Calf muscle hemoglobin oxygen saturation characteristics and exercise performance in patients with intermittent claudication

Effects of Long-Term Home Exercise in Participants With Peripheral Artery Disease

Background This randomized controlled trial compared long-term changes in peak walking time (PWT) and exercise time-to-minimum calf muscle oxygen saturation (StO2) in symptomatic participants with peripheral artery disease following a long-term home exercise program (HEP), a short-term supervised exercise therapy (SET) program that transitioned to a long-term HEP (SET/HEP), and a control intervention. Methods and Results For the first 3 months, HEP and SET/HEP groups performed intermittent walking to mild-to-moderate claudication pain, whereas the control group performed light resistance training. For the subsequent 15 months, the HEP group continued their exercise program, the SET/HEP group transitioned from SET to the HEP program, and the control group transitioned to only receive walking advice. PWT increased significantly from baseline to month 18 in the HEP group (408±279 meters to 814±393 meters, P<0.001) and in the SET/HEP group (457±288 meters to 818±313 meters, P<0.001). Exercise time-to-minimum calf muscle StO2 increased significantly from baseline to month 18 in the HEP group (238±241 seconds to 497±485 seconds, P<0.05) and in the SET/HEP group (296±289 seconds to 620±450 seconds, P<0.001). These changes in PWT and exercise time-to-minimum calf muscle StO2 were greater than in the control group (P<0.001 and P<0.01, respectively). Additionally, the change in exercise time-to-minimum calf muscle StO2 was correlated with the change in PWT in both exercise groups combined (r=0.601, P=0.0015). Conclusions Long-term HEP and SET/HEP were efficacious in improving PWT and exercise time-to-minimum calf muscle StO2 in symptomatic participants with peripheral artery disease, and these changes were correlated with each other. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT00618670.

Maximal calf conductance is associated with 6-minute walk distance in participants with and without peripheral artery disease

INTRODUCTION

The aims were (a) to compare the maximal calf conductance and 6-minute walk distance of participants with and without peripheral artery disease (PAD) and claudication, (b) to determine whether maximal calf conductance was more strongly associated with 6-minute walk distance in participants with PAD than in the controls, and (c) to determine whether this association was significant in participants with PAD after adjusting for ABI, as well as for demographic, anthropometric, and comorbid variables.

METHODS

Participants with PAD (n = 633) and without PAD (n = 327) were assessed on maximal calf conductance using venous occlusion plethysmography, and on 6-minute walk distance. Participants were further characterized on ABI, and on demographic, anthropometric, and comorbid variables.

RESULTS

The PAD group had lower maximal calf conductance than the control group (0.136 ± 0.071 vs 0.201 ± 0.113 mL/100 mL/min/mmHg, p < 0.001). Additionally, the PAD group had a lower 6-minute walk distance (375 ± 98 m vs 480 ± 107 m, p < 0.001). Maximal calf conductance was positively associated with 6-minute walk distance in both groups (p < 0.001) and was more strongly associated in the PAD group (p < 0.001). In adjusted analyses, maximal calf conductance remained positively associated with 6-minute walk distance in the PAD group (p < 0.001) and in the control group (p < 0.001).

CONCLUSIONS

Participants with PAD and claudication had impaired maximal calf conductance and a lower 6-minute walk distance than those without PAD, and maximal calf conductance was positively and independently associated with 6-minute walk distance within each group before and after adjusting for ABI, and for demographic, anthropometric, and comorbid variables.

Muscle Oxygenation and Microvascular Reactivity Across Different Stages of CKD: A Near-Infrared Spectroscopy Study

RATIONALE & OBJECTIVE

Previous studies in chronic kidney disease (CKD) showed that vascular dysfunction in different circulatory beds progressively deteriorates with worsening CKD severity. This study evaluated muscle oxygenation and microvascular reactivity at rest, during an occlusion-reperfusion maneuver, and during exercise in patients with different stages of CKD versus controls.

STUDY DESIGN

Observational controlled study.

SETTING & PARTICIPANTS

90 participants (18 per CKD stage 2, 3a, 3b, and 4, as well as 18 controls).

PREDICTOR

CKD stage.

OUTCOME

The primary outcome was muscle oxygenation at rest. Secondary outcomes were muscle oxygenation during occlusion-reperfusion and exercise, and muscle microvascular reactivity (hyperemic response).

ANALYTICAL APPROACH

Continuous measurement of muscle oxygenation [tissue saturation index (TSI)] using near-infrared spectroscopy at rest, during occlusion-reperfusion, and during a 3-minute handgrip exercise (at 35% of maximal voluntary contraction). Aortic pulse wave velocity and carotid intima-media thickness were also recorded.

RESULTS

Resting muscle oxygenation did not differ across the study groups (controls: 64.3% ± 2.9%; CKD stage 2: 63.8% ± 4.2%; CKD stage 3a: 64.1% ± 4.1%; CKD stage 3b: 62.3% ± 3.3%; CKD stage 4: 62.7% ± 4.3%; P=0.6). During occlusion, no significant differences among groups were detected in the TSI occlusion magnitude and TSI occlusion slope. However, during reperfusion the maximum TSI value was significantly lower in groups of patients with more advanced CKD stages compared with controls, as was the hyperemic response (controls: 11.2%±3.7%; CKD stage 2: 8.3%±4.6%; CKD stage 3: 7.8%±5.5%; CKD stage 3b: 7.3%±4.4%; CKD stage 4: 7.2%±3.3%; P=0.04). During the handgrip exercise, the average decline in TSI was marginally lower in patients with CKD than controls, but no significant differences were detected across CKD stages.

LIMITATIONS

Moderate sample size, cross-sectional evaluation.

CONCLUSIONS

Although no differences were observed in muscle oxygenation at rest or during occlusion, the microvascular hyperemic response during reperfusion was significantly impaired in CKD and was most prominent in more advanced CKD stages. This impaired ability of microvasculature to respond to stimuli may be a crucial component of the adverse vascular profile of patients with CKD and may contribute to exercise intolerance.

Association Between Meeting Physical Activity Time-Intensity Guidelines With Ambulation, Quality of Life, and Inflammation in Claudication

PURPOSE

The aim of this investigation was to determine if meeting the 2018 physical activity (PA) time-intensity guidelines was associated with better ambulatory function, health-related quality of life (HRQoL), vascular function, and inflammation than failing to meet the guidelines in patients with peripheral artery disease and claudication. Second, we determined the optimal number of total steps/d and steps taken at moderate cadence needed to meet the PA time-intensity guidelines.

METHODS

Five hundred seventy-two patients were assessed on daily ambulatory activity for 1 wk with a step activity monitor, and were grouped according to whether they achieved <150 min/wk of moderate-intensity PA (group 1 = do not meet guidelines; n = 397) or whether they were above this threshold (group 2 = meet guidelines; n = 175).

RESULTS

Treadmill peak walking time (mean ± SD) was higher ( P < .001) in group 2 (709 ± 359 sec) than in group 1 (427 ± 281 sec). The physical function HRQoL score was higher ( P < .001) in group 2 (61 ± 22%) than in group 1 (44 ± 21%). High-sensitivity C-reactive protein was lower ( P < .001) in group 2 (3.6 ± 4.5 mg/L) than in group 1 (5.9 ± 6.1 mg/L). Finally, ≥7675 total steps/d and ≥1660 steps/d at moderate cadence were optimal thresholds associated with meeting PA guidelines.

