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

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.

Impact of Peripheral Angioplasty on Wound Oxygenation and Healing in Patients with Chronic Limb-Threatening Ischemia Measured by Near-Infrared Spectroscopy

Managing chronic limb-threatening ischemia (CLTI) is challenging due to difficulties in assessing tissue oxygen saturation in ulcers. Near-infrared spectroscopy (NIRS) is a non-invasive method for measuring tissue oxygen saturation (StO2). This study evaluated the effects of endovascular treatment (EVT) on StO2 and wound healing in CLTI patients, comparing NIRS to standard ankle-brachial index (ABI) measurements. Using the Duesseldorf PTA Registry, 43 CLTI patients were analyzed: 27 underwent EVT, and 16 received conservative treatment. ABI assessed macrocirculation, while NIRS measured wound, wound area, and mean foot StO2 at baseline, post-EVT, and four-month follow-up. Wound severity was classified by wound area and wound, ischemia, and foot infection (WIfI) score. Wound StO2 increased significantly (median (interquartile range (IQR)), 38 (49.3) to 60 (34.5)%, p = 0.004), as did wound area StO2 (median (IQR), 70.9 (21.6) to 72.8 (18.3)%, p < 0.001), with no significant changes in the control group by four-month follow-up. Wound area decreased significantly after EVT (mean ± SD, 343.1 ± 267.8 to 178.1 ± 268.5 mm2, p = 0.01) but not in the control group. Changes in wound StO2, wound area StO2, and WIfI score correlated with wound area reduction, unlike ABI. This small exploratory study shows that NIRS-measured StO2 improvements after EVT correlate with reduced wound area and WIfI scores, highlighting NIRS as a potential enhancement for CLTI wound management in addition to ABI.

Duplex ultrasound and pedal acceleration time as tools to evaluate foot perfusion: a literature review

Currently, the standard non-invasive test for diagnosing Peripheral Arterial Disease is the Ankle-Brachial Index. However, this test becomes unfeasible in a certain population. New evidence proposes the pedal acceleration time, an ultrasound index, as an alternative test. An integrative bibliographic review was carried out between June 3, 2022 and January 8, 2023, to investigate this new index as a tool to assess foot perfusion. Papers published in English, Portuguese, or Spanish between 2012 and 2022 were searched on PubMed, Google Scholar, and Scielo, using the keywords "Peripheral Arterial Disease" AND "Acceleration Time" AND (Pedal OR Plantar). Research that didn't assess foot perfusion using the methods of interest or did not present human data and also case series or reports were excluded. Seven out of the sixty-six articles identified in the searches were selected for the review, all of which had notable methodological limitations. Pedal acceleration time seems to be able to diagnose and stratify and may reflect prognosis.

Near-infrared spectroscopy data for foot skin oxygen saturation in healthy subjects

Our objective was to evaluate normative data for near-infrared spectroscopy (NIRS) in 110 healthy volunteers by Fitzpatrick skin type (FST) and region of the foot. We obtained measurements of the dorsum and plantar foot using a commercially available device (SnapshotNIR, Kent Imaging, Calgary Canada). On the dorsum of the foot, people with FST6 had significantly lower oxygen saturation compared to FST1-5 (p < 0.001), lower oxyhaemoglobin compared to FST2-5 (p = 0.001), but there was no difference in deoxyhaemoglobin. No differences were found on the plantar foot. When comparing dorsal and plantar foot, there was higher oxyhaemoglobin (0.40 ± 0.09 vs. 0.51 ± 0.12, p < 0.001) and deoxyhaemoglobin (0.16 ± 0.05 vs. 0.21 ± 0.05, p < 0.001) on the plantar foot, but no differences in oxygen saturation (dorsal 70.7 ± 10.8, plantar 70.0 ± 9.5, p = 0.414). In 6.4% of feet, there were black areas, for which no NIRS measurements could be generated. All areas with no data were on the dorsal foot and only found in FST 5-6. People with FST6 had significantly larger areas with no data compared to FST 5 (22.2 cm2  ± 20.4 vs. 1.9 cm2  ± 0.90, p = 0.007). These findings should be considered when using NIRS technology. Skin pigmentation should be evaluated in future NIRS studies.

