Enhancing walking performance in patients with peripheral arterial disease: An intervention with ankle-foot orthosis

Lower extremity peripheral artery disease (PAD) is a cardiovascular condition manifesting from narrowed or blocked arteries supplying the legs. Gait is impaired in patients with PAD. Recent evidence suggests that walking with carbon fiber ankle foot orthoses (AFOs) can improve patient mobility and delay claudication time. This study aimed to employ advanced biomechanical gait analysis to evaluate the impact of AFO intervention on gait performance among patients with PAD. Patients with claudication had hip, knee, and ankle joint kinetics and kinematics assessed using a cross-over intervention design. Participants walked over the force platforms with and without AFOs while kinematic data was recorded with motion analysis cameras. Kinetics and kinematics were combined to quantify torques and powers during the stance period of the gait cycle. The AFOs effectively reduced the excessive ankle plantar flexion and knee extension angles, bringing the patients' joint motions closer to those observed in healthy individuals. After 3 months of the AFO intervention, the hip range of motion decreased, likely due to changes occurring within the ankle chain. With the assistance of the AFOs, the biological power generation required from the ankle and hip during the push-off phase of walking decreased. Wearing AFOs resulted in increased knee flexor torque during the loading response phase of the gait. Based on this study, AFOs may allow patients with PAD to maintain or improve gait performance. More investigation is needed to fully understand and improve the potential benefits of ankle assistive devices.

Diagnosis of disease affecting gait with a body acceleration-based model using reflected marker data for training and a wearable accelerometer for implementation

This paper demonstrates the value of a framework for processing data on body acceleration as a uniquely valuable tool for diagnosing diseases that affect gait early. As a case study, we used this model to identify individuals with peripheral artery disease (PAD) and distinguish them from those without PAD. The framework uses acceleration data extracted from anatomical reflective markers placed in different body locations to train the diagnostic models and a wearable accelerometer carried at the waist for validation. Reflective marker data have been used for decades in studies evaluating and monitoring human gait. They are widely available for many body parts but are obtained in specialized laboratories. On the other hand, wearable accelerometers enable diagnostics outside lab conditions. Models trained by raw marker data at the sacrum achieve an accuracy of 92% in distinguishing PAD patients from non-PAD controls. This accuracy drops to 28% when data from a wearable accelerometer at the waist validate the model. This model was enhanced by using features extracted from the acceleration rather than the raw acceleration, with the marker model accuracy only dropping from 86 to 60% when validated by the wearable accelerometer data.

A comparison of the perceptions of wearing an ankle foot orthosis by individuals with peripheral artery disease according to their baseline-level of physical activity

INTRODUCTION

Peripheral artery disease (PAD) is a prevalent cardiovascular disease that limits an individual's ability to walk. One potential way to improve physical activity for patients with PAD is an ankle foot orthosis (AFO). Previous research has found that various factors may influence an individual's willingness to wear AFOs. However, one factor that has been understudied is an individual's baseline physical activity level prior to wearing AFOs. Therefore, the purpose of this study was to compare the perceptions of wearing AFOs for 3 months among individuals with PAD according to their baseline level of physical activity.

METHODS

Accelerometer-derived physical activity prior to AFO prescription was used to classify participants into either a higher or lower activity group. Semi-structured interviews were conducted at 1.5 and 3-months after wearing the AFOs to assess participants' perceptions of using the orthosis. Data were analyzed by a directed content analysis approach, then the percentage of respondents for each theme were calculated and compared between higher and lower activity groups.

FINDINGS

Several differences were found. Participants in the higher activity group more often reported positive impacts from wearing the AFOs. Additionally, participants who were in the lower activity group more often reported the AFOs caused physical pain while participants in the higher activity group more often reported the device was uncomfortable during daily activities.

CONCLUSION

Baseline physical activity levels may help to better understand barriers to wear and needed support to increase adherence to an AFO wear prescription, especially for patients with PAD with limited activity.

EFFECTS OF ASSISTIVE TENNIS SHOES ON GROUND REACTION FORCE FOR PATIENTS WITH PERIPHERAL ARTERY DISEASE DURING WALKING

Peripheral artery disease (PAD) is caused due to buildup of atherosclerotic plaques, typically in the leg arteries, preventing adequate blood circulation and ultimately claudication. A previous study showed that the vertical ground reaction force (VGRF) curve is significantly flatter in claudicating patients, resulting in a lower and less fluctuant center of mass when ambulating. Patients with PAD also demonstrate significantly decreased propulsion forces in the anterior– posterior direction. Assistive tennis shoes (carbon fiber: CF, and spring-loaded: SL) can potentially assist push-off by substituting for muscle forces using energy stored in a carbon fiber plate or metal spring within the shoe. This study aims to examine how the CF and SL shoes impact walking performance in patients with PAD. A total of ten patients with PAD performed a progressive treadmill test using a pressure-instrumented treadmill for each shoe type: i) standard shoes, ii) CF shoes, and iii) SL shoes. We calculated the peak VGRF for three subjects to date as an average of ten stance phases for the beginning of the walking condition (pain free condition). Preliminary results from three subjects showed that patients with PAD generated a greater peak VGRF wearing CF and SL shoes compared to normal shoes during the heel contact (normal: 0.97±0.10BW, CF: 1.03±0.08BW, and SL: 1.09±0.10BW) and push-off (normal: 0.97±0.06BW, CF: 0.99±0.04BW, and SL: 1.03±0.05BW). In future, we will calculate the VGRF for the remaining patients in pain free and pain conditions and conduct statistical analysis to identify significant differences among shoe types.