CONCLUSIONS

Patients with claudication who meet the 2018 PA time-intensity guidelines for US adults had better ambulation, HRQoL, and vascular outcomes than those who failed to meet the PA guidelines. Patients with claudication best achieved the PA time-intensity guidelines by taking ≥7675 total steps/d, and ≥1660 steps/d at a moderate cadence.

Microvascular dysfunction and neurovascular uncoupling are exacerbated in peripheral artery disease, increasing the risk of cognitive decline in older adults

Peripheral artery disease (PAD) is a vascular pathology with high prevalence among the aging population. PAD is associated with decreased cognitive performance, but the underlying mechanisms remain obscure. Normal brain function critically depends on an adequate adjustment of cerebral blood supply to match the needs of active brain regions via neurovascular coupling (NVC). NVC responses depend on healthy microvascular endothelial function. PAD is associated with significant endothelial dysfunction in peripheral arteries, but its effect on NVC responses has not been investigated. This study was designed to test the hypothesis that NVC and peripheral microvascular endothelial function are impaired in PAD. We enrolled 11 symptomatic patients with PAD and 11 age- and sex-matched controls. Participants were evaluated for cognitive performance using the Cambridge Neuropsychological Test Automated Battery and functional near-infrared spectroscopy to assess NVC responses during the cognitive n-back task. Peripheral microvascular endothelial function was evaluated using laser speckle contrast imaging. We found that cognitive performance was compromised in patients with PAD, evidenced by reduced visual memory, short-term memory, and sustained attention. We found that NVC responses and peripheral microvascular endothelial function were significantly impaired in patients with PAD. A positive correlation was observed between microvascular endothelial function, NVC responses, and cognitive performance in the study participants. Our findings support the concept that microvascular endothelial dysfunction and neurovascular uncoupling contribute to the genesis of cognitive impairment in older PAD patients with claudication. Longitudinal studies are warranted to test whether the targeted improvement of NVC responses can prevent or delay the onset of PAD-associated cognitive decline.NEW & NOTEWORTHY Peripheral artery disease (PAD) was associated with significantly decreased cognitive performance, impaired neurovascular coupling (NVC) responses in the prefrontal cortex (PFC), left and right dorsolateral prefrontal cortices (LDLPFC and RDLPFC), and impaired peripheral microvascular endothelial function. A positive correlation between microvascular endothelial function, NVC responses, and cognitive performance may suggest that PAD-related cognitive decrement is mechanistically linked, at least in part, to generalized microvascular endothelial dysfunction and subsequent impairment of NVC responses.

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.

LIGHT AND MODERATE INTENSITY PHYSICAL ACTIVITY ARE ASSOCIATED WITH BETTER AMBULATION, QUALITY OF LIFE, AND VASCULAR MEASUREMENTS IN PATIENTS WITH CLAUDICATION

OBJECTIVES

To determine whether patients with claudication who reported performing either light-intensity physical activity (LPA) or moderate-to-vigorous intensity physical activity (MVPA) had higher levels of objectively-determined physical activity, and better physical function, health-related quality of life (HRQoL), and vascular measures, consisting of exercise time to minimum calf muscle oxygen saturation (StO₂) and high-sensitivity C-reactive protein, than patients who reported being physically sedentary.

METHODS

Two hundred sixty-nine patients were assessed on the Johnson Space Center physical activity scale. Patients were grouped according to whether they performed no physical activities (n=75), LPA (n=140), or MVPA (n=54). Primary measurements were total daily steps obtained from a step activity monitor worn for one week, peak walking time obtained from a treadmill test, the physical function score on the Medical Outcomes Study Short-Form 36 survey to assess HRQoL, and high-sensitivity C-reactive protein.

RESULTS

Total daily steps (mean±SD) was significantly different among groups, as both the LPA group (7878±2808 steps/day) and the MVPA group (8551±3365 steps/day) took more daily steps (p<0.01) than the sedentary group (3323±986 steps/day). Treadmill peak walking time was significantly different among groups, as both the LPA group (433±296 sec) and the MVPA group (548±300 sec) had greater peak walking time (p<0.01) than the sedentary group (302±210 sec). Physical function score was significantly different among groups, as both the LPA group (44±20%) and the MVPA group (58±19%) had higher scores (p<0.01) than the sedentary group (36±20%). Exercise time to the minimum calf muscle StO₂ was significantly different among groups, as both the LPA group (215±238 sec) and the MVPA group (377±351 sec) had greater values (p<0.05 and p<0.01, respectively) than the sedentary group (147±172 sec). Finally, high-sensitivity C-reactive protein was significantly different among groups, as both the LPA group (4.8±5.5 mg/L) and the MVPA group (3.5±3.6 mg/L) had lower values (p<0.01) than the sedentary group (8.6±8.4 mg/L).

CONCLUSIONS

Patients with claudication who reported performing LPA had greater amounts of objectively-determined physical activity levels and better physical function, HRQoL, and vascular measures than those who reported being physically sedentary. Furthermore, these favorable results associated with LPA were even more pronounced in patients who performed MVPA than in patients who were sedentary. The clinical significance is that engaging in any physical activity, even at relatively light intensity, is associated with favorable health and vascular measures in patients with claudication.

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.

Cognitive decrement in older adults with symptomatic peripheral artery disease

Peripheral artery disease (PAD) is highly prevalent, affecting up to 20% of people over 70 years of age. To test the hypothesis that PAD promotes the pathogenesis of vascular cognitive impairment (VCI), we compared cognitive function in older adults with symptomatic PAD and in participants without PAD who had a burden of comorbid conditions. Furthermore, we compared the cognitive function of these groups after adjusting for demographic and clinical characteristics, comorbid conditions, and cardiovascular risk factors. Participants with PAD (age: 69 ± 8 years; n = 58) and those without PAD (age: 62 ± 8 years; n = 30) were assessed on a battery of eight neuropsychological tests. The tests assessed attention and working memory, verbal memory, non-verbal memory, perceptuo-motor speed, and executive function. Participants were further characterized on demographic and clinical characteristics, comorbid conditions, cardiovascular risk factors, and ankle-brachial index. The PAD group had significantly lower neuropsychological scores than the non-PAD control group on all eight tests (P < .01). After adjusting for covariates, significantly worse scores in the PAD group persisted for verbal memory, measured by tests on logical memory-immediate recall (P = .022), and logical memory-delayed recall (P < .001), and for attention and working memory, measured by tests on digits forward (P < .001), and digits backward (P = .003). Participants with symptomatic PAD have substantially lower levels of performance on tests of attention, working memory, and verbal memory than participants without PAD independent of demographic characteristics and comorbid health burdens. These findings provide additional evidence in support of the concept that generalized accelerated vascular aging manifesting as symptomatic PAD in the peripheral circulation also affects the brain promoting the pathogenesis of VCI. These cognitive difficulties may also negatively impact symptomatic patient's ability to understand and adhere to behavioral and medical therapies, creating a vicious cycle. We speculate that more intensive follow-up may be needed to promote adherence to therapies and monitor cognitive decline that may affect care.

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.

The Use of Near Infrared Spectroscopy to Evaluate the Effect of Exercise on Peripheral Muscle Oxygenation in Patients with Lower Extremity Artery Disease: A Systematic Review

OBJECTIVE

Near infrared spectroscopy (NIRS) has been suggested as a new diagnostic tool in patients with lower extremity artery disease (LEAD). The aim of this systematic review was to summarise the impact of exercise therapy on lower limb muscle oxygenation, evaluated by NIRS, in patients with LEAD, and to give an overview on NIRS instruments and methodology.

