Practical equations to predict claudication pain distances from a graded treadmill test

Predictors of walking capacity in patients with peripheral arterial disease

BACKGROUND

Walking capacity is severely impaired in patients with peripheral arterial disease (PAD). Given the prognostic importance of walking capacity, the level of evidence on possible predictors of walking capacity in patients with PAD is insufficient.

AIMS

To investigate the predictors of walking capacity in patients with PAD.

METHODS

A total of 51 patients with PAD were included in this cross-sectional study. Walking capacity was determined with 6‑minute walk test (6MWT) and walking impairment questionnaire (WIQ). Functional mobility was assessed with repeated sit-to-stand test (RSS) and timed up and go test (TUG). Hand-held dynamometer was used to measurement lower extremity muscle strength. Balance was assessed with Biodex Balance System-limit of stability (BBS-LOS). Fatigue was evaluated with fatigue impact scale (FIS).

RESULTS

There was a strong correlation between 6MWT walking distance and WIQ, two methods of assessing walking capacity (r = 0.835 p < 0.001). The 6MWT was correlated with RSS, TUG, lower extremity muscle strength, BBS-LOS and FIS. The WIQ was correlated with RSS, TUG, BBS-LOS and FIS. The RSS and FIS were independent determinants of the 6MWT and WIQ, accounting for 68% and 57% of the variance, respectively.

CONCLUSION

This study demonstrated that functional mobility and fatigue were independent predictors of walking capacity in patients with PAD. Both subjective and objective measurement methods can be used for determining the level of walking capacity in the patients with PAD.

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.

Arterial Doppler Waveforms Are Independently Associated With Maximal Walking Distance in Suspected Peripheral Artery Disease Patients

Objective: Arterial Doppler waveform recordings are commonly used to assess lower extremity arterial disease (LEAD) severity. However, little is known about the relationship between arterial Doppler waveform profiles and patients' walking capacity. The purpose of this study was to assess whether arterial Doppler waveforms are independently associated with maximal walking distance (MWD) in patients experiencing exertional limb symptoms. Materials and Methods: This cross-sectional study included suspected LEAD patients experiencing exertional limb symptoms. In both lower extremities, arterial Doppler waveforms and ankle-brachial index (ABI) values were obtained from the pedis and tibial posterior arteries. Each arterial flow measurement was ranked using the Saint-Bonnet classification system. Treadmill stress testing (3.2 km/h, 10% slope) coupled with exercise oximetry (Exercise-TcPO2) were used to determine MWD. Delta from rest oxygen pressure (DROP) was calculated. Following treadmill stress testing, post-exercise ABI values were recorded. Univariate and multivariate analyses were used to determine the clinical variables associated with MWD. Results: 186 patients experiencing exertional limb symptoms (62 ± 12 years and 26.8 ± 4.5 kg/m2) were included between May 2016 and June 2019. Median [25th; 75th] treadmill MWD was 235 [125;500]m. Better arterial Doppler waveforms were associated with better walking distance (p = 0.0012). Whereas, median MWD was 524 [185;525]m in the group that yielded the best Doppler waveforms, it was 182 [125,305]m in the group with the poorest Doppler waveforms (p = 0.0012). MWD was significantly better (p = 0.006) in the patients with the best ABIs. However, arterial Doppler waveforms alone were significantly associated with MWD (p = 0.0009) in the multivariate model. When exercise variables (post-exercise ABI or DROP) were incorporated into the multivariate model, these were the only variables to be associated with MWD. Conclusion: Of the various clinical parameters at rest, Doppler flow waveform profiles were associated with MWD in suspected LEAD patients. A stronger link was however found between exercise variables and MWD.

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.

Predictors of Improved Walking after a Supervised Walking Exercise Program in Men and Women with Peripheral Artery Disease