Joint Angle Variability Is Altered in Patients with Peripheral Artery Disease after Six Months of Exercise Intervention

Supervised exercise therapy (SET) is a conservative non-operative treatment strategy for improving walking performance in patients with peripheral artery disease (PAD). Gait variability is altered in patients with PAD, but the effect of SET on gait variability is unknown. Forty-three claudicating patients with PAD underwent gait analysis before and immediately after a 6-month SET program. Nonlinear gait variability was assessed using sample entropy, and the largest Lyapunov exponent of the ankle, knee, and hip joint angle time series. Linear mean and variability of the range of motion time series for these three joint angles were also calculated. Two-factor repeated measure analysis of variance determined the effect of the intervention and joint location on linear and nonlinear dependent variables. After SET, walking regularity decreased, while the stability remained unaffected. Ankle nonlinear variability had increased values compared with the knee and hip joints. Linear measures did not change following SET, except for knee angle, in which the magnitude of variations increased after the intervention. A six-month SET program produced changes in gait variability toward the direction of healthy controls, which indicates that in general, SET improved walking performance in individuals with PAD.

Assessing Wear Time and Perceptions of Wearing an Ankle Foot Orthosis in Patients with Peripheral Artery Disease

BACKGROUND

Peripheral artery disease (PAD) is a cardiovascular disease that effects patients' walking ability. An ankle foot orthosis (AFO) may improve patients' walking distances. Little research has explored if patients wear a prescribed AFO and their perceptions of wearing the device.

OBJECTIVE

To assess wear time of an AFO and explore perceptions of wearing the device in patients with peripheral artery disease.

DESIGN

Convergent mixed methods.

SETTING

The study was administered through a tertiary care medical center and the research subjects used the device in an outpatient setting in and out of their homes during their regular activities.

PARTICIPANTS

Patients were referred to the study by their vascular surgeon. Thirty-six patients, all older adult males, were enrolled in this study. Fourteen patients completed the study and 11 supplied sufficient accelerometer data.

INTERVENTIONS

An AFO was worn for 3 months. An accelerometer was placed on the AFO for 7 days at midpoint (1.5 months) and endpoint of the intervention (3 months) to assess wear time. Semi-structured interviews explored patients' perceptions of wearing the AFO.

MAIN OUTCOME MEASURE

The primary outcome measure was wear time measured objectively via accelerometer and subjectively via interview.

RESULTS

Patients (n = 14) wore the AFO around 8 hours/day. Most patients felt they wore the AFO a majority of the time. Patients reported barriers such as challenges wearing the AFO during daily household activities (using stairs, being on uneven terrain), discomfort, clothing or footwear issues, and driving challenges. Positive impacts of wearing the AFO were also reported, primarily the ability to walk further.

CONCLUSIONS

An AFO may be an acceptable therapeutic intervention to improve perceived walking performance in older adult males with PAD. Addressing patients' perceptions of the AFO and barriers to wear are essential to increasing the positive impact the device has on patients' ambulatory activity. This article is protected by copyright. All rights reserved.

Inflammatory Caspase Activity Mediates HMGB1 Release and Differentiation in Myoblasts Affected by Peripheral Arterial Disease

Introduction: We previously showed that caspase-1 and -11, which are activated by inflammasomes, mediate recovery from muscle ischemia in mice. We hypothesized that similar to murine models, inflammatory caspases modulate myogenicity and inflammation in ischemic muscle disease. Methods: Caspase activity was measured in ischemic and perfused human myoblasts in response to the NLRP3 and AIM2 inflammasome agonists (nigericin and poly(dA:dT), respectively) with and without specific caspase-1 or pan-caspase inhibition. mRNA levels of myogenic markers and caspase-1 were assessed, and protein levels of caspases-1, -4, -5, and -3 were measured by Western blot. Results: When compared to perfused cells, ischemic myoblasts demonstrated attenuated MyoD and myogenin and elevated caspase-1 mRNA. Ischemic myoblasts also had significantly higher enzymatic caspase activity with poly(dA:dT) (p < 0.001), but not nigericin stimulation. Inhibition of caspase activity including caspase-4/-5, but not caspase-1, blocked activation effects of poly(dA:dT). Ischemic myoblasts had elevated cleaved caspase-5. Inhibition of caspase activity deterred differentiation in ischemic but not perfused myoblasts and reduced the release of HMGB1 from both groups. Conclusion: Inflammatory caspases can be activated in ischemic myoblasts by AIM2 and influence ischemic myoblast differentiation and release of pro-angiogenic HMGB1. AIM2 inflammasome involvement suggests a role as a DNA damage sensor, and our data suggest that caspase-5 rather than caspase-1 may mediate the downstream mediator of this pathway.

Physical Activity Impacts Walking Distances and Energy Consumption of Patients with Peripheral Artery Disease

Lower extremity peripheral artery disease (PAD) is attributed to buildup of atherosclerotic plaques preventing adequate blood flow, leading to pain during walking, and ultimately physical inactivity. Normal day-to-day levels of physical activity may impact the distance a subject can walk before claudication pain onset, as well as their energy consumption capabilities. This study compared walking performance (initial claudication distance (ICD) and absolute claudication distance (ACD)), and energy consumption (EC) between active and inactive subjects with PAD. The distinction between groups was made using previous research that declared the average PAD patient walks 3586 steps/day. Ten subjects were classified as active (□3586 average steps/day) and sixteen participants as inactive (<3586 steps/day) based on a 7-day accelerometer measurement. The Gardner progressive treadmill test was used to asses ICD, ACD, and EC. EC was measured using a metabolic cart and calculated from the second minute of walking and the last minute prior to stopping due to claudication pain. The average ICD and ACD for the active group were 130.6±106.7 meters and 306.0±184.7 meters, respectively and 143.8±119.0 meters and 248.0±156.0 meters, respectively for the inactive group. The average EC for the second minute and last minute were 9.6±1.9 mlkg-1min-1 and 11.5±2.4 mlkg-1min-1 respectively for active group and 7.0±3.1 mlkg-1min-1 and 8.1±3.8 mlkg-1min-1 respectively for inactive group. The data suggests that the active group had better walking performance and greater energy consumption indicating increased efficiency of oxygen transport and extraction capability in the leg muscles.