DATA SOURCES

MEDLINE and Embase.

REVIEW METHODS

A systematic search was conducted in MEDLINE and Embase, from the earliest date available until 16 March 2020, to identify peer reviewed studies involving the use of NIRS in the evaluation of exercise training on muscle oxygenation in patients with LEAD. Primary outcomes were NIRS derived variables during treadmill exercise. Effect sizes were calculated as standardised mean differences. Assessment of methodological quality was done using a combined checklist from the Cochrane bias and the quality assessment tool for before and after studies without a control group.

RESULTS

Eleven original trials were included involving 16 exercise groups and four control groups. Tissue saturation index (TSI) at rest remained unchanged following the exercise interventions. Exercise training increased time to minimum TSI during exercise (range effect sizes: +0.172 to +0.927). In addition, exercise training led to a faster recovery to half and full TSI rest values in most intervention groups (range effect sizes -0.046 to -0.558 and -0.269 to -0.665, respectively). Finally, NIRS data reproducibility and analytic methods were under reported in the included studies.

CONCLUSION

The available data suggest that exercise training improves de-oxygenation and re-oxygenation patterns, as measured with NIRS, in patients with LEAD. Whereas NIRS is a promising tool in the evaluation of LEAD, the low number of randomised controlled trials, as well as large heterogeneity in NIRS assessment methods, outcome measures, and instrumentation, warrants more research to better understand the role of muscle oxygenation associated with exercise induced improvements in walking capacity.

Pathophysiology of Peripheral Arterial Disease (PAD): A Review on Oxidative Disorders

Peripheral arterial disease (PAD) is an atherosclerotic disease that affects a wide range of the world’s population, reaching up to 200 million individuals worldwide. PAD particularly affects elderly individuals (>65 years old). PAD is often underdiagnosed or underestimated, although specificity in diagnosis is shown by an ankle/brachial approach, and the high cardiovascular event risk that affected the PAD patients. A number of pathophysiologic pathways operate in chronic arterial ischemia of lower limbs, giving the possibility to improve therapeutic strategies and the outcome of patients. This review aims to provide a well detailed description of such fundamental issues as physical exercise, biochemistry of physical exercise, skeletal muscle in PAD, heme oxygenase 1 (HO-1) in PAD, and antioxidants in PAD. These issues are closely related to the oxidative stress in PAD. We want to draw attention to the pathophysiologic pathways that are considered to be beneficial in order to achieve more effective options to treat PAD patients.

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.

Bicycle exercise training improves ambulation in patients with peripheral artery disease

OBJECTIVE

Exercise training has multiple beneficial effects in patients with arteriosclerotic diseases; however, the exact underlying mechanisms of the effects are not completely understood. This study aimed to evaluate the effectiveness of a supervised exercise program in improving gait parameters, including the variability and walking performance of lower limb movements, in patients with peripheral artery disease (PAD) and intermittent claudication (IC).

METHODS

Sixteen patients with a history of PAD and IC were recruited for this study, and they completed a 3-month supervised bicycle exercise program. The ankle-brachial index and responses to quality of life (QOL) questionnaires were evaluated. Near-infrared spectroscopy was also performed to determine the hemoglobin oxygen saturation in the calf. Patients' kinematics and dynamics, including joint range of motion and muscle tension, were evaluated using an optical motion capture system. Computed tomography images of each muscle were assessed by manual outlining. Data were collected before and after the supervised bicycle exercise program, and differences were analyzed.

RESULTS

Significant differences were not found in step length, ankle-brachial index, and hemoglobin oxygen saturation before and after the supervised bicycle exercise program; however, IC distance (P = .034), maximum walking distance (P = .006), and all QOL questionnaire scores (P < .001) showed significant improvement. Hip range of motion (P = .035), maximum hip joint torque (right, P = .031; left, P = .044), maximum tension of the gluteus maximus muscle (right, P = .044; left, P = .042), and maximum hip joint work (right, P = .048; left, P = .043) also significantly decreased bilaterally. Computed tomography images showed a significant increase in the cross-sectional area of the abdominal, trunk, and thigh muscles but not in that of the lower leg muscles after the supervised exercise program intervention.

CONCLUSIONS

In this study, bicycle exercise training improved the QOL and walking distance and decreased hip movement. The results showed that bicycling might be as useful as walking 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.

Changes in vascular and inflammatory biomarkers after exercise rehabilitation in patients with symptomatic peripheral artery disease

OBJECTIVE

Home-based exercise is an alternative exercise mode to a structured supervised program to improve symptoms in patients with peripheral artery disease (PAD), but little is known about whether the slow-paced and less intense home program also elicits changes in vascular and inflammatory biomarkers. In an exploratory analysis from a randomized controlled trial, we compared changes in vascular and inflammatory biomarkers in patients with symptomatic PAD (typical and atypical of claudication) after home-based exercise and supervised exercise programs and in an attention-control group.

METHODS

A total of 114 patients were randomized into one of the three groups (n = 38 per group). Two groups performed exercise interventions, consisting of home-based and supervised programs of intermittent walking to mild to moderate claudication pain for 12 weeks; a third group performed light resistance training as a nonwalking attention-control group. Before and after intervention, patients were characterized on treadmill performance and endothelial effects of circulating factors present in sera by a cell culture-based bioassay on primary human arterial endothelial cells, and they were further evaluated on circulating vascular and inflammatory biomarkers.

RESULTS

Treadmill peak walking time increased (P = .008) in the two exercise groups but not in the control group (P > .05). Cultured endothelial cell apoptosis decreased after home-based exercise (P < .001) and supervised exercise (P = .007), and the change in the exercise groups combined was different from that in the control group (P = .005). For circulating biomarkers, increases were found in hydroxyl radical antioxidant capacity (P = .003) and vascular endothelial growth factor A (P = .037), and decreases were observed in E-selectin (P = .007) and blood glucose concentration (P = .012) after home-based exercise only. The changes in hydroxyl radical antioxidant capacity (P = .005), vascular endothelial growth factor A (P = .008), and E-selectin (P = .034) in the exercise groups combined were different from those in the control group.

CONCLUSIONS

This exploratory analysis found that both home-based and supervised exercise programs are efficacious to decrease cultured endothelial cell apoptosis in patients with symptomatic PAD. Furthermore, a monitored home-based exercise program elicits additional vascular benefits by improving circulating markers of endogenous antioxidant capacity, angiogenesis, endothelium-derived inflammation, and blood glucose concentration in patients with symptomatic PAD. The novel clinical significance is that important trends were found in this exploratory analysis that a contemporary home-based exercise program and a traditional supervised exercise program may favorably improve vascular and inflammatory biomarkers in addition to the well-described ambulatory improvements in symptomatic patients with PAD.