Oxygen Therapy to Enhance Wound Healing After Revascularization

Oxygen is one of the important factors for wound healing and infection control. The revascularization procedure is amended to correct the tissue hypoxia problem by increasing the blood flow to obtain an adequate amount of oxygen. Hypoxic wounds are still the issue in the cases of unsuccessful or incomplete revascularization. The issue needs to be clarified and confirmed by proper methods for management to achieve wound healing and prevent limb loss. Oxygen therapy may benefit in the case of remaining hypoxia or wound infection in postrevascularization.

[Evaluation of revascularization efficiency using near-infrared oximetry in patients with diabetic foot syndrome]

OBJECTIVE

To evaluate prognostic significance of tissue oximetry in healing of trophic defects in patients with diabetic foot syndrome (DFS) after endovascular revascularization.

MATERIAL AND METHODS

In 42 patients with DFS, tissue oximetry was performed in angiosome projection with the FORE-SIGHT MC-2000 (CASMED) device before and the next day after revascularization of lower limb arteries. The 1st group included 30 patients with wound healing throughout 3 months, the 2nd group included 12 patients with amputation or no healing of trophic defects.

RESULTS

Direct revascularization was more common in the 1st group (p=0.001). On the day after intervention, oxygen saturation (StO2) increased in all angiosomes in both groups (p<0.05). StO2 increment differed significantly between groups in all angiosomes except for point I (p<0.05). According to ROC analysis, StO2 increment by 4.5% in absolute values and 7.9% in percentage leads to trophic defect healing within 3 months (sensitivity and specificity were 76.7% and 66.7% for absolute values, 80% and 58.3% for percentage, respectively).

CONCLUSION

Evaluation of StO2 in target angiosome may be valuable to predict trophic defect healing after endovascular surgery.

Incoherent optical fluctuation flowmetry for detecting limbs with hemodynamically significant stenoses in patients with type 2 diabetes

INTRODUCTION

The development of new highly accurate, inexpensive and accessible methods for the detection of lower-extremity peripheral artery disease (LE-PAD) in diabetic patients is required. The aim of this study was to evaluate the accuracy of a new incoherent optical fluctuation flowmetry (IOFF) method in detecting legs with hemodynamically significant stenoses compared to ankle brachial index (ABI) and transcutaneous oximetry (TcPO2) in patients with diabetes mellitus (DM).

MATERIALS AND METHODS

Patients were recruited into 2 groups. Group 1 included patients with DM without LE-PAD and/or diabetic foot syndrome; Group 2 included patients with DM and LE-PAD. All patients underwent the following measurements: ultrasound (reference method), ABI, TcPO2, and the new IOFF method.

RESULTS

The new IOFF method showed a sensitivity of 79.5% and a specificity of 89.8% in detecting limbs with hemodynamically significant stenosis (AUC 0.890, CI 0.822-0.957). TcpO2 allows the diagnosis of LE-PAD with 69.2% sensitivity and 86.2% specificity (AUC 0.817, CI 0.723-0.911). Using a standard ABI cut-off of less than 0.9, the sensitivity and specificity for this parameter were 34.5% and 89.7%, respectively. Increasing the diagnostic cut-off of the ABI on the study group to 0.99 improved sensitivity to 84.6% and specificity to 78% (AUC,0.824 CI 0.732-0.915).

CONCLUSIONS

The new IOFF technique has demonstrated high sensitivity and specificity in the detection of LE-PAD in patients with DM. The high accuracy, rapid measurement, and potential availability suggest that the new IOFF method has a high potential for clinical application in the detection of PAD.

rSO2 Measurement Using NIRS for Lower-Limb Blood Flow Monitoring and Estimation of Safe Balloon Occlusion/Deflation Time in Patients with PAS Who Underwent PBOA during CS