We compared the changes in ambulatory outcomes between men and women with symptomatic peripheral arterial disease (PAD) following completion of a supervised, on-site, treadmill exercise program, and we determined whether exercise training variables and baseline clinical characteristics were predictive of changes in ambulatory outcomes in men and women. Twenty-three men and 25 women completed the supervised exercise program, consisting of intermittent walking to mild-to-moderate claudication pain for three months. Men and women significantly increased claudication onset time (COT) (p < 0.001 and p < 0.01, resp.) and peak walking time (PWT) (p < 0.001 for each group). However, change in PWT was less in women (54%) than in men (77%) (p < 0.05). Neither group significantly changed 6-minute walk distance (6MWD). In women, baseline COT was the only predictor for the change in COT (p = 0.007) and the change in PWT (p = 0.094). In men, baseline COT (p < 0.01) and obesity (p < 0.10) were predictors for the change in COT, and obesity was the only predictor for the change in PWT (p = 0.002). Following a supervised, on-site, treadmill exercise program, women had less improvement in PWT than men, and neither men nor women improved submaximal, overground 6MWD. Furthermore, obese men and patients with lower baseline COT were least responsive to supervised exercise. This trial is registered with ClinicalTrial.gov, unique identifier: NCT00618670.

V.O2 Kinetics and clinical factors among patients with peripheral artery disease

PURPOSE

To investigate the association between oxygen uptake (V.O2) kinetics and demographic, behavioral, and clinical factors among patients with peripheral artery disease (PAD).

METHODS

A total of 85 PAD patients with intermittent claudication performed a constant load treadmill test, and breath-by-breath (V.e.)O2 was obtained to assess V.O2 kinetics. Demographic information, anthropometry, cardiovascular risk factors, and comorbid conditions were recorded.

RESULTS

Using univariate analyses, higher values of tau ([τ], i.e., slowed V.O2 kinetics) were associated with female gender, non-Caucasian race, hypertension, dyslipidemia, and age ≤66 years. Smoking, diabetes, obesity, metabolic syndrome, height, and ankle brachial index were not significantly related to V.O2 kinetics. Using multiple regression procedures, the identified predictors of slowed V.O2 kinetics were female gender (4.76 [95% CI: 1.49-8.03] seconds; P = .0049), non-Caucasian race (4.70 [95% CI: 1.29-8.12] seconds; P = .0075), hypertension (12.06 [95% CI: 8.83-15.28] seconds; P < .0001), and age ≤66 years (4.97 [95% CI: 1.95-7.99] seconds; P = .0015).

CONCLUSIONS

In PAD patients, slowed V.O2 kinetics are associated with demographic and clinical factors. The clinical significance is that female, non-Caucasian, and hypertensive PAD patients present central and/or peripheral limitations that may partially account for their walking impairment.

Predictors of walking capacity in peripheral arterial disease patients

OBJECTIVE

To estimate walking capacity in intermittent claudication patients through a prediction model based on clinical characteristics and the walking impairment questionnaire.

METHODS

The sample included 133 intermittent claudication patients of both genders aged between 30 and 80 years. Data regarding clinical characteristics, the walking impairment questionnaire and treadmill walking test performance were obtained. Multiple regression modeling was conducted to predict claudication onset distance and total walking distance using clinical characteristics (age, height, mass, body mass index, ankle brachial index lower, gender, history of smoking and co-morbid conditions) and walking impairment questionnaire responses. Comparisons of claudication onset distance and total walking distance measured during treadmill tests and estimated by a regression equation were performed using paired t-tests.

RESULTS

Co-morbid conditions (diabetes and coronary artery disease) and questions related to difficulty in walking short distances (walking indoors - such as around your house and walking 5 blocks) and at low speed (walking 1 block at average speed - usual pace) resulted in the development of new prediction models high significant for claudication onset distance and total walking distance (p<0.001). In addition, non-significant differences from the results obtained by the treadmill test and estimated by the current model (p>0.05) were observed.

CONCLUSION

The current study demonstrated that walking capacity can be adequately estimated based on co-morbid conditions and responses to the walking impairment questionnaire.

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.

The effects of including quality of life responses in models to predict walking performance of patients with intermittent claudication

OBJECTIVES

To examine the accuracy of previously developed prediction models of treadmill walking performance in patients with intermittent claudication (IC) due to peripheral arterial disease (PAD); and to examine the accuracy of new prediction models.

DESIGN

Analysis of data collected in a previous randomised clinical trial.

MATERIALS

Ninety-three assessments of 28 patients diagnosed with IC due to PAD.

METHODS

Patients undertook routine clinical assessments, quality of life (QOL) questionnaires and treadmill walking tests. Walking performance and estimates based on prediction models were compared via paired t-tests or Wilcoxon Rank Sum tests. Stepwise linear regression generated models to predict walking performance from clinical measures and QOL responses. Accuracy was determined as the absolute error between model estimates and patient results.