Greater Exercise Pressor Response Is Associated With Impaired Claudication Outcomes in Symptomatic Peripheral Artery Disease

We determined whether a greater exercise pressor response during a constant-load treadmill test was associated with lower peak walking time (PWT) and claudication onset time (COT) measured during a graded maximal treadmill test in 304 patients with symptomatic peripheral artery disease (PAD). The exercise pressor response was assessed by measuring heart rate and blood pressure (BP) at rest and during a constant-load treadmill test (speed = 2 mph, grade = 0%). After only 2 minutes of walking, mean heart rate increased by 26 beats/min from rest and mean systolic BP increased by 16 mm Hg. In adjusted analyses, increases in systolic BP (P = .021), heart rate (P = .002), mean arterial pressure (P = .034), and rate-pressure product (P < .001) from rest to 2 minutes of constant-load exercise were negatively associated with COT. Similarly, increases in heart rate (P = .012) and rate-pressure product (P = .018) from rest to 2 minutes of constant-load exercise were negatively associated with PWT. A greater exercise pressor response observed after only 2 minutes of walking at no incline was independently associated with impaired claudication outcomes in patients with symptomatic PAD. The implication is that the exercise pressor response is an important and easily obtained clinical measurement that partially explains differences in PWT and COT.

Characterising skeletal muscle haemoglobin saturation during exercise using near-infrared spectroscopy in chronic kidney disease

Background

Chronic kidney disease (CKD) patients have reduced exercise capacity. Possible contributing factors may include impaired muscle O₂ utilisation through reduced mitochondria number and/or function slowing the restoration of muscle ATP concentrations via oxidative phosphorylation. Using near-infrared spectroscopy (NIRS), we explored changes in skeletal muscle haemoglobin/myoglobin O₂ saturation (SMO₂%) during exercise.

Methods

24 CKD patients [58.3 (± 16.5) years, eGFR 56.4 (± 22.3) ml/min/1.73 m²] completed the incremental shuttle walk test (ISWT) as a marker of exercise capacity. Using NIRS, SMO₂% was measured continuously before, during, and after (recovery) exercise. Exploratory differences were investigated between exercise capacity tertiles in CKD, and compared with six healthy controls.

Results

We identified two discrete phases; a decline in SMO₂% during incremental exercise, followed by rapid increase upon cessation (recovery). Compared to patients with low exercise capacity [distance walked during ISWT, 269.0 (± 35.9) m], patients with a higher exercise capacity [727.1 (± 38.1) m] took 45% longer to reach their minimum SMO₂% (P = .038) and recovered (half-time recovery) 79% faster (P = .046). Compared to controls, CKD patients took significantly 56% longer to recover (i.e., restore SMO₂% to baseline, full recovery) (P = .014).

Conclusions

Using NIRS, we have determined for the first time in CKD, that favourable SMO₂% kinetics (slower deoxygenation rate, quicker recovery) are associated with greater exercise capacity. These dysfunctional kinetics may indicate reduced mitochondria capacity to perform oxidative phosphorylation—a process essential for carrying out even simple activities of daily living. Accordingly, NIRS may provide a simple, low cost, and non-invasive means to evaluate muscle O₂ kinetics in CKD.

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.

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.

Experimental intermittent ischemia augments exercise-induced inflammatory cytokine production

Acute exercise-induced inflammation is implicated in mediating the beneficial adaptations to regular exercise. Evidence suggests that reduced oxygen and/or blood flow to contracting muscle alters cytokine appearance. However, the acute inflammatory responses to hypoxic/ischemic exercise have been documented with inconsistent results and may not accurately reflect the ischemia produced during exercise in patients with ischemic cardiovascular diseases. Therefore, we determined the extent to which local inflammation is involved in the response to ischemic exercise. Fourteen healthy males performed unilateral isometric forearm contractions for 30 min with and without experimental ischemia. Blood was drawn at baseline, 5 and 10 min into exercise, at the end of exercise, and 30, 60, and 120 min after exercise. Oxygen saturation levels, as measured by near-infrared spectroscopy, were reduced by 10% and 41% during nonischemic and ischemic exercise, respectively. Nonischemic exercise did not affect cytokine values. Ischemia enhanced concentrations of basic fibroblast growth factor, interleukin (IL)-6, IL-10, tumor necrosis factor-alpha, and vascular endothelial growth factor during exercise, but IL-8 was not influenced by ischemic exercise. In conclusion, the present study demonstrates that ischemic, small-muscle endurance exercise elicits local inflammatory cytokine production compared with nonischemic exercise.

NEW & NOTEWORTHY We demonstrate that ischemic, small-muscle endurance exercise elicits local inflammatory cytokine production compared with nonischemic exercise. The present study advances our knowledge of the inflammatory response to exercise in a partial ischemic state, which may be relevant for understanding the therapeutic effects of exercise training for people with ischemic cardiovascular disease-associated comorbidities.

Physical activity, immune function and inflammation in kidney patients (the PINK study): a feasibility trial protocol

INTRODUCTION

Patients with chronic kidney disease (CKD) display increased infection-related mortality and elevated cardiovascular risk only partly attributed to traditional risk factors. Patients with CKD also exhibit a pro-inflammatory environment and impaired immune function. Aerobic exercise has the potential to positively impact these detriments, but is under-researched in this patient population. This feasibility study will investigate the effects of acute aerobic exercise on inflammation and immune function in patients with CKD to inform the design of larger studies intended to ultimately influence current exercise recommendations.

METHODS AND ANALYSIS

Patients with CKD, including renal transplant recipients, will visit the laboratory on two occasions, both preceded by appropriate exercise, alcohol and caffeine restrictions. On visit 1, baseline assessments will be completed, comprising anthropometrics, body composition, cardiovascular function and fatigue and leisure time exercise questionnaires. Participants will then undertake an incremental shuttle walk test to estimate predicted peak O2 consumption (VO2peak). On visit 2, participants will complete a 20 min shuttle walk at a constant speed to achieve 85% estimated VO2peak. Blood and saliva samples will be taken before, immediately after and 1 hour after this exercise bout. Muscle O2 saturation will be monitored throughout exercise and recovery. Age and sex-matched non-CKD 'healthy control' participants will complete an identical protocol. Blood and saliva samples will be analysed for markers of inflammation and immune function, using cytometric bead array and flow cytometry techniques. Appropriate statistical tests will be used to analyse the data.

ETHICS AND DISSEMINATION

A favourable opinion was granted by the East Midlands-Derby Research Ethics Committee on 18 September 2015 (ref 15/EM/0391), and the study was approved and sponsored by University Hospitals of Leicester Research and Innovation (ref 11444). The study was registered with ISRCTN (ref 38935454). The results will be presented at relevant conferences, and it is anticipated that the reports will be published in appropriate journals in 2018.

Association between daily walking and antioxidant capacity in patients with symptomatic peripheral artery disease

OBJECTIVE

The primary aim of the study was to assess whether both the amount and pace of daily walking were associated with circulating antioxidant capacity in symptomatic patients with peripheral artery disease (PAD).

METHODS

Community-based walking was measured in 244 men and women who were limited by symptomatic PAD during a 1-week period in which they wore an ankle-mounted step activity monitor. Patients were further characterized by circulating antioxidant capacity with the OxiSelect (Cell Biolabs Inc, San Diego, Calif) hydroxyl radical antioxidant capacity (HORAC) activity assay.

RESULTS

To assess the amount of walking, patients were grouped into low (≤2440 strides/d), middle (2441-3835 strides/d), and high (>3835 strides/d) stride tertiles. HORAC was higher in the middle (P = .03) and high (P = .01) stride tertiles than in the low tertile, but there was no difference between middle and high tertiles (P = .44). To assess the pace of walking, patients were grouped into slow (<25.0 strides/min), middle (25.0-31.6 strides/min), and fast (>31.6 strides/min) cadence tertiles. HORAC was higher in the high cadence tertile than in the low (P < .01) and middle (P < .01) tertiles, but there was no difference between low and middle tertiles (P = .48). Similar findings were obtained on group differences in HORAC after adjusting for age, sex, race, and ankle-brachial index for both the amount and pace of daily walking.