Examining Ankle Foot Orthosis Wear Time in Patients With Peripheral Artery Disease

Peripheral artery disease (PAD) impacts over 8.5 million Americans and the prevalence of PAD increases with age. PAD restricts blood flow to the leg and its most common manifestation is claudication, a severe impairment of walking produced by ischemia-related, leg pain during exercise. An ankle foot orthosis (AFO) could improve these symptoms. To understand the potential impact of AFO usage, it is critical to determine wearability of the device in patients with PAD. The purpose of this study was to monitor wear time of an AFO and explore perceptions of the device. Participants (n=14) with PAD and claudication wore an AFO for three months. An accelerometer was placed directly on the AFO for 7 days and participants completed semi-structured interviews at midpoint (1.5 months) and post intervention (3 months). Based on accelerometer data at midpoint participants wore the AFO for an average of 4.9±2.3 out of 7 days and for an average of 7.5±4.2 hours each day. At post, participants wore the AFO for an average of 4.8±2.2 days for an average of 7.4±4.6 hours per day. In the interviews, almost all participants noted multiple barriers to wearing the AFO such as difficulty putting the AFO on and off, using stairs, walking on uneven ground, and driving. Our study found that participants wore the AFO ~7 hours/day but experienced barriers which may have limited their wear outside of these monitoring periods suggesting patients would wear an assistive device if design could be improved to address barriers.

Investigation of Roll-Over Characteristics in Healthy Old Individuals and Patients With Peripheral Artery Disease

Atherosclerotic blockages in the leg arteries, cause leg pain with ambulation (called claudication), impair gait and substantially reduce the walking ability of patients with peripheral artery disease (PAD). Ankle-foot orthoses are being developed and applied so patients can walk more and with less pain. Roll-over shape (ROS) is a potential design objective for such assistive devices. In the proposed work, we study roll-over characteristics in patients with PAD and healthy older subjects. Gait data of ten healthy older individuals (Age: 72.8 ± 5.5 years) and twenty patients with PAD (Age: 64.1 ± 6.6 years) were collected at self-selected walking speed. In patients with PAD, gait data were collected before the onset of pain and after claudication pain was induced. To generate ROS, the center of pressure data was transformed to the shank-based coordinate system and circular arcs were fit using an optimization program in MATLAB. Independent t-tests with Bonferroni corrections were used to separately compare roll-over radius differences (p<0.05) between healthy older to both walking conditions in patients with PAD. The mean roll-over radius was not significantly different between healthy older vs PAD pain-free (p=0.468) or PAD pain-induced (p=0.289) walking conditions. Our results indicate invariance of ROS radius in patients with PAD, which is consistent with previous literature showing general invariance of ROS in healthy young individuals. Previous biomechanical studies show gait kinematics and kinetics are more affected by PAD than by age. Future studies should focus on the potential adaptive mechanisms in patients with PAD achieving invariant ROS.

Novel open technique for repair of endograft migration

Widespread adoption of endovascular aneurysm repair has led to increased incidence of late complications, such as endograft migration. Treatment options have to be tailored to the patient's health, quality of proximal aorta, and extent of migration. Complete or partial endograft removal is associated with significant morbidity and mortality. We describe a case in which open repair with endograft preservation was employed, with the additional benefit of a sutured proximal anastomosis.

Abstract 138: Revascularization Improves the Hemodynamics, Function, and Myopathy of the Legs of Claudicating Patients

Introduction: Patients with claudication due to peripheral artery disease (PAD) have walking and quality of life (QOL) limitations associated with development of ischemic myopathy. Characteristics of PAD-related ischemic myopathy include myofiber degeneration, mitochondrial dysfunction, and oxidative damage. We hypothesize that revascularization operations improve lower extremity hemodynamics, function, and QOL with improvements in key indicators of PAD-related ischemic myopathy.

Methods: Patients undergoing open or endovascular revascularization were evaluated before and 6 months after intervention. QOL was assessed by Short Form-36 (SF-36) and Walking Impairment Questionnaire (WIQ). Walking performance was measured by six-minute walking distance (6MWD) and Gardner maximal Treadmill test (Peak Walking Time - PWT). Calf muscle biomechanics were measured by plantar flexor peak force (PFPF) and power generation (PFPG). Limb hemodynamics were measured with Ankle-Brachial Index (ABI) and myopathy was assessed via gastrocnemius biopsy. Myofibers were evaluated for mitochondrial function via respirometry while slide mounted specimens of the gastrocnemius were analyzed for biomarkers of morphology (myofiber cross-sectional area) and myofiber oxidative damage (carbonyl groups) by quantitative fluorescence microscopy.

Results: We recruited 52 patients who underwent 34 open and 18 endovascular revascularizations. Average score improved in 7 of 8 SF-36 (p<0.03) and 4 of 4 WIQ categories (p<0.001). PWT and 6MWD increased 305±75s (111.9%, p<0.001) and 62±17M (21.3%, p<0.001) respectively. PFPF and PFPG increased 9.8±3.1N (17.1%, p=0.001) and 1.6±0.08W/Kg (26.9%, p<0.001) respectively. ABI increased from 0.46±0.03 to 0.87±0.03 (90.4%, p<0.001). Myofiber cross-sectional area increased 458±216 μm 2 (11.1%, p<0.05). Complex I-mediated mitochondrial respiration (normalized to citrate synthase activity) improved 8.1±2.8 (15.4%, p<0.01). Oxidative damage observed as carbonyl groups was reduced 132±60 grayscale units (8.0%, p<0.05).

