values were available for 325 patients. An StO2 value of 65% was determined as the cutoff due to the marked increase in PRBC consumption in 24 h. There were 23 patients (7%) with an StO2 reading <65% compared to 302 patients with values ≥65%. Both groups had similar systolic blood pressure (118 vs. 126) and heart rate (99 vs. 95) in the trauma bay. In addition, there was no difference in the initial hemoglobin, pH, or base deficit. An early StO2 value <65% also led to a greater number of PRBC transfused in 24 h (6.4 vs. 1.7). Regression analysis demonstrated that an StO2 <65% was the only variable associated with a higher PRBC transfusion volume in 24 h (p = 0.01).

CONCLUSIONS

An StO2 value <65% correlates with greater requirement for PRBC transfusion 24 h after injury. This suggests that StO2 can be used as an early marker of hemorrhage which may be superior to traditional vital signs in the trauma population.

Global positioning system use in the community to evaluate improvements in walking after revascularization: a prospective multicenter study with 6-month follow-up in patients with peripheral arterial disease

Revascularization aims at improving walking ability in patients with arterial claudication. The highest measured distance between 2 stops (highest-MDCW), the average walking speed (average-WSCW), and the average stop duration (average-DSCW) can be measured by global positioning system, but their evolution after revascularization is unknown.We included 251 peripheral artery diseased patients with self-reported limiting claudication. The patients performed a 1-hour stroll, recorded by a global positioning system receiver. Patients (n = 172) with confirmed limitation (highest-MDCW <2000m) at inclusion were reevaluated after 6 months. Patients revascularized during the follow-up period were compared with reference patients (ie, with unchanged lifestyle medical or surgical status). Other patients (lost to follow-up or treatment change) were excluded (n = 89).We studied 44 revascularized and 39 reference patients. Changes in highest-MDCW (+442 vs. +13 m) and average-WSCW (+0.3 vs. -0.2 km h) were greater in revascularized than in reference patients (both P < 0.01). In contrast, no significant difference in average-DSCW changes was found between the groups. Among the revascularized patients, 13 (29.5%) had a change in average-WSCW, but not in highest-MDCW, greater than the mean + 1 standard deviation of the change observed for reference patients.Revascularization may improve highest-MDCW and/or average-WSCW. This first report of changes in community walking ability in revascularized patients suggests that, beyond measuring walking distances, average-WSCW measurement is essential to monitor these changes. Applicability to other surgical populations remains to be evaluated.

REGISTRATION

http://www.clinicaltrials.gov/ct2/show/NCT01141361.

Empirical mode decomposition analysis of near-infrared spectroscopy muscular signals to assess the effect of physical activity in type 2 diabetic patients

Type 2 diabetes is a metabolic disorder that may cause major problems to several physiological systems. Exercise has proven to be very effective in the prevention, management and improvement of this pathology in patients. Muscle metabolism is often studied with near-infrared spectroscopy (NIRS), a noninvasive technique that can measure changes in the concentration of oxygenated (O2Hb) and reduced hemoglobin (HHb) of tissues. These NIRS signals are highly non-stationary, non-Gaussian and nonlinear in nature. The empirical mode decomposition (EMD) is used as a nonlinear adaptive model to extract information present in the NIRS signals. NIRS signals acquired from the tibialis anterior muscle of controls and type 2 diabetic patients are processed by EMD to yield three intrinsic mode functions (IMF). The sample entropy (SE), fractal dimension (FD), and Hurst exponent (HE) are computed from these IMFs. Subjects are monitored at the beginning of the study and after one year of a physical training programme. Following the exercise programme, we observed an increase in the SE and FD and a decrease in the HE in all diabetic subjects. Our results show the influence of physical exercise program in improving muscle performance and muscle drive by the central nervous system in the patients. A multivariate analysis of variance performed at the end of the training programme also indicated that the NIRS metabolic patterns of controls and diabetic subjects are more similar than at the beginning of the study. Hence, the proposed EMD technique applied to NIRS signals may be very useful to gain a non-invasive understanding of the neuromuscular and vascular impairment in diabetic subjects.

Sildenafil improves skeletal muscle oxygenation during exercise in men with intermittent claudication

Endothelial dysfunction caused by defective nitric oxide (NO) signaling plays a pivotal role in the pathogenesis of intermittent claudication (IC). In the present study, we evaluated the acute effects of sildenafil, a phosphodiesterase type 5 inhibitor that acts by prolonging NO-mediated cGMP signaling in vascular smooth muscle, on blood pressure (BP), skeletal muscle oxygenation, and walking tolerance in patients with IC. A randomized, double-blind, crossover study was conducted in which 12 men with stable IC received two consecutive doses of 50 mg of sildenafil or matching placebo and underwent a symptom-limited exercise test on the treadmill. Changes in gastrocnemius deoxy-hemoglobin by near-infrared spectroscopy estimated peripheral muscle O2delivery-to-utilization matching. Systolic BP was significantly lower during the sildenafil trial relative to placebo during supine rest (∼15 mmHg), submaximal exercise (∼14 mmHg), and throughout recovery (∼18 mmHg) ( P < 0.05). Diastolic BP was also lower after sildenafil during upright rest (∼6 mmHg) and during recovery from exercise (∼7 mmHg) ( P < 0.05). Gastrocnemius deoxygenation was consistently reduced during submaximal exercise (∼41%) and at peak exercise (∼34%) following sildenafil compared with placebo ( P < 0.05). However, pain-free walking time (placebo: 335 ± 42 s vs. sildenafil: 294 ± 35 s) and maximal walking time (placebo: 701 ± 58 s vs. sildenafil: 716 ± 62 s) did not differ between trials. Acute administration of sildenafil lowers BP and improves skeletal muscle oxygenation during exercise but does not enhance walking tolerance in patients with IC. Whether the beneficial effects of sildenafil on muscle oxygenation can be sustained over time and translated into positive clinical outcomes deserve further consideration in this patient population.