CONCLUSIONS

Walking >2440 strides each day and walking at a cadence faster than 31.6 strides/min for 30 minutes each day are both associated with greater circulating antioxidant capacity in symptomatic patients with PAD. The clinical significance is that a home-based walking program may be one approach to increase endogenous antioxidant capacity.

Effect of cognitive status on exercise performance and quality of life in patients with symptomatic peripheral artery disease

BACKGROUND

We determined whether scores on a cognitive screening measure were associated with the primary outcome measure of peak walking time (PWT) and with secondary outcome measures related to mobility, community-based ambulation, health-related quality of life (QoL), and vascular function in patients with claudication and peripheral artery disease (PAD).

METHODS

Gross cognitive status of 246 PAD patients was assessed with the Mini-Mental State Examination (MMSE) questionnaire. Patients were grouped according to whether they had a perfect MMSE score of 30 points (n = 123) or whether they missed one or more points (n = 123). Patients were characterized on numerous outcomes, including PWT during a treadmill test and QoL.

RESULTS

Compared with the group with the higher MMSE scores, there was a trend for lower PWT in the group with the lower MMSE scores (P = .06) after adjusting for age, sex, race, and education level (model 1), which became significant (380 ± 250 seconds vs 460 ± 270 seconds; P < .05) after adjusting for model 1 plus coronary artery disease, chronic obstructive pulmonary disease, and arthritis (model 2). Multiple domains of QoL were lower (P < .05) in the group with the lower MMSE scores after adjusting for model 1, but only mental health remained lower (75 ± 20% vs 80 ± 5%; P = .02) after further adjustment with model 2.

CONCLUSIONS

In symptomatic patients with PAD, lower cognitive screening scores were associated with greater ambulatory impairment than in patients with higher MMSE scores. Furthermore, worse cognitive status was associated with lower scores in multiple dimensions of health-related QoL, all of which except mental health were explained by the comorbid conditions of coronary artery disease, chronic obstructive pulmonary disease, and arthritis. The clinical significance is that there is a need for enhanced cognitive and mental health screening as potential indicators of poor outcome among symptomatic patients with PAD. Furthermore, patients identified as having worse cognitive status might be in greatest need of intervention to improve ambulation and QoL related to mental health.

Endothelial Cell Inflammation and Antioxidant Capacity are Associated With Exercise Performance and Microcirculation in Patients With Symptomatic Peripheral Artery Disease

We determined whether exercise performance and lower extremity microcirculation were associated with endothelial cell inflammation, oxidative stress, and apoptosis and with circulating biomarkers of inflammation and antioxidant capacity in 160 patients with symptomatic peripheral artery disease (PAD). In a multivariate regression model for peak walking time, significant independent variables included ankle-brachial index (P < .001), age (P = .017), hydroxyl radical antioxidant capacity (P = .008), and endothelial cell nuclear factor K-light-chain-enhancer of activated B cells (NF-κB) activity (P = .015). In multivariate analyses for time to minimum exercise calf muscle hemoglobin oxygen saturation (StO2), significant independent variables included endothelial cell NF-κB activity (P = .043) and calf muscle StO2 at rest (P = .007). Endothelial cell inflammation and circulating biomarkers of inflammation and antioxidant capacity were associated with exercise performance and microcirculation of the ischemic calf musculature during exercise. The clinical implication is that interventions designed to alleviate endothelial cell inflammation and circulating inflammatory biomarkers, such as antioxidant therapy, may improve exercise performance of symptomatic patients with PAD.

Step-monitored home exercise improves ambulation, vascular function, and inflammation in symptomatic patients with peripheral artery disease: a randomized controlled trial

Background

This prospective, randomized, controlled clinical trial compared changes in primary outcome measures of claudication onset time (COT) and peak walking time (PWT), and secondary outcomes of submaximal exercise performance, daily ambulatory activity, vascular function, inflammation, and calf muscle hemoglobin oxygen saturation (StO₂) in patients with symptomatic peripheral artery disease (PAD) following new exercise training using a step watch (NEXT Step) home‐exercise program, a supervised exercise program, and an attention‐control group.

Methods and Results

One hundred eighty patients were randomized. The NEXT Step program and the supervised exercise program consisted of intermittent walking to mild‐to‐moderate claudication pain for 12 weeks, whereas the controls performed light resistance training. Change scores for COT (P<0.001), PWT (P<0.001), 6‐minute walk distance (P=0.028), daily average cadence (P=0.011), time to minimum calf muscle StO₂ during exercise (P=0.025), large‐artery elasticity index (LAEI) (P=0.012), and high‐sensitivity C‐reactive protein (hsCRP) (P=0.041) were significantly different among the 3 groups. Both the NEXT Step home program and the supervised exercise program demonstrated a significant increase from baseline in COT, PWT, 6‐minute walk distance, daily average cadence, and time to minimum calf StO₂. Only the NEXT Step home group had improvements from baseline in LAEI, and hsCRP (P<0.05).

Conclusions

NEXT Step home exercise utilizing minimal staff supervision has low attrition, high adherence, and is efficacious in improving COT and PWT, as well as secondary outcomes of submaximal exercise performance, daily ambulatory activity, vascular function, inflammation, and calf muscle StO₂ in symptomatic patients with PAD.

Clinical Trial Registration

URL: ClinicalTrials.gov. Unique Identifier: NCT00618670.

Gender and racial differences in endothelial oxidative stress and inflammation in patients with symptomatic peripheral artery disease

BACKGROUND

We compared (1) cellular reactive oxygen species (ROS) production, inflammation, and apoptosis of cultured endothelial cells treated with sera and (2) circulating inflammatory measures, antioxidant capacity, vascular biomarkers, and calf muscle hemoglobin oxygen saturation (StO2) in men and women with peripheral artery disease (PAD). A secondary aim was to compare exercise performance and daily ambulatory activity between men and women. We hypothesized that women would have more impaired endothelial cellular ROS, inflammation, and apoptosis than men as well as worse systemic inflammation, antioxidant capacity, vascular biomarkers, calf muscle StO2, exercise performance, and daily ambulatory activity.

METHODS

The 148 symptomatic men and women with PAD were characterized on the endothelial effects of circulating factors present in the sera by a cell culture-based bioassay on primary human arterial endothelial cells. Patients were further evaluated by circulating inflammatory and vascular biomarkers, physical examination and medical history, exercise performance, and calf muscle StO2 during exercise, and ambulatory activity was monitored during 1 week.

RESULTS

Cellular ROS production was higher in African American women than in men (P = .021), but there was no gender difference in white individuals (P = .537). Men and women were not significantly different on endothelial cell apoptosis (P = .833) and nuclear factor κB activity (P = .465). For circulating factors, additional gender differences were found when comparisons were made within each race. In African Americans, women had higher intercellular adhesion molecule 1 (P = .022) and leptin (P < .001); whereas in white individuals, women had higher matrix metallopeptidase 9 (P = .047), higher vascular cell adhesion molecule 1 (P = .047), and lower hepatocyte growth factor (P = .046). Overall, women had higher apolipoprotein CIII (P = .035), lower pain-free distance (P = .048) and total distance (P < .001) during the 6-minute walk test, shorter time for calf muscle StO2 to reach the minimum value during exercise (P = .027), and slower average cadence (P = .004) during daily ambulation.