Conclusions: Revascularization operations improved the hemodynamics, QOL and leg function of PAD patients in association with improvement in PAD-related ischemic myopathy.

Abstract 334: Collateral Development in Swine after Ligation of Native Leg Arteries

Introduction: The development of collateral vasculature is a key mechanism compensating for arterial occlusions in patients with Peripheral Artery Disease (PAD). We aimed to examine the development of collateral pathways after ligation of native vessels in a porcine model of PAD.

Methods: Right hindlimb ischemia was induced in domestic swine (N=11, male, 26-57 kg) using two different versions of arterial ligation. Version 1 (N=6) consisted of ligation/division of the right external iliac, profunda femoral (RPFA) and superficial femoral arteries (RSFA). Version 2 (N=5) consisted of the ligation of Version 1 with additional ligation/division of the right internal iliac artery (RIIA). Development of collateral pathways was evaluated with standard angiography at baseline (prior to arterial ligation) and at termination (4-8 weeks later). Relative luminal diameter of the arteries supplying the ischemic right hindlimb were determined by 2D angiography, as percent of the size of the distal aortic diameter.

Results: The pathway connecting the RIIA to the RPFA and RSFA/popliteal artery of the ischemic limb was the dominant collateral pathway in version 1. Mean luminal diameter (± standard error) of the RIIA at termination increased by 39.4± 5.5% (P<0.01) compared to baseline. There were two co-dominant collateral pathways in version 2. The first pathway connected the common internal iliac trunk and left internal iliac artery to the reconstituted RIIA which then supplied the RPFA and RSFA/popliteal arteries. The second pathway connected the left profunda artery to the reconstituted RPFA. Mean diameter (± standard error) of the common internal iliac trunk and left profunda artery increased at termination by 23.7± 7.6% and 24.8± 7.4%, respectively (p < 0.05).

Conclusion: Two versions of hindlimb ischemia induction (right ilio-femoral artery ligation with and without right internal iliac artery ligation in swine produced differing collateral pathways along with changes to the diameter of the inflow vessels. Radiographic and anatomical data of the collateral formation in this porcine model has value in investigation of the pathophysiology of hindlimb ischemia, and assessment of angiogenic therapies as potential treatments for PAD.

Abstract 136: Near-Infrared Spectroscopy for Diagnosis and Characterization of Peripheral Artery Disease Severity

Background: Peripheral artery disease (PAD) frequently is undertreated. ABI is the standard for diagnosis of PAD but is limited in its ability to predict functional status and risk of disease progression. Previous work with Near-Infrared Spectroscopy (NIRS) has demonstrated impaired oxygen utilization in PAD muscle and may allow for improved diagnosis and stratification of disease severity. We hypothesize that exercise produces characteristic changes in lower-extremity muscle oxygenated heme percent (StO 2 ) which differentiates PAD from control and predicts PAD severity better than ABI.

Methods: We recruited 31 PAD subjects with intermittent claudication (IC) (ABI < 0.9) and 9 controls (ABI ≥ 0.9 and no IC). All subjects completed a Gardner maximal treadmill test. PAD subjects walked until IC was prohibitive (peak walking time, PWT) and controls walked for 540 seconds. StO 2 measurements were taken from the lateral gastrocnemius with the wireless MOXY NIRS monitor. StO 2 was documented at baseline, 60s, claudication onset time (COT), and PWT. For each subject, StO 2 values were expressed as percent of baseline to allow for comparison across subjects. Data were analyzed by student’s t-test and linear regression.

Results: Mean baseline StO 2 values were 46±11% and 58±17%, respectively, for PAD and control subjects. Among controls, StO 2 dropped below baseline at 140±101s whereas PAD subjects dropped below baseline at 6±10s (P<0.001). PAD StO 2 s at 60s, COT, and PWT were compared to control StO 2 s at the corresponding time points. PAD patients’ StO 2 at 60s, COT, and PWT were 65.2±37.9% (n=31), 66.4±35.5% (n=31), and 73.2±26.0% (n=25) lower than controls, respectively (P < 0.001). PAD subjects were separated into tertiles of PWT. Relative to baseline, StO 2 decreased 84.2±18.4% (n=11) in the lowest tertile compared to 29.8±30.6% (n=10) in the highest tertile (P<0.05). Percent decrease in StO 2 at 60s correlated to PWT (R 2 =0.56) in contrast to ABI (R 2 =0.018).

Conclusion: During exercise, PAD patients exhibited a characteristic change in StO 2 . In contrast to ABI, StO 2 predicted PAD-related exercise limitation. These data suggest NIRS in conjunction with traditional methods could be used to guide diagnostic and treatment decisions.

Abstract 340: Microvascular Pathology in Peripheral Artery Disease

Background: Peripheral Artery Disease (PAD) is caused by atherosclerotic narrowing of arteries supplying the legs. PAD-induced myopathy is characterized by myofiber degeneration and progressive fibrosis. Qualitative histological review suggests pathological changes in the microvasculature of PAD muscle, in association with advancing fibrosis. We tested the hypothesis that microvessel architecture, pericyte coverage, and collagen profiles systematically change with advancing disease and are consistent with advancing microvascular pathology.