RESULTS

Walking performance was significantly underestimated (35-71% error) by previously developed prediction models. Models developed in the current study identified QOL responses as the most significant predictors of current walking performance but these models still resulted in substantial errors (19-84%).

CONCLUSIONS

Previously published predictors of walking performance significantly underestimated patient's ability in practise. Predictions based upon clinical measurements and QOL responses were developed however, their accuracy was also limited. Further research is needed regarding walking performance prediction to assist clinicians with assessment of PAD severity and treatment effectiveness.

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.

Association between daily ambulatory activity patterns and exercise performance in patients with intermittent claudication

PURPOSE

To determine the association between daily ambulatory activity patterns and exercise performance in patients with intermittent claudication.

METHODS

One hundred thirty-three patients limited by intermittent claudication participated in this study. Patients were assessed on their ambulatory activity patterns for 1 week with a small, lightweight step activity monitor attached to the ankle using elastic velcro straps above the lateral malleolus of the right leg. The step activity monitor recorded the number of strides taken on a minute-to-minute basis and the time spent ambulating. Patients also were characterized on ankle-brachial index (ABI), ischemic window (IW) after a treadmill test, as well as initial claudication distance (ICD), and absolute claudication distance (ACD) during treadmill exercise.

RESULTS

The patient characteristics (mean +/- SD) were as follows: ABI = 0.71 +/- 0.23, IW = 0.54 +/- 0.72 mm Hg.min.meter(-1), ICD = 236 +/- 198 meters, and ACD = 424 +/- 285 meters. The patients took 3366 +/- 1694 strides/day, and were active for 272 +/- 103 min/day. The cadence for the 30 highest, consecutive minutes of each day (15.1 +/- 7.2 strides/min) was correlated with ICD (r = 0.316, P < .001) and ACD (r = 0.471, P < 0.001), and the cadence for the 60 highest, consecutive minutes of each day (11.1 +/- 5.4 strides/min) was correlated with ICD (r = 0.290, P < .01) and ACD (r = 0.453, P < .001). Similarly, the cadences for the highest 1, 5, and 20 consecutive minutes, and the cadence for the 30 highest, nonconsecutive minutes all were correlated with ICD and ACD (P < .05). None of the ambulatory cadences were correlated with ABI (P > .05) or with ischemic window (P > .05).

CONCLUSION

Daily ambulatory cadences are associated with severity of intermittent claudication, as measured by ACD and ICD, but not with peripheral hemodynamic measures.

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

PURPOSE

This study was conducted to determine the association between the characteristics of calf muscle hemoglobin oxygen saturation (StO(2)) and exercise performance in patients with intermittent claudication.

METHODS

The study comprised 39 patients 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

Calf muscle StO(2) decreased 72%, from 55% +/- 18% (mean +/- SD) saturation at rest to the minimum value of 17% +/- 19% saturation attained 459 +/- 380 seconds after the initiation of exercise. After exercise, recovery half-time of calf muscle StO(2) was attained at 129 +/- 98 seconds, whereas full recovery to the resting value was reached at 225 +/- 140 seconds. After adjusting for sex, race, and grouping according to the initial decline constant in calf muscle StO(2) during exercise, the exercise time to minimum calf muscle StO(2) was correlated with the ischemic window (r = -0.493, P = .002), ICD (r = 0.339, P = .043), and ACD (r = 0.680, P < .001). After treadmill exercise, the recovery half-time of calf muscle StO(2) was correlated with the ischemic window (r = 0.531, P < .001), ICD (r = -0.598, P < .001), and ACD (r = -0.491, P = .003).

CONCLUSION

In patients limited by intermittent claudication, shorter ICD and ACD values are associated with reaching a minimum value in calf muscle StO(2) sooner during treadmill exercise and with having a delayed recovery in calf muscle StO(2) after exercise.

The effect of metabolic syndrome components on exercise performance in patients with intermittent claudication

PURPOSE

To determine the effect of metabolic syndrome components on intermittent claudication, physical function, health-related quality of life, and peripheral circulation in patients with peripheral arterial disease (PAD), and to identify the metabolic syndrome components most predictive of each outcome measure.

METHODS

Patients limited by intermittent claudication with three (n = 48), four (n = 45), or five (n = 40) components of metabolic syndrome were studied. Patients were assessed on PAD-specific measures consisting of ankle-brachial index (ABI), initial claudication distance, absolute claudication distance, physical function measures, health-related quality of life, and calf blood flow and transcutaneous oxygen tension responses after 3 minutes of vascular occlusion.