CONCLUSIONS

African American women with symptomatic PAD have a heightened oxidative status, likely resulting in increased endothelial oxidative stress, compared with men. Furthermore, women exhibit a more pronounced proinflammatory profile of circulating biomarkers as well as more limited peripheral microcirculation, exercise performance, and ambulatory activity than men do. The clinical significance is that women with symptomatic PAD are in greater need than men of clinical intervention to improve oxidative stress, inflammation, and microcirculation, which may in turn have a favorable impact on their lower exercise performance and daily activity.

The effects of smoking status on walking ability and health-related quality of life in patients with peripheral arterial disease

BACKGROUND

Smoking is a leading risk factor for peripheral arterial disease (PAD), yet little is known about the interrelationships among smoking status, walking endurance, calf muscle tissue oxygenation, and quality of life in patients with PAD.

OBJECTIVE

The aim of this study was to explore the differences in factors associated with walking endurance including walk distance, perceived walking ability, measures of skeletal muscle tissue oxygenation (StO2), claudication pain, peak oxygen consumption per unit time, and quality of life in smokers versus nonsmokers.

METHODS

A total of 105 patients with PAD performed progressive, symptom-limited treadmill test. Ankle-brachial index was measured at baseline. Calf muscle tissue oxygenation measures were obtained during testing. The RAND Short Form-36 and Walking Impairment Questionnaire were used to measure health-related quality of life (HR-QoL).

RESULTS

In the total sample (36 current smokers, 69 nonsmokers), smokers had steeper declines in StO2 from baseline to 2 minutes (42.3% vs 33%, P = .05) and shorter distance walked to onset of claudication pain (142.6 vs 247.7 m) than did nonsmokers (P < .0125), despite having no differences in ankle-brachial index, peak oxygen consumption per unit time, or any momentary measure of StO2 during walking. Smokers reported significantly lower HR-QoL on the Short Form-36 in several domains but no differences in the Walking Impairment Questionnaire measures. The smokers were younger than the nonsmokers; however, when age was entered as a covariate in the analyses, the results remained unchanged.

CONCLUSIONS

These findings suggest that smokers have lower HR-QoL than do nonsmokers with PAD and that smoking confers risks for disrupted tissue oxygenation above those seen in patients who do not smoke.

Diffuse optical characterization of an exercising patient group with peripheral artery disease

Peripheral artery disease (PAD) is a common condition with high morbidity. While measurement of tissue oxygen saturation (S(t)O(2)) has been demonstrated, this is the first study to assess both S(t)O(2) and relative blood flow (rBF) in the extremities of PAD patients. Diffuse optics is employed to measure hemodynamic response to treadmill and pedal exercises in 31 healthy controls and 26 patients. For S(t)O(2), mild and moderate/severe PAD groups show pronounced differences compared with controls. Pre-exercise mean S(t)O(2) is lower in PAD groups by 9.3% to 10.6% compared with means of 63.5% to 66.2% in controls. For pedal, relative rate of return of S(t)O(2) to baseline is more rapid in controls (p < 0.05). Patterns of rBF also differ among groups. After both exercises, rBF tend to occur at depressed levels among severe PAD patients compared with healthy (p < 0.05); post-treadmill, rBF tend to occur at elevated levels among healthy compared with severe PAD patients (p < 0.05). Additionally, relative rate of return to baseline S(t)O(2) is more rapid among subjects with reduced levels of depression in rBF (p = 0.041), even after adjustment for ankle brachial index. This suggests a physiologic connection between rBF and oxygenation that can be measured using diffuse optics, and potentially employed as an evaluative tool in further studies.

Comparison of muscle and skin perfusion over the ischial tuberosities in response to wheelchair tilt-in-space and recline angles in people with spinal cord injury

OBJECTIVE

To compare the efficacy of wheelchair tilt-in-space and recline on enhancing muscle and skin perfusion over the ischial tuberosities in people with spinal cord injury (SCI).

DESIGN

Repeated-measures and before-after trial design.

SETTING

University research laboratory.

PARTICIPANTS

Power wheelchair users with SCI (N=20).

INTERVENTIONS

Six combinations of wheelchair tilt-in-space and recline angles were presented to participants in a random order. The testing protocol consisted of a baseline 5 minutes sitting with no tilt/recline and 5 minutes positioned in a tilted and reclined position at each of 6 conditions, including: (1) 15° tilt-in-space and 100° recline, (2) 25° tilt-in-space and 100° recline, (3) 35° tilt-in-space and 100° recline, (4) 15° tilt-in-space and 120° recline, (5) 25° tilt-in-space and 120° recline, and (6) 35° tilt-in-space and 120° recline.

MAIN OUTCOME MEASURES

Muscle and skin perfusion were assessed by near-infrared spectroscopy and laser Doppler flowmetry, respectively.

RESULTS

Muscle perfusion was significantly increased at 25° and 35° tilt-in-space when combined with 120° recline, and skin perfusion was significantly increased at 3 tilt-in-space angles (15°, 25°, 35°) when combined with 120° recline and at 35° tilt-in-space when combined with 100° recline (P<.05). Even in the positions of increased muscle perfusion and skin perfusion (25° and 35° of tilt-in-space combined with 120° of recline), the amount of muscle perfusion change was significantly lower than the amount of skin perfusion change (P<.05).

CONCLUSIONS

Our results indicate that a larger angle of tilt-in-space and recline is needed to improve muscle perfusion compared with skin perfusion. A position of 25° tilt-in-space combined with 120° recline is effective in enhancing muscle and skin perfusion of weight-bearing soft tissues at the ischial tuberosities.

Comparison of walking with poles and traditional walking for peripheral arterial disease rehabilitation

PURPOSE

The purpose of this study was to compare the effects of a 24-week walking with poles rehabilitation program with a traditional 24-week walking program on physical function in patients with peripheral arterial disease (PAD).

METHODS

Patients with PAD (n = 103, age = 69.7 ± 8.9 years, ankle-brachial index < 0.90 or evidence of calcified vessels) were randomized into a rehabilitation program of traditional walking (n = 52) or walking with poles (n = 51). Patients exercised 3 times per week for 24 weeks. Exercise endurance was measured by time walked on a constant work rate treadmill test at 6, 12, and 24 weeks. Perceived physical function was measured by the Medical Outcomes Study Short Form-36 and Walking Impairment Questionnaire. Tissue oxygenation was measured using near-infrared spectroscopy.

RESULTS

Patients assigned to the traditional walking group walked longer at 24 weeks than those assigned to the pole walking group (21.10 ± 17.07 minutes and 15.02 ± 12.32 minutes, respectively, P = .037). There were no differences between the groups in tissue oxygenation. However, there was a significant lengthening of time for which it took to reach minimum tissue oxygenation values (P < .001) within the groups on the constant work rate test. There were no differences between the groups in perceived physical function as measured by the Physical Function subscale on the Medical Outcomes Study Short Form-36 or perceived walking distance as measured by the Walking Distance subscale on the Walking Impairment Scale.

CONCLUSIONS

Traditional walking was superior to walking with poles in increasing walking endurance on a constant work rate treadmill test for patients with PAD.