Methods: Biopsies of PAD patients at Fontaine Stage II (n=15) and IV (n=16), and controls (n=15) were labeled with antibodies specific for Col I, Col IV, αSMA, or CD31 and analyzed by quantitative wide-field, fluorescence microscopy. Thickness of the basement membrane (BM), peri-microvascular Col I density, and BM lumen diameter were measured. Pericytes were identified by abluminal location within the microvascular BM and αSMA + labeling. Group differences were tested by ANOVA and a post hoc pairwise T Test with Bonferroni correction. Correlations were determined by linear regression analysis.

Results: Thickness of the BM was greater in Stage II patients (1.58 μm) compared to controls (1.42 μm) (p<0.043) and in Stage IV (1.75 μm) compared to Stage II patients (p<0.021). Microvascular BM lumen diameter was increased (p<0.001) in Stage IV patients (3.97 μm) compared to control (3.25 μm) and Stage II patients (3.29 μm). Thickened PAD microvessels had greater pericyte coverage than control microvessels. BM thickness correlated positively with microvascular BM lumen diameter (R 2 = 0.513, p<0.001). Peri-microvascular Col I deposition correlated positively with microvascular lumen diameter (R 2 = 0.162, p=0.006), and was greater in Stage IV compared to Stage II patients (p=0.040).

Conclusions: Increased perivascular Col I deposition, BM thickening, and BM lumen diameter represent advancing microvascular disease in PAD patients. Pericytes, which deposit BM collagen, are more abundant in thickened microvessels. Pericyte replication and secretion of Col IV may be determining factors in the microvascular pathology of PAD muscle.

Premature aortic smooth muscle cell differentiation contributes to matrix dysregulation in Marfan Syndrome

Thoracic aortic aneurysm and dissection are life-threatening complications of Marfan syndrome (MFS). Studies of human and mouse aortic samples from late stage MFS demonstrate increased TGF-β activation/signaling and diffuse matrix changes. However, the role of the aortic smooth muscle cell (SMC) phenotype in early aneurysm formation in MFS has yet to be fully elucidated. As our objective, we investigated whether an altered aortic SMC phenotype plays a role in aneurysm formation in MFS. We describe previously unrecognized concordant findings in the aortas of a murine model of MFS, mgR, during a critical and dynamic phase of early development. Using Western blot, gelatin zymography, and histological analysis, we demonstrated that at postnatal day (PD) 7, before aortic TGF-β levels are increased, there is elastic fiber fragmentation/disorganization and increased levels of MMP-2 and MMP-9. Compared to wild type (WT) littermates, aortic SMCs in mgR mice express higher levels of contractile proteins suggesting a switch to a more mature contractile phenotype. In addition, tropoelastin levels are decreased in mgR mice, a finding consistent with a premature switch to a contractile phenotype. Proliferation assays indicate a decrease in the proliferation rate of mgR cultured SMCs compared to WT SMCs. KLF4, a regulator of smooth muscle cell phenotype, was decreased in aortic tissue of mgR mice. Finally, overexpression of KLF4 partially reversed this phenotypic change in the Marfan SMCs. This study indicates that an early phenotypic switch appears to be associated with initiation of important metabolic changes in SMCs that contribute to subsequent pathology in MFS.

Abstract 114: Calf Muscle Oxygen Saturation During Standardized Treadmill Testing in Patients With Intermittent Claudication

Objectives: Leg muscle hypoxia during walking is believed to be a key mechanism underlying the exercise intolerance of claudicating patients but detailed data on the changes exercise produces in the kinetics of leg muscle oxygenation are limited. Our objective was to record the calf muscle oxygen saturation (MO 2 S) at rest, during treadmill exercise and during recovery from exercise in patients with chronic claudication.

Methods: We recruited 19 claudicating patients. The MO 2 S of the gastrocnemius was recorded with the Moxy near-infrared spectroscopy monitor (Hutchinson, MN). We measured resting MO 2 S for a period of three minutes and then performed a Gardner, standardized treadmill test. We recorded claudication onset time (COT) and peak walking time. We also measured the MO 2 S recovery for 30 minutes following the end of the TT or until muscle saturation reached a steady state.

Results: Table I summarizes our results. Patients started experiencing a decrease in their MO 2 S 18.8 sec after initiation of TT; approximately 28 steps covering 16.8 meters. COT occurred when calf MO 2 S had dropped to 23.7%. Patients reached their minimum (14.1%) MO 2 S, 340.5 sec into the TT. During the post-TT recovery period, MO 2 S rebounded initially to 65.1% at 689.4 sec and 407.1 sec later it declined to a steady-state level of 56.3%, both above the pre-TT baseline reading. This relative hyperoxic state persisted for the duration of the post-exercise recording period (≥30 min).

Conclusions: Our study objectively demonstrates considerable, walking-induced changes in MO 2 S in patients with claudication. During walking, MO 2 S drops quickly and the calf muscles experience substantial hypoxia while after the end of walking, MO 2 S rebounds above the baseline state and the leg muscles remain relatively hyperoxic beyond 30 min. This study provides much needed data concerning the kinetic patterns of muscle oxygenation claudicating patients experience in their everyday lives.

Abstract 115: Microvascular Response to Ramipril in Peripheral Artery Disease

Background: The myopathy of Peripheral Artery Disease (PAD), a consequence of ischemia caused by atherosclerotic plaques in arteries supplying the legs, is characterized by myofiber degeneration and fibrosis of the vascular walls and extramyofiber matrix. In association with fibrosis we have found a robust expression of the profibrotic cytokine TGFβ1 in vascular smooth muscle cells. Additionally, we have observed microvascular endothelial “swelling” in PAD muscle. Published data indicate that inhibitors of the angiotensin system reduce fibrosis in multiple organ systems and improve walking performance, in diverse patient populations. We hypothesize that “swelling” of microvasculature endothelial cells represents abnormal accumulation of basement membrane Collagen Type IV (Col-IV) and that treatment with Ramipril will improve the microvasculature.