RESULTS

Initial claudication distance (mean +/- SD) progressively declined (P = .019) in those with three (203 +/- 167 m), four (124 +/- 77 m), and five (78 +/- 57 m) metabolic syndrome components, and absolute claudication distance progressively declined (P = .036) in these groups as well (414 +/- 224 m vs 323 +/- 153 m vs 249 +/- 152 m, respectively). Furthermore, compared with patients with only three components of metabolic syndrome, those with all five components had impaired values (P < .05) for peak oxygen uptake, ischemic window, 6-minute walk distance, self-perceived walking ability and health, daily physical activity, health-related quality of life on six of eight domains, calf hyperemia, and calf ischemia after vascular occlusion. Abdominal obesity was the predictor (P < .05) of exercise performance during the treadmill and 6-minute walk tests, as well as physical activity. Elevated fasting glucose was the predictor (P < .05) of peripheral vascular measures, self-perceived walking ability and health, and health-related quality of life.

CONCLUSION

PAD patients with more metabolic syndrome components have worsened intermittent claudication, physical function, health-related quality of life, and peripheral circulation. Abdominal obesity and elevated fasting glucose are the metabolic syndrome components that are most predictive of these outcome measures. Aggressively treating these metabolic syndrome components may be particularly important in managing symptoms and long-term prognosis of PAD patients.

Patterns of ambulatory activity in subjects with and without intermittent claudication

PURPOSE

This study compared the patterns of ambulatory activity in subjects with and without intermittent claudication.

METHODS

The study participants were 98 subjects limited by intermittent claudication and 129 controls who were matched for age, gender, and race. Subjects were assessed on their ambulatory activity patterns for 1 week with a small, lightweight step activity monitor attached to the ankle using elastic Velcro (Velcro Industries BV, Manchester, NH) straps above the lateral malleolus of the right leg. The step activity monitor recorded the number of strides taken on a minute-to-minute basis, the time spent ambulating, and the time and number of strides measured at low (<15 strides/min), medium (15 to 30 strides/min), and high (>30 strides/min) cadences.

RESULTS

Subjects with intermittent claudication took fewer total strides each day than the controls (3149 +/- 1557 strides/d vs 4230 +/- 1708 strides/d; P < .001) and fewer strides at medium (1228 +/- 660 strides/day vs 1638 +/- 724 strides/day; P = .001) and high (766 +/- 753 strides/day vs 1285 +/- 1029 strides/day; P < .001) cadences. Subjects with intermittent claudication also had a lower daily average cadence than the controls (11.8 +/- 2.9 strides/min vs 13.5 +/- 3.1 strides/min; P < .001) and spent less total time ambulating each day (264 +/- 109 min/day vs 312 +/- 96 min/day; P = .034), primarily at medium (58 +/- 30 min/day vs 75 +/- 32 min/day; P < .001) and at high (19 +/- 17 min/day vs 30 +/- 22 min/day; P = .001) cadences.

CONCLUSION

Intermittent claudication is associated with lower total daily ambulatory activity owing both to less time ambulating and to fewer strides taken while ambulating, particularly at moderate and high cadences.

Exercise performance in patients with peripheral arterial disease who have different types of exertional leg pain

OBJECTIVE

This study compared the exercise performance of patients with peripheral arterial disease (PAD) who have different types of exertional leg pain.

METHODS

Patients with PAD were classified into one of four groups according to the San Diego Claudication Questionnaire: intermittent claudication (n = 406), atypical exertional leg pain causing patients to stop (n = 125), atypical exertional leg pain in which patients were able to continue walking (n = 81), and leg pain on exertion and rest (n = 103). Patients were assessed on the primary outcome measures of ankle-brachial index (ABI), treadmill exercise measures, and ischemic window.

RESULTS

All patients experienced leg pain consistent with intermittent claudication during a standardized treadmill test. The mean (+/- SD) initial claudication distance (ICD) was similar (P = .642) among patients with intermittent claudication (168 +/- 160 meters), atypical exertional leg pain causing patients to stop (157 +/- 130 meters), atypical exertional leg pain in which patients were able to continue walking (180 +/- 149 meters), and leg pain on exertion and rest (151 +/- 136 meters). The absolute claudication distance (ACD) was similar (P = .648) in the four respective groups (382 +/- 232, 378 +/- 237, 400 +/- 245, and 369 +/- 236 meters). Similarly, the ischemic window, expressed as the area under the curve (AUC) after treadmill exercise, was similar (P = .863) in these groups (189 +/- 137, 208 +/- 183, 193 +/- 143, and 199 +/- 119 AUC).