Exercise training and peripheral arterial disease

Peripheral arterial disease (PAD) is a common vascular disease that reduces blood flow capacity to the legs of patients. PAD leads to exercise intolerance that can progress in severity to greatly limit mobility, and in advanced cases leads to frank ischemia with pain at rest. It is estimated that 12 to 15 million people in the United States are diagnosed with PAD, with a much larger population that is undiagnosed. The presence of PAD predicts a 50% to 1500% increase in morbidity and mortality, depending on severity. Treatment of patients with PAD is limited to modification of cardiovascular disease risk factors, pharmacological intervention, surgery, and exercise therapy. Extended exercise programs that involve walking approximately five times per week, at a significant intensity that requires frequent rest periods, are most significant. Preclinical studies and virtually all clinical trials demonstrate the benefits of exercise therapy, including improved walking tolerance, modified inflammatory/hemostatic markers, enhanced vasoresponsiveness, adaptations within the limb (angiogenesis, arteriogenesis, and mitochondrial synthesis) that enhance oxygen delivery and metabolic responses, potentially delayed progression of the disease, enhanced quality of life indices, and extended longevity. A synthesis is provided as to how these adaptations can develop in the context of our current state of knowledge and events known to be orchestrated by exercise. The benefits are so compelling that exercise prescription should be an essential option presented to patients with PAD in the absence of contraindications. Obviously, selecting for a lifestyle pattern that includes enhanced physical activity prior to the advance of PAD limitations is the most desirable and beneficial.

The Effects of Walking or Walking-with-Poles Training on Tissue Oxygenation in Patients with Peripheral Arterial Disease

This randomized trial proposed to determine if there were differences in calf muscle StO₂ parameters in patients before and after 12 weeks of a traditional walking or walking-with-poles exercise program. Data were collected on 85 patients who were randomized to a traditional walking program (n = 40) or walking-with-poles program (n = 45) of exercise training. Patients walked for 3 times weekly for 12 weeks. Seventy-one patients completed both the baseline and the 12-week follow-up progressive treadmill tests (n = 36 traditional walking and n = 35 walking-with-poles). Using the near-infrared spectroscopy measures, StO₂ was measured prior to, during, and after exercise. At baseline, calf muscle oxygenation decreased from 56 ± 17% prior to the treadmill test to 16 ± 18% at peak exercise. The time elapsed prior to reaching nadir StO₂ values increased more in the traditional walking group when compared to the walking-with-poles group. Likewise, absolute walking time increased more in the traditional walking group than in the walking-with-poles group. Tissue oxygenation decline during treadmill testing was less for patients assigned to a 12-week traditional walking program when compared to those assigned to a 12-week walking-with-poles program. In conclusion, the 12-week traditional walking program was superior to walking-with-poles in improving tissue deoxygenation in patients with PAD.

Clinical significance of ankle systolic blood pressure following exercise in assessing calf muscle tissue ischemia in peripheral artery disease

Our primary objective assessed whether a decline in ankle systolic blood pressure (SBP) to less than 50 mm Hg after treadmill exercise is associated with lower extremity ischemia, as measured by calf muscle hemoglobin oxygen saturation (StO(2)). Eighty-four patients with peripheral artery disease (PAD) completed a treadmill test. Ankle SBP <50 mm Hg following exercise was observed in only 49% (group 1), whereas 51% had ankle SBP ≥50 mm Hg (group 2). No group differences were observed for the decline in calf muscle StO(2) to a minimum value (group 1: 18 ± 21%, group 2: 20 ± 20%; P = .60) and for the time to reach minimum StO(2) (group 1: 224 ± 251 seconds, group 2: 284 ± 283 seconds; P = .30). Requirement of ankle SBP to decrease below 50 mm Hg after exercise has little clinical significance for assessing ischemia in calf muscle of patients with PAD limited by intermittent claudication.

Cardiovascular responses to walking in patients with peripheral artery disease

PURPOSES

The study's purposes were to assess the cardiovascular responses during constant-load walking and to identify predictors of this response in peripheral artery disease (PAD) patients.

METHODS

Seventy-nine patients with PAD performed a constant-load treadmill test (2 mph, 0% grade). During the test, systolic blood pressure (BP), diastolic BP, and HR were obtained at the fourth minute to the last minute of exercise. Patients were also characterized by demographic measures, cardiovascular risk factors, baseline exercise performance, and vascular measures.

RESULTS

During constant-load walking, there was a significant increase (P < 0.01) in systolic BP (+12 ± 10 mm Hg), diastolic BP (+6 ± 9 mm Hg), and HR (+5 ± 5 bpm). The HR responses were negatively correlated with the ischemic window (r = -0.23, P < 0.05), expressed as an area under the curve of the resting ankle systolic BP and its recovery from a maximal graded treadmill test, and positively correlated with the HR during the first minute of recovery from the maximal graded treadmill test (r = 0.27, P < 0.05). The increase in cardiovascular variables during constant-load walking was greater in subjects with a higher body mass index and in men (P < 0.05).

CONCLUSIONS

Patients with PAD had an increased cardiovascular response during constant-load walking, and these responses were greater in obese patients and in men. The clinical implication is that PAD patients engaged in walking training programs, particularly men and those with obesity, require frequent assessment of cardiovascular parameters to avoid exaggerated increases in BP and HR during constant-load walking.

Calf muscle hemoglobin oxygen saturation in patients with peripheral artery disease who have different types of exertional leg pain

BACKGROUND

This study compared calf muscle hemoglobin oxygen saturation (Sto(2)) and exercise performance during standardized treadmill exercise in patients with peripheral artery disease (PAD) who describe different types of exertional leg pain and compared secondary outcomes consisting of daily ambulatory activity and exercise performance during a 6-minute walk test (6MWT).

METHODS

Leg pain symptoms were evaluated in 114 patients with PAD using the San Diego Claudication Questionnaire, by which atypical exertional leg pain was defined in 31, claudication in 37, and leg pain on exertion and rest in 46. Patients were evaluated on a standardized, graded treadmill test during which calf muscle Sto(2) was continuously monitored. The 6MWT distance, Walking Impairment Questionnaire (WIQ), and ambulatory activity were monitored during 1 week.

RESULTS

All patients experienced symptoms during the treadmill test consistent with claudication. The groups were not significantly different on the primary outcomes of time to reach the minimum calf muscle Sto(2) (P = .350) or peak walking time (P = .238) during treadmill exercise. Patients with atypical leg pain had the highest daily ambulatory activity for total strides per day (P = .032), average daily cadence (P = .010), maximum cadences for durations between 5 minutes (P = .035) and 60 minutes (P = .029), speed score on the WIQ (P = .006), and lowest rating of perceived exertion at the end of the 6MWT (P = .017).

CONCLUSIONS

PAD patients with atypical leg pain have vascular-mediated limitations in exercise performance during standardized treadmill testing similar to patients with claudication and patients with leg pain on exertion and rest but have higher levels of daily ambulatory activity in the community setting and higher perceived ambulatory function.

Gender differences in daily ambulatory activity patterns in patients with intermittent claudication

OBJECTIVES

To compare the pattern of daily ambulatory activity in men and women with intermittent claudication, and to determine whether calf muscle hemoglobin oxygen saturation (StO2) is associated with daily ambulatory activity.

METHODS

Forty men and 41 women with peripheral arterial disease limited by intermittent claudication were assessed on their community-based ambulatory activity patterns for 1 week with an ankle-mounted step activity monitor and on calf muscle StO2 during a treadmill test.