Methods and Results: Gastrocnemius biopsies of PAD patients at Fontaine Stage II (N=5) before and after six months of Ramipril intervention and control patients (N=4) were labeled with an antibody specific for Col-IV. Images were acquired with an automated wide-field microscope and then processed with Image Pro Plus® and AutoQuant® deconvolution software. We used Col IV label to measure wall thickness and lumen diameter of 230 to 360 microvessels per patient, with a custom MatLab program based on the Expectation Maximization algorithm coupled with a Gaussian Mixture Model. Microvessel wall thickness was significantly greater (p < 0.04) in PAD patients before (1.54 ± 0.04 μ) and after (1.61 ± 0.06 μ) Ramipril treatment compared to control (1.42 ± 0.02). Lumen diameter was significantly greater (p < 0.02) in Post-Ramipril (3.49 ± 0.04 μ) compared to Pre-Ramipril (3.18 ± 0.08 μ) and control (3.00 ± 0.11 μ) patients.

Conclusions: The increase of microvessel lumen diameter with Ramipril treatment is expected to increase microvascular perfusion and thereby improve walking distance. Our study will be expanded to increase cohort size and evaluate the association of microvascular measurements with microperfusion determined by Contrast Enhanced Ultrasonography and with walking performance.

Abstract 116: Revascularization but Not Supervised Exercise Therapy Prevents Progression of Fibrosis in the Gastrocnemius of Patients With Peripheral Artery Disease While Improving Limb Function

Introduction: Patients with peripheral artery disease (PAD) develop myofiber degeneration and fibrosis in their ischemic lower extremities, along with limb dysfunction. Walking performance improves with revascularization and exercise therapy, but effects on the myopathy are unknown. We previously showed fibrosis progresses with PAD and positively correlates with expression of vascular transforming growth factor-beta 1 (TGF-β1), a cytokine that stimulates collagen deposition.

Hypothesis: We hypothesize that revascularization (RVS) and supervised exercise therapy (EXE) improve limb function in association with improved TGF-β1 dependent fibrosis.

Methods: Gastrocnemius biopsies were collected from PAD patients (Fontaine Stage II; N=56) at baseline and 6 months after RVS (N=20), EXE (N=19), or no intervention (CTL; N=17). TGF-β1 expression was measured as grey scale units (gsu) by quantitative fluorescence microscopy of paraffin-embedded gastrocnemius sections. Collagen abundance was measured as optical density by quantitative multi-spectral bright-field microscopy of Masson Trichrome stained paraffin sections. Six Minute Walking Distance (SMWD), in meters, and Peak Walking Time (PWT), in seconds, were determined at baseline and 6 months. Relationships among TGF-β1, collagen, and limb function were assessed.

Results: TGF-β1 expression and collagen density increased in CTL and EXE but not RVS patients. SMWD and PWT increased among RVS patients. PWT but not SMWD increased among EXE patients. SMWD and PWT were unchanged among CTL patients. The data are summarized in Table 1.

Conclusions: RVS and EXE improved walking performance of patients with PAD, but only RVS prevented progression of fibrosis in the gastrocnemius of these patients. Over the same 6-month period, fibrosis increased in CTL muscle but was not sufficient to alter walking performance. The data suggest that benefits to the PAD leg may be greater with RVS compared to EXE.

Spontaneous and coherent anti-Stokes Raman spectroscopy of human gastrocnemius muscle biopsies in CH-stretching region for discrimination of peripheral artery disease

Peripheral Artery Disease (PAD) is a common manifestation of atherosclerosis, characterized by lower leg ischemia and myopathy in association with leg dysfunction. In the present study, Spontaneous and coherent anti-Stokes Raman scattering (CARS) spectroscopic techniques in CH-stretching spectral region were evaluated for discriminating healthy and diseased tissues of human gastrocnemius biopsies of control and PAD patients. Since Raman signatures of the tissues in the fingerprint region are highly complex and CH containing moieties are dense, CH-stretching limited spectral range was used to classify the diseased tissues. A total of 181 Raman spectra from 9 patients and 122 CARS spectra from 12 patients were acquired. Due to the high dimensionality of the data in Raman and CARS measurements, principal component analysis (PCA) was first performed to reduce the dimensionality of the data (6 and 9 principal scores for Raman and CARS, respectively) in the CH-stretching region, followed by a discriminant function analysis (DFA) to classify the samples into different categories based on disease severity. The CH2 and CH3 vibrational signatures were observed in the Raman and CARS spectroscopy. Raman and CARS data in conjunction with PCA-DFA analysis were capable of differentiating healthy and PAD gastrocnemius with an accuracy of 85.6% and 78.7%, respectively.

Patient demographics and cardiovascular risk factors differentially influence geometric remodeling of the aorta compared with the peripheral arteries

BACKGROUND

Detailed knowledge of the dimensions and shape of the main arteries of the body and how they change with age and disease is important for understanding arterial pathophysiology and improving minimally invasive devices to treat arterial diseases. Our goal was to describe and compare geometric remodeling of the aorta and peripheral arteries in the context of patient demographics and cardiovascular risk factors.

METHODS

Three-dimensional reconstructions of computed tomography angiography scans were performed in 122 subjects 5-93 years of age (mean 47 ± 24 years, 64 M/58 F). Best-fit arterial diameters, lengths, and tortuosity for the principle named arteries in the chest, abdomen, pelvis, and upper thigh were measured, and multiple linear regression analysis was performed to examine how these morphologic parameters associate with patient demographics and risk factors.