CONCLUSION

PAD patients with different types of exertional leg pain, all limited by intermittent claudication during a standardized treadmill test, were remarkably similar in ICD, ACD, and ischemic window. Thus, the presence of ambulatory symptoms should be of primary clinical concern in evaluating PAD patients regardless of whether they are consistent with classic intermittent claudication.

The relationship between ankle-brachial index and leisure-time physical activity in patients with intermittent claudication

The purpose of the study was to examine the relationship between ankle-brachial index (ABI) and leisure-time physical activity (LTPA) in patients with peripheral arterial disease limited by intermittent claudication. Patients included 342 sedentary men and women between the ages of 45 and 85 with intermittent claudication confirmed by a resting ABI of less than 0.90. Patients were categorized into either a low ABI group (ABI <0.50; n=84), a middle ABI group (ABI = 0.50 to 0.69; n=164), or a high ABI group (ABI = 0.70 to 0.89; n=94). The Minnesota LTPA questionnaire was used to estimate physical activity patterns, and a treadmill test, 6- minute walk test, and Walking Impairment Questionnaire were used to measure ambulatory function. A progressive decrease (p=0.030) in the total LTPA was observed among the high ABI (180 +/-131 kcal/day; mean +/- SD), middle ABI (138 +/-127 kcal/day), and low ABI (110 +/-89 kcal/day) groups. Progressive decrements in LTPA spent at moderate intensity (p=0.016) and high intensity (p=0.009), as well as the mean intensity of LTPA (p=0.024) were observed among the three respective ABI groups. Group differences in the LTPA measurements were no longer present (p>0.05) after adjusting for group differences in the absolute claudication distance during a treadmill test, and the 6-minute walk distance. The decline in total daily LTPA with progressively lower ABI in patients with intermittent claudication was due to their decreased participation in physical activities requiring moderate and high intensities. In addition, group differences in the LTPA measurements were explained by differences in ambulatory function.

Metabolic syndrome impairs physical function, health-related quality of life, and peripheral circulation in patients with intermittent claudication

PURPOSE

This study was conducted to (1) examine the effect of metabolic syndrome on intermittent claudication, physical function, health-related quality of life, and peripheral circulation in patients with peripheral arterial disease (PAD), and (2) determine whether peripheral vascular function was predictive of intermittent claudication and physical function in patients with metabolic syndrome.

METHODS

Patients limited by intermittent claudication and who had metabolic syndrome (n = 133) were compared with those without metabolic syndrome (n = 201). Patients were assessed on metabolic syndrome characteristics, PAD-specific measures consisting of ankle/brachial index and claudication distances, physical function measures, health-related quality of life, and calf blood flow and transcutaneous oxygen tension responses after 3 minutes of vascular occlusion.

RESULTS

Initial claudication distance (mean +/- SD) was 29% shorter (P = .018) in patients with metabolic syndrome than in the controls (128 +/- 121 meters vs 180 +/- 166 meters), and absolute claudication distance was 22% shorter (P = .025) in those with metabolic syndrome (319 +/- 195 meters vs 409 +/- 255 meters). Furthermore, patients with metabolic syndrome had lower peak oxygen uptake (P = .037), a shorter 6-minute walk distance (P = .027), lower values on six domains of health-related quality of life (P < .05), reduced calf hyperemia (P = .028), and greater calf ischemia (P < .001) after vascular occlusion. In the group with metabolic syndrome, calf ischemia was correlated with initial claudication distance (r = 0.30, P = .004), absolute claudication distance (r = 0.40, P < .001), and peak oxygen uptake (r = 0.52, P < .001).

CONCLUSION

Metabolic syndrome worsens intermittent claudication, physical function, health-related quality of life, and peripheral circulation in patients with PAD. Calf ischemia in those with metabolic syndrome was predictive of intermittent claudication and physical function. The additive burden of metabolic syndrome thus places patients who are limited by intermittent claudication at an even greater risk for living a functionally dependent lifestyle. Aggressive risk-factor modification designed to treat components of metabolic syndrome should be evaluated for efficacy in modifying physical and vascular function in patients with intermittent claudication.