RESULTS

Women had lower adjusted daily maximal cadence (mean±SE) for 5 continuous minutes of ambulation (26.2±1.2 strides/min vs 31.0±1.2 strides/min; P=.009), for 1 minute of ambulation (43.1±0.9 strides/min vs 47.2±0.9 strides/min; P=.004), and for intermittent ambulation determined by the peak activity index (26.3±1.2 strides/min vs 31.0±1.2 strides/min; P=.009). Women also had lower adjusted time to minimum calf muscle StO2 during exercise (P=.048), which was positively associated with maximal cadence for 5 continuous minutes (r=0.51; P<.01), maximal cadence for 1 minute (r=0.42; P<.05), and peak activity index (r=0.44; P<.05). These associations were not significant in men.

CONCLUSION

Women with intermittent claudication ambulate slower in the community setting than men, particularly for short continuous durations of up to 5 minutes and during intermittent ambulation at peak cadences. Furthermore, the daily ambulatory cadences of women are correlated with their calf muscle StO2 during exercise, as women who walk slower in the community setting reach their minimum calf muscle StO2 sooner than those who walk at faster paces. Women with intermittent claudication should be encouraged to not only walk more on a daily basis, but to do so at a pace that is faster than their preferred speed.

Reduced high-density lipoprotein level is linked to worse ankle brachial index and peak oxygen uptake in postmenopausal women with peripheral arterial disease

Women with peripheral arterial disease (PAD) have more limited physical function than men but the mechanisms involved are not clear. We determined whether alterations in lipid components, such as decreased high-density lipoprotein cholesterol (HDL-C), are associated with worsening intermittent claudication (IC) in postmenopausal women with PAD. Our cross-sectional cohort study included 69 postmenopausal women with IC (Fontaine stage II). A treadmill test was used to measure initial claudication distance (ICD), absolute claudication distance (ACD), peak oxygen uptake, and ankle systolic blood pressure. High-density lipoprotein cholesterol correlated with ankle brachial index ([ABI]; R = .29, P = .019). No other lipid profile components were associated with exercise performance and hemodynamic measures. Among women with HDL-C <50 mg/dL (n = 43), the median peak oxygen uptake level was significantly lower (P = .021) relative to women with normal HDL-C >50 mg/dL (n = 26). Lower HDL-C levels are associated with worse ABI and decreased peak oxygen uptake in postmenopausal women with PAD.

Limb-specific and cross-transfer effects of arm-crank exercise training in patients with symptomatic peripheral arterial disease

Arm cranking is a useful alternative exercise modality for improving walking performance in patients with intermittent claudication; however, the mechanisms of such an improvement are poorly understood. The main aim of the present study was to investigate the effects of arm-crank exercise training on lower-limb O2 delivery in patients with intermittent claudication. A total of 57 patients with intermittent claudication (age, 70±8 years; mean±S.D.) were randomized to an arm-crank exercise group or a non-exercise control group. The exercise group trained twice weekly for 12 weeks. At baseline and 12 weeks, patients completed incremental tests to maximum exercise tolerance on both an arm-crank ergometer and a treadmill. Respiratory variables were measured breath-by-breath to determine peak V̇O2 (O2 uptake) and ventilatory threshold. Near-IR spectroscopy was used in the treadmill test to determine changes in calf muscle StO2 (tissue O2 saturation). Patients also completed a square-wave treadmill-walking protocol to determine V̇O2 kinetics. A total of 51 patients completed the study. In the exercise group, higher maximum walking distances (from 496±250 to 661±324 m) and peak V̇O2 values (from 17.2±2.7 to 18.2±3.4 ml·kg−1 of body mass·min−1) were recorded in the incremental treadmill test (P<0.05). After training, there was also an increase in time to minimum StO2 (from 268±305 s to 410±366 s), a speeding of V̇O2 kinetics (from 44.7±10.4 to 41.3±14.4 s) and an increase in submaximal StO2 during treadmill walking (P<0.05). There were no significant changes in the control group. The results suggest that the improvement in walking performance after arm-crank exercise training in patients with intermittent claudication is attributable, at least in part, to improved lower-limb O2 delivery.

Sex differences in calf muscle hemoglobin oxygen saturation in patients with intermittent claudication

PURPOSES

We tested the hypotheses that women have greater impairment in calf muscle hemoglobin oxygen saturation (StO(2)) in response to exercise than men, and that the sex-related difference in calf muscle StO(2) would partially explain the shorter claudication distances of women.

METHODS

The study comprised 27 men and 24 women with peripheral arterial disease limited by intermittent claudication. Patients were characterized on calf muscle StO(2) before, during, and after a graded treadmill test, as well as on demographic and cardiovascular risk factors, ankle-brachial index (ABI), ischemic window, initial claudication distance (ICD), and absolute claudication distance (ACD).

RESULTS

Women had a 45% lower ACD than men (296 +/- 268 m vs 539 +/- 288 m; P = .001) during the treadmill test. Calf muscle StO(2) declined more rapidly during exercise in women than in men; the time to reach minimum StO(2) occurred 54% sooner in women (226 +/- 241 vs 491 +/- 426 seconds; P = .010). The recovery time for calf muscle StO(2) to reach the resting value after treadmill exercise was prolonged in women (383 +/- 365 vs 201 +/- 206 seconds; P = .036). Predictors of ACD included the time from start of exercise to minimum calf muscle StO(2), the average rate of decline in StO(2) from rest to minimum StO(2) value, the recovery half-time of StO(2), and ABI (R(2) = 0.70; P < .001). The ACD of women remained lower after adjusting for ABI (mean difference, 209 m; P = .003), but was no longer significantly lower (mean difference, 72 m; P = .132) after further adjustment for the StO(2) variables for the three calf muscles.

CONCLUSION

In patients limited by intermittent claudication, women have lower ACD and greater impairment in calf muscle StO(2) during and after exercise than men, the exercise-mediated changes in calf muscle StO(2) are predictive of ACD, and women have similar ACD as men after adjusting for calf StO(2) and ABI measures.

Training-induced vascular adaptations to ischemic muscle

Peripheral arterial insufficiency is a progressive degenerative disease associated with an increased morbidity and mortality. It decreases exercise tolerance and often presents with symptoms of intermittent claudication. Enhanced physical activity is one of the most effective means of improving the life of affected patients. While this occurs for a variety of reasons, vascular remodeling can be an important means for improved oxygen exchange and blood flow delivery. Relevant exercise-induced signals stimulate angiogenesis, within the active muscle (e.g. hypoxia), and arteriogenesis (enlargement of pre-existing vessels via increased shear stress) to increase oxygen exchange and blood flow capacity, respectively. Evidence from pre-clinical studies shows that the increase in collateral blood flow observed with exercise progresses over time of training, is accompanied by significant enlargement of isolated collateral vessels, and enhances the responses observed with angiogenic growth factors (e.g. VEGF, FGF-2). Thus, enhanced physical activity can be an effective means of enlarging the structure and function of the collateral circuit. Interestingly, disrupting normal NO production (via L-NAME) eliminates this increase in collateral blood flow induced by training, but does not disturb the increase in muscle capillarity within the active muscle. Similarly, inhibiting VEGF receptor kinase activity eliminates the increase in collateral-dependent blood flow, and lessens, but does not eliminate, angiogenesis within the calf muscle. These findings illustrate distinctions between the processes influencing angiogenesis and arteriogenesis. Further, sympathetic modulation of the collateral circuit does not eliminate the increase in collateral circuit conductance induced by exercise training. These findings indicate that structural enlargement of the collateral vessels is essential to realize the increase in collateral-dependent blood flow capacity caused by exercise training. This raises the potential that meaningful vascular remodeling can occur in patients with intermittent claudication who actively participate in exercise training.