RESULTS

Large elastic arteries increased their diameter, length, and tortuosity with age, whereas muscular arteries primarily became more tortuous. Demographics and risk factors explained >70% of the variation in diameters of the abdominal aorta, paravisceral aorta, and the aortic arch; and >75% of variation in tortuosity from the profunda femoris to the brachiocephalic artery. Male sex, larger body mass index, and hypertension contributed to larger diameters, whereas the presence of diabetes was associated with somewhat-straighter arteries. Overall, the effects of cardiovascular risk factors on geometric remodeling were small compared with those of demographics.

CONCLUSION

The geometry of the vascular tree is greatly affected by aging, demographics, and some risk factors. Elastic and muscular arteries remodel differently, possibly as the result of differences in their microstructure.

Abstract 713: Effects of Demographics and Clinical Risk Factors on Human Femoropopliteal Artery Histopathology

Introduction: Disease of the femoropopliteal artery (FPA) is associated with significant morbidity and quality of life impairment. End-stage lesions may be too advanced to determine how demographics and clinical risk factors impact arterial wall damage and lesion development; therefore we investigated the influence of these patient characteristics on various stages of human FPA histopathology.

Methods: FPAs were obtained from 14-80 year-old human tissue donors ( n =120). Proximal segments of the arteries were mechanically tested and labeled with Verhoeff-Van Gieson stains. FPA intimal-medial damage severity was assessed and correlated with histology, mechanical properties, subject demographics, risk factors, and physiological stresses and stretches using Pearson correlation r with two-tailed significance levels.

Results: Age correlated strongest ( r =0.664, p<0.01) with the degree of FPA intimal-medial damage, explaining 50% of the variation alone. Primarily due to medial calcification, more damaged FPAs were stiffer and demonstrated lower physiological circumferential stretch ( r =-0.510, p<0.01), circumferential stress and longitudinal stress ( r =-0.355, r =-0.379, p<0.01). More damage was associated with larger arterial radii ( r =0.470, p<0.01), thickened arterial walls ( r =0.238, p<0.01), decreased in situ longitudinal pre-stretch ( r =-0.537, p<0.01), less elastin in the arterial wall ( r =-0.432, p<0.01), thinner individual elastin fibers ( r =-0.571, p<0.01), and thinner, less dense, and more discontinuous external elastic laminae ( r =-0.252, r =-0.456, r =0.588, p<0.01). Damage was positively associated with male gender ( r =0.265, p<0.01), higher BMI ( r =0.224, p=0.01), hypertension ( r =0.266, p<0.01), diabetes ( r =0.265, p<0.01) and coronary artery disease ( r =0.375, p<0.01), but not with dyslipidemia ( r =0.117, p=0.161) or smoking history ( r =0.041, p=0.626).

Conclusions: More severely damaged FPAs demonstrate elastin loss, medial calcification and increased stiffness compared to less damaged arteries. FPA damage correlates with most classical cardiovascular risk factors, but not with dyslipidemia or tobacco history, suggesting possible unique pathophysiological mechanisms that require further investigation.

Abstract 290: Lower Limb Revascularization of Patients with Peripheral Artery Disease Reduces Human Enterovirus Infection of the Gastrocnemius

Introduction: Peripheral artery disease (PAD), caused by obstruction of arteries supplying the lower extremities, is characterized by leg muscle degeneration. Recently, we showed that infectious human enterovirus (HEV), which has been implicated in other myodegenerative diseases, is present in ischemic muscle of PAD patients and that viral copy numbers correlate with disease severity.

Hypothesis: We tested the hypothesis that prevalence of infectious HEV and viral copy number in the gastrocnemius of patients with PAD decrease in response to revascularization.

Methods: Gastrocnemius biopsies were collected from controls (N=14) and from PAD patients (N=17), before and after revascularization. Biopsies were examined for the presence of HEV RNA, viral capsid protein, viral RNA copy number, and viral infectivity and for viral sub-genotype.

Results: HEV RNA was detected in biopsies of 65% (11/17) of PAD patients and in none of the controls. After revascularization, the gastrocnemius of 5 patients who were HEV positive before surgery no longer harbored detectable virus. The prevalence of HEV infection was reduced from 65% (11/17 patients) before surgery to 35% (6/17 patients) after surgery. Positive-strand viral RNA copy numbers were decreased significantly after revascularization. Mean positive-strand copy number (average 10 2.61 copies/mg muscle wet weight) in post-surgical biopsies that were HEV-positive were lower (p<0.001) compared to mean copy number (average 10 5.46 copies/mg muscle wet weight) in pre-surgical biopsies that were HEV-positive. Copy numbers of negative-strand (template) viral RNA were also decreased after revascularization. Viral replication was confirmed by detection of negative-strand viral RNA in all specimens positive for HEV. Cultures of HeLa and human skeletal muscle cells treated with muscle homogenates showed HEV replication and the presence of HEV capsid protein. By sequence analysis, HEV in PAD muscle exhibited 97% homology with Coxsackievirus B1.

Conclusion: Our data introduce HEV infection as a potential mechanism for degeneration of ischemic muscle in PAD patients and demonstrate that revascularization of PAD patients reduces both prevalence of HEV infection and viral copy number in the gastrocnemius.

Neuropeptide Y receptors in carotid plaques of symptomatic and asymptomatic patients: effect of inflammatory cytokines

AIMS

Cytokines released by the immune cells at the site of plaque milieu induce smooth muscle cell apoptosis to promote plaque instability. But, neuropeptide Y (NPY), a pleotropic factor, may modulate the effects of cytokines in atherosclerotic plaques of patients with carotid stenosis. Our aim was to investigate the relative expression of NPY-Y1, NPY-Y2 and NPY-Y5 receptors on carotid plaque vascular smooth muscle cells (pVSMCs) of symptomatic (S) and asymptomatic (AS) patients and examine the effect of inflammatory cytokines on the expression of NPY receptors, that may attenuate plaque rupture.