Exercise training enhances endogenous fibrinolysis in peripheral arterial disease

PURPOSE

Acute clinical events resulting from atherosclerosis (myocardial infarction, stroke) are associated with impaired endogenous fibrinolysis, the system by which the body lyses inappropriately formed thrombus. Endurance exercise training improves fibrinolysis in normal subjects and those with coronary artery disease. The hypothesis of this study was that exercise training would improve fibrinolysis in subjects with peripheral arterial disease (PAD).

METHODS AND RESULTS

Twenty-one men with intermittent claudication (IC-EX) underwent treadmill exercise training for 6 months. Twenty age-matched male subjects with IC were followed for the same period (IC-NONEX). Fibrinolytic activity was measured prior to entry into exercise or "usual care," and at the completion of the study period. Fibrinolysis was quantified by measurement of the activity levels of tissue plasminogen activator (tPA, the activator of fibrinolysis) and its inhibitor plasminogen activator inhibitor-1 (PAI-1), using an amidolytic method. Fibrinolysis, quantified as increased PAI-1 activity, was reduced in both claudicant groups relative to healthy controls at baseline. After 6 months of exercise, subjects in the IC-EX group experienced significant improvements in fibrinolytic activity, manifested as a 23% decrease in PAI-1 activity and a 28% increase in tPA activity. No changes occurred in the IC-NONEX group. In the IC-EX group, subjects with the highest initial PAI-1 values experienced the greatest decreases in PAI-1 activity and thus the greatest benefit from exercise.

CONCLUSIONS

Patients with PAD have impaired fibrinolytic activity, manifested primarily as increases in the inhibitor of fibrinolysis, PAI-1. Six months of exercise training reduced these impairments, and may serve as an intervention to reduce cardiovascular mortality and morbidity in these patients.

Determinants of peak V(O2) in peripheral arterial occlusive disease patients

Peripheral arterial occlusive disease (PAOD) patients with intermittent claudication are functionally limited and deconditioned. This study examined whether peak aerobic capacity (V(O2) peak) was associated with PAOD severity, muscle mass, and comorbidities in 109 PAOD patients (93 men and 16 women) aged 48-86 years. The V(O2) peak (1.12+/-0.34 L/min), percentage body fat (30.6+/-8.3%), lean tissue mass of the total body (51.4+/-8.4 kg), lean tissue mass of the legs (16.6+/-3.0 kg), and appendicular skeletal mass (22.8+/-4.2 kg) were determined. The lean tissue mass of the total body (r = .44), lean tissue of the legs (r = .43) and resting ankle/brachial systolic pressure index (ABI; r = .41) correlated with peak V(O2) (all p < .001). None of the comorbidity variables (obesity, arthritis, coronary artery disease, hypertension, diabetes, and smoking history) were significantly associated with peak V(O2) except smoking status. The final model for the prediction of peak V(O2) included lean tissue mass of the legs, resting ABI, smoking status, and ABI x smoking status (r2 = .37,p < .001). In older patients with intermittent claudication, lean tissue mass is an important determinant of physical performance independent of PAOD severity and smoking status. Prevention of muscle atrophy may preserve ambulatory function and peak exercise capacity in older PAOD patients.

Pneumatic ankle tourniquets: physiological factors related to minimal arterial occlusion pressure

This study investigates several physiological measurements for their correlation to the minimal arterial occlusion pressure using the pneumatic ankle tourniquet. Blood pressure (brachial), height, weight, body fat percentage, ankle circumference, and leg circumference measurements were collected from 50 normotensive healthy subjects. Ankle brachial index (ABI) was also compared. A pneumatic ankle tourniquet was applied to the right ankle and inflated until Doppler insonation confirmed that arterial occlusion had occurred. Mean arterial occlusion pressure was 161.7 mm Hg (N = 50, Nmales = 33, Nfemales = 17), and statistically less than 170 mm Hg (p < .05). The authors present a data model to predict the lowest necessary ankle tourniquet pressure for this study group. Forward stepwise linear regression (critical significance = .01) yields two variables, ankle brachial index and systolic blood pressure, which are used to predict occlusion pressure in this study group.

Cigarette smoking shortens the duration of daily leisure time physical activity in patients with intermittent claudication

PURPOSE

The authors determined (1) whether peripheral arterial occlusive disease (PAOD) patients who smoke have a reduction in either the duration or intensity of daily physical activities compared with nonsmoking patients, and (2) whether group differences in the pattern of physical activity persisted after controlling for potential confounding variables.