Bedside assessment of tissue oxygen saturation monitoring in critically ill adults: an integrative review of the literature

Objective. Tissue oxygen saturation (StO2) monitoring is a noninvasive technology with the purpose of alerting the clinician of peripheral hypoperfusion and the onset of tissue hypoxia. This integrative review examines the rigor and quality of studies focusing on StO2 monitoring in adult critically ill patients. Background. Clinicians must rapidly assess adverse changes in tissue perfusion while minimizing potential complications associated with invasive monitoring. The noninvasive measurement of tissue oxygen saturation is based on near-infrared spectroscopy (NIRS), an optical method of illuminating chemical compounds which absorb, reflect, and scatter light directed at that compound. Methods. An integrative review was conducted to develop a context of greater understanding about complex topics. An Integrative review draws on multiple experimental and nonexperimental research methodologies. Results. Fourteen studies were graded at the C category. None reported the use of probability sampling or demonstrated a cause-and-effect relationship between StO2 values and patient outcomes. Conclusions. Future research should be based on rigorous methods of sampling and design in order to enhance the internal and external validity of the findings.

Lumbar sympathicolysis in patients with severe peripheral artery disease: hemodynamics of the lower limbs determined by near-infrared spectroscopy, color coded duplex sonography, and temperature measurement

The objective was to investigate the effects of CT-guided lumbar sympathicolysis on somatic regional oxygen saturation, arterial flow velocity, and skin temperature of the lower limbs in patients with advanced peripheral artery disease (PAD). CT-guided lumbar sympathicolysis was additionally performed after successful revascularization therapy in 61 patients with PAD in categories 5 and 6 according to Rutherford. Somatic regional oxygen saturation in the distal lower limbs was determined semiquantitatively with a near-infrared spectroscopy (NIRS) system. Before and after intervention, peak flow and end-diastolic flow velocity in the dorsalis pedis artery were determined by means of color-coded duplex sonography, and the skin temperature of the feet was measured with an infrared thermometer. After CT-guided lumbar sympathicolysis, somatic regional oxygen saturation, peak flow, end-diastolic flow velocity, and skin temperature in the lower limbs increased significantly.

Entropy analysis of muscular near-infrared spectroscopy (NIRS) signals during exercise programme of type 2 diabetic patients: quantitative assessment of muscle metabolic pattern

Diabetes mellitus (DM) is a metabolic disorder that is widely rampant throughout the world population these days. The uncontrolled DM may lead to complications of eye, heart, kidney and nerves. The most common type of diabetes is the type 2 diabetes or insulin-resistant DM. Near-infrared spectroscopy (NIRS) technology is widely used in non-invasive monitoring of physiological signals. Three types of NIRS signals are used in this work: (i) variation in the oxygenated haemoglobin (O2Hb) concentration, (ii) deoxygenated haemoglobin (HHb), and (iii) ratio of oxygenated over the sum of the oxygenated and deoxygenated haemoglobin which is defined as: tissue oxygenation index (TOI) to analyze the effect of exercise on diabetes subjects. The NIRS signal has the characteristics of non-linearity and non-stationarity. Hence, the very small changes in this time series can be efficiently extracted using higher order statistics (HOS) method. Hence, in this work, we have used sample and HOS entropies to analyze these NIRS signals. These computer aided techniques will assist the clinicians to diagnose and monitor the health accurately and easily without any inter or intra observer variability. Results showed that after a one-year of physical exercise programme, all diabetic subjects increased the sample entropy of the NIRS signals, thus revealing a better muscle performance and an improved recruitment by the central nervous system. Moreover, after one year of physical therapy, diabetic subjects showed a NIRS muscular metabolic pattern that was not distinguished from that of controls. We believe that sample and bispectral entropy analysis is need when the aim is to compare the inner structure of the NIRS signals during muscle contraction, particularly when dealing with neuromuscular impairments.

FEATURE SELECTION APPLIED TO THE TIME-FREQUENCY REPRESENTATION OF MUSCLE NEAR-INFRARED SPECTROSCOPY (NIRS) SIGNALS: CHARACTERIZATION OF DIABETIC OXYGENATION PATTERNS

Diabetic patients might present peripheral microcirculation impairment and might benefit from physical training. Thirty-nine diabetic patients underwent the monitoring of the tibialis anterior muscle oxygenation during a series of voluntary ankle flexo-extensions by near-infrared spectroscopy (NIRS). NIRS signals were acquired before and after training protocols. Sixteen control subjects were tested with the same protocol. Time-frequency distributions of the Cohen's class were used to process the NIRS signals relative to the concentration changes of oxygenated and reduced hemoglobin. A total of 24 variables were measured for each subject and the most discriminative were selected by using four feature selection algorithms: QuickReduct, Genetic Rough-Set Attribute Reduction, Ant Rough-Set Attribute Reduction, and traditional ANOVA. Artificial neural networks were used to validate the discriminative power of the selected features. Results showed that different algorithms extracted different sets of variables, but all the combinations were discriminative. The best classification accuracy was about 70%. The oxygenation variables were selected when comparing controls to diabetic patients or diabetic patients before and after training. This preliminary study showed the importance of feature selection techniques in NIRS assessment of diabetic peripheral vascular impairment.