METHODS AND RESULTS

In healthy carotid artery, there were significantly increased immunopositivity and increased mRNA transcripts of NPY-Y1 and NPY-Y5 receptors in thin sections and isolated VSMCs, respectively, compared to S and AS plaques. However, the NPY-Y2 expression was higher in S and AS pVSMCs than controls. Stimulation of the cells with TNF-α, IL-12 or IFN-γ (50 ng/ml) decreased mRNA transcripts of NPY-Y1 and NPY-Y5 and increased NPY-Y2 mRNAs in VSMCs of healthy carotid artery. The effect of the cytokines on mRNA transcripts of NPY-Y5 and NPY-Y2 in pVSMCs of S and AS patients was similar to healthy VSMCs, but with variable effect on NPY-Y1.

CONCLUSION

Increased expression of NPY-Y2 receptors in symptomatic pVSMCs than in healthy and asymptomatic subjects suggests a potential role of NPY-Y2 in plaque instability. This is further supported by the pronounced effect of atheroma-associated cytokines to increase NPY-Y2 mRNA transcripts in pVSMCs of patients with carotid stenosis.

Bilateral claudication results in alterations in the gait biomechanics at the hip and ankle joints

Claudication is the most common symptomatic manifestation of peripheral arterial disease (PAD), producing significant ambulatory compromise. The purpose of this study was to use advanced biomechanical gait analysis to determine the gait alterations occurring in claudicating patients both before and after onset of claudication pain in their legs. Hip, knee, and ankle joint moments were measured in claudicating patients (age: 64.46+/-8.47 years; body mass: 80.70+/-12.64kg; body height: 1.72+/-0.08m) and were compared to gender-age-body mass-height-matched healthy controls (age 66.27+/-9.22 years; body mass: 77.89+/-10.65kg; body height: 1.74+/-0.08m). The claudicating patients were evaluated both before (pain-free (PF) condition) and after (pain condition) onset of claudication pain in their legs. Thirteen symptomatic PAD patients (26 claudicating limbs) with bilateral intermittent claudication (IC) and 11 healthy controls (22 control limbs) were tested during level walking at their self-selected speed. Compared to controls, PAD hip and ankle joints demonstrated significant angular kinematics and net internal moment changes. Alterations were present both in PF and pain conditions with several of them becoming worse in the pain condition. Both PF and pain conditions resulted in significantly reduced peak hip extensor moment (5.62+/-1.40 and 5.63+/-1.33% BWxBH, respectively) during early stance as compared to controls (7.53+/-1.16% BWxBH). In the pain condition, PAD patients had a significantly reduced ankle plantar flexor moment (7.56+/-1.41% BWxBH) during late stance as compared to controls (8.65+/-1.27% BWxBH). Furthermore, when comparing PF to pain conditions, there was a decreased peak plantar flexor moment (PF condition: 8.23+/-1.37 vs. pain condition: 7.56+/-1.41% BWxBH) during late stance. The findings point to a weakness in the posterior compartment muscles of the hip and calf as being the key factor underlying the PAD gait adaptations. Our findings establish a detailed baseline description of the changes present in PAD patient's joint angles and moments during walking. Since IC is primarily a gait disability, better understanding of the abnormalities in joint and muscle function will enhance our understanding of the gait impairment and may lead to novel, gait-specific treatments.

Successful hematopoietic stem-cell transplantation in multicentric Castleman disease complicated by POEMS syndrome

A 39-year-old male presented with pedal edema, pleural effusion, splenomegaly, and generalized lymphadenopathy. Serum protein electrophoresis demonstrated the presence of a monoclonal protein. Histological examination of the spleen following splenectomy showed multifocal vascular proliferation and angiovascular lesions consistent with multicentric Castleman disease. He was treated with steroids and rituximab, but without improvement. The patient was found to have portal venous thrombosis and lower extremity arterial thrombosis. He then received combination chemotherapy with cyclophosphamide and mitoxantrone but developed a severe inflammatory polyneuropathy that left him disabled and wheelchair-bound. A diagnosis of multicentric Castleman disease with POEMS syndrome was made, and he then received high-dose chemotherapy with melphalan followed by autologous peripheral blood stem-cell transplantation. Following transplantation, his nerve conduction studies improved and his serum protein electrophoresis normalized. He is currently ambulatory and does not need wheelchair assistance. Hematopoietic stem-cell transplantation may be a treatment option for patients with multicentric Castleman disease and POEMS syndrome.

Limb loss following lower extremity arterial trauma: what can be done proactively?

We performed a retrospective review of patients admitted to two Level I trauma centres over a 15-year period with arterial injuries (excluding primary amputations). Preoperative factors analysed included mechanism of injury, site and type of arterial and venous injury and repair, time to operating room, initial blood pressure, evidence of ipsilateral limb fracture and/or extensive tissue damage, status of preoperative pulses and angiographic data. One hundred and fifty-one arterial injuries were treated (80 penetrating). Overall mortality was 10 (6.6%) and limb loss 16 (10.6%). Only two factors that might possibly be modified by specific interventions were noted. The incidence of limb loss was higher in patients who developed compartment syndrome (41% versus 7% without, P=0.003) and in those who did not receive intra- or immediately postoperative anticoagulation (15% without versus 3% with, P=0.02). Unfortunately, no factor was found that reliably predicted the risk of compartment syndrome. In addition, patients who did not receive peri-operative anticoagulation were more severely injured than those that did were. Despite this, there were no bleeding complications associated with anticoagulation. These findings suggest that the primary interventions that may improve limb salvage include liberal use of fasciotomy (recognising that any patient may require this) as well as early use of anticoagulation.