METHODS

A total of 170 smokers and 201 nonsmokers who had quit smoking for at least 1 year prior to investigation were studied. Physical activity patterns were measured using the Minnesota Leisure Time Physical Activity (LTPA) questionnaire. Patients also were characterized on potential covariates such as demographics, comorbid conditions, cardiovascular risk factors, ambulatory measures, peripheral hemodynamics, and anthropometric measures.

RESULTS

The smokers were 37% less physically active than the nonsmokers (87 +/- 90 versus 139 +/- 121 kcal/day; P = 0.027). The reduced total LTPA in the smokers was due to a 28% shorter duration of performing activities (26 +/- 7 versus 36 +/- 22 min/day; P = 0.031), and a 3% lower mean intensity of the activities (3.3 +/- 1.0 versus 3.8 +/- 0.8 kcal/min; P = 0.038). The distance score on the Walking Impairment Questionnaire and the hip circumference were significant covariates of the LTPA measures. After adjusting for these covariates, the total LTPA remained 29% lower in the smokers (P = 0.039), the mean daily duration of LTPA remained 20% lower (P = 0.043), but the mean intensity of LTPA was no longer different between the groups.

CONCLUSION

Compared with their nonsmoking counterparts, claudicants who smoke have a reduced total LTPA because they engage in activities of similar intensity for a shorter duration of time.

The effect of indirect calorimetry measurement on claudication pain in patients with peripheral arterial occlusive disease

The effect of indirect calorimetry measurement on the duration to onset and maximal claudication pain and hemodynamic measures was evaluated. Fifteen male patients with peripheral arterial occlusive disease (PAOD) performed two graded exercise tests (GXTs) in random order, one with and the other without the use of indirect calorimetry measurement. During the tests the time to onset and maximal claudication pain was recorded. Before and after the tests, ankle/brachial systolic pressure index (ABI) was determined. The time to onset of claudication pain was shorter for the test with indirect calorimetry (4:49+/-3:50 vs 5:44+/-4:39 min:sec, p < 0.005). Time to maximal claudication pain was not significantly different between the two conditions (8:58+/-3:01 min:sec with indirect calorimetry, 9:39+/-3:36 min:sec, without). There were no significant differences in ABI between the two testing sessions at any time point. Results of this study suggest that indirect calorimetry measurement can be utilized without compromising maximal claudication pain time or hemodynamic measurements but that time to onset of claudication pain is hastened with indirect calorimetry measurement in patients with PAOD.

Prediction of peak oxygen consumption in patients with intermittent claudication

Determination of peak oxygen consumption (VO2peak) is considered important for assessing a patient's functional capacity and for exercise prescription. However, the equipment necessary to obtain accurate determination of VO2peak is not always available in clinical settings. The present study sought to develop an equation to estimate VO2peak in peripheral arterial occlusive disease (PAOD) patients with intermittent claudication and to determine independent predictors of VO2peak in this population. One hundred and fifty-seven patients with intermittent claudication were assigned to either a validation group (n = 105) or a cross-validation group (n = 52). Medical history, height, weight, body mass index (BMI), age, gender, smoking status, resting and postexercise ankle/brachial systolic pressure index (ABI), and time to maximal claudication pain and maximal heart rate from an incremental graded exercise test (GXT) were used as potential independent predictors of VO2peak. Time to onset of maximal claudication pain, maximal heart rate, and BMI were all independently associated with VO2peak. These variables were used to estimate VO2peak by the following equation: VO2peak (mL/kg/min) = (0.00872 x maximal claudication pain time [sec]) + (0.02839 x maximal heart rate [b/min]) - (0.12034 x BMI) + 10.11411 r = 0.71, r2 = 0.50, standard error of estimate = 2.02 mL/kg/min, p < 0.0001There was no significant difference between the estimated and actual VO2peak in the cross-validation group, and the coefficient of variation between estimated and actual VO2peak in this group was 18.3%. There was no significant difference between the correlation coefficient for the relationship between estimated and actual VO2peak in the cross-validation group (r = 0.61) and the multiple correlation coefficient from the validation group (r = 0.71). Results of this study suggest that a multiple regression equation can be used to estimate VO2peak in patients with intermittent claudication by measuring time to maximal claudication pain and maximal heart rate from a GXT and by measuring BMI.