We examined the utility of regional oxygen saturation (rSO2) measurement using near-infrared spectroscopy (NIRS) for monitoring lower-limb blood flow and estimate the safe balloon occlusion/deflation time in patients with PAS who underwent prophylactic balloon occlusion of the abdominal artery (PBOA) during cesarean section (CS). During CS, the NIRS probes were positioned on either of the anterior tibial muscles. rSO2 was measured continuously during balloon occlusion/deflation. A cycle consisted of inflating the aortic balloon for 30 min and deflating it for 5 min. The rSO2 before/during balloon occlusion and after 5 min of balloon deflation were evaluated. Sixty-two lower limbs (fifteen women and data from 31 sessions of balloon inflation/deflation) were evaluated. rSO2 during balloon occlusion was significantly lower than rSO2 before balloon occlusion (57.9% ± 9.6% vs. 80.3% ± 6.0%; p < 0.01). There were no significant differences between rSO2 before balloon occlusion and rSO2 after 5 min of balloon deflation (80.3% ± 6.0% vs. 78.7% ± 6.6%; p = 0.07). Postoperatively, the lower limbs showed no ischemic symptoms. NIRS can assess lower-limb rSO2 during PBOA for PAS in real time to determine ischemia severity, duration, and recovery capacity.

Chronic PCSK9 inhibitor therapy leads to sustained improvements in endothelial function, arterial stiffness, and microvascular function

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 inhibitors (PCSK9i) effectively decrease low-density lipoprotein cholesterol (LDL-C) and reduce cardiovascular events in patients at very high cardiovascular risk. Recent short-term studies suggest a partially LDL-C independent beneficial effect of PCSK9 inhibitor (PCSK9i) therapy on endothelial function and arterial stiffness, whereas it is unknown if this effect persists and what the effect is on microcirculation.

OBJECTIVE

To investigate the effects of PCSK9i therapy on vascular parameters beyond its lipid lowering effect.

METHODS

In this prospective trial, 32 patients at very high cardiovascular risk and indication for PCSK9i therapy were included. Measurements were performed at baseline and after 6 months of PCSK9i treatment. Endothelial function was assessed as flow-mediated dilation (FMD). Arterial stiffness was measured as pulse wave velocity (PWV) and aortic augmentation index (AIx). Peripheral tissue oxygenation (StO₂) as a marker of microvascular function was assessed at the distal extremities using near-infrared spectroscopy camera.

RESULTS

Six months of PCSK9i therapy decreased LDL-C levels from 141 ± 54 to 60 ± 30 mg/dl (-56 ± 21 %, p < 0.001), FMD significantly increased from 5.4 ± 1.7 % to 6.4 ± 1.9 % (+19 ± 10 %, p < 0.001), PWV decreased in male patients significantly from 8.9 ± 2.1 to 7.9 ± 1.5 m/s (-12 ± 9 %, p = 0.025). AIx decreased from 27.1 ± 10.4 % to 23.0 ± 9.7 % (-16 ± 14 %, p < 0.001), StO₂ significantly increased from 67 ± 12 % to 71 ± 11 % (+7 ± 6 %, p = 0.012). Brachial and aortic blood pressure showed no significant changes after six months. There was no correlation between LDL-C reduction and changes in vascular parameters.

CONCLUSIONS

Chronic PCSK9i therapy is associated with sustained improvements in endothelial function, arterial stiffness, and microvascular function independent from lipid lowering.

Incoherent Optical Fluctuation Flowmetry: A New Method for the Assessment of Foot Perfusion in Patients with Diabetes-Related Lower-Extremity Complications

(1) Background: To date, there are no studies evaluating the ability of the incoherent optical fluctuation flowmetry (IOFF) method to assess foot tissue perfusion. The aim of this study was to evaluate the correlation between perfusion values measured by IOFF and TcPO2 in patients with diabetes-related lower-extremity complications. (2) Methods: This was an observational, cross-sectional, two-center study. Diabetic patients with peripheral artery disease and/or diabetic foot ulcers were studied (n = 27, examinations were carried out on 54 legs). Perfusion in the foot tissues was assessed using TcPO2 (reference standard for this study) and the IOFF method. (3) Results: High correlation coefficients of all perfusion parameters measured by IOFF with TcPO2 (Rs 0.7 to 0.76) were shown. The study demonstrated that the IOFF method allows, with a sensitivity of 85.7% and a specificity of 90.0%, the identification of patients with a critical decrease in TcPO2 < 20 mmHg. (4) Conclusions: The high correlation of IOFF parameters with TcPO2 and the moderately high sensitivity and specificity in detecting patients with severe ischemia of foot tissues shows the promise of the method for assessing a tissue perfusion in patients with diabetes-related lower-extremity complications.