The clinical utility of a six-minute walk test in peripheral arterial occlusive disease patients

OBJECTIVES

To determine the test-retest reliability of the distance covered and the steps taken to complete a 6-minute walk test by peripheral arterial occlusive disease (PAOD) patients with intermittent claudication. To determine the relationship between the total distance and steps covered during the 6-minute walk test and clinical measures of PAOD severity.

DESIGN

Cross-sectional design.

SETTING

The Claude Pepper Older Americans Independence Center at the University of Maryland at Baltimore.

PARTICIPANTS

Sixty-four PAOD patients between the ages of 45 and 88 years (age = 68 +/- 7 years, ankle/brachial index (ABI) = .61 +/- .19) were recruited from the Vascular Clinic at the Baltimore Veterans Affairs Medical Center and from radio and newspaper advertisements.

MEASUREMENTS

Patients were assessed on a 6-minute walk test and a treadmill graded exercise test. A second 6-minute walk test was administered approximately 1 week later. Patients also were characterized in regard to blood pressure in the arms and legs, ABI, anthropometry, body composition, and physical activity.

RESULTS

The distances walked during the two 6-minute walk tests were similar (350 +/- 78 m vs 360 +/- 73 m), resulting in a high reliability coefficient (R = .94) and a low coefficient of variation (10.4%). The total steps taken during the 6-minute walk test also were similar (562 +/- 113 steps vs 587 +/- 107 steps), resulting in a high reliability coefficient (R = .90) and a low coefficient of variation (11.7%). Furthermore, the 6-minute walking distance correlated with the distances to onset (r = .346, P = .007) and with maximal claudication pain (r = .525, P < .001) during the treadmill test as well as with ABI (r = .552, P < .001).

CONCLUSION

The 6-minute walk test yields highly reliable measurements, which are related to the functional and hemodynamic severity of PAOD, in patients with intermittent claudication.

Relationship between free-living daily physical activity and ambulatory measures in older claudicants

The purpose of this study was to determine the relationship between free-living daily physical activity and ambulatory measurements in peripheral arterial occlusive disease (PAOD) patients with intermittent claudication. Thirty-four older, nonsmoking PAOD patients with intermittent claudication (age=69.0 +/- 6.0 years, ankle/brachial index [ABI] =0.63 +/- 0.18) were recruited from the Vascular Clinic at the Baltimore Veterans Affairs Medical Center and from radio and newspaper advertisements. Energy expenditure of physical activity (EEPA) was determined by using doubly labeled water and indirect calorimetry techniques. Patients were also characterized on claudication distances and peak oxygen uptake during a graded treadmill test, 6-minute walking distance, weight, body mass index, and percent body fat. The claudication patients were sedentary, as EEPA was 362 +/- 266 kcal/day. EEPA was related to the 6-minute walk distance (369 +/- 68 meters; r=0.629, P<0.001), to the number of steps taken during 6 minutes (605 +/- 99 steps; r=0.485, P=0.008), to the treadmill distance to maximal claudication (313 +/- 131 meters; r=0.470, P=0.010), and to the time to relief of pain (6:21 +/- 3:57 min:sec; r=-0.417, P=0.017). None of the other ambulatory and body composition measurements were correlated with EEPA. In conclusion, a reduction in free-living daily physical activity was associated with a decrease in ambulatory ability and with more severe intermittent claudication in older PAOD patients.

The effect of cigarette smoking on free-living daily physical activity in older claudication patients

The purposes of this study were (1) to determine whether peripheral arterial occlusive disease (PAOD) patients who smoke have a lower free-living daily physical activity than nonsmoking patients and (2) to determine whether the difference in physical activity persisted after controlling for potential confounders such as PAOD severity, age, body composition, and peripheral circulation. Thirty-four smokers (45.5 +/-9.8 years of smoking) and 43 nonsmokers (former smokers who had a smoking history of 35.0 +/- 13.1 years who quit 12.2 +/- 10.5 years prior to investigation) were studied. Patients wore a Caltrac accelerometer and a pedometer on each hip over two consecutive weekdays to assess free-living daily physical activity. Patients were also characterized on age, weight, body mass index (BMI), percent body fat, ankle/brachial index (ABI), calf blood flow, and exercise capacity. The smoking and nonsmoking claudication patients had a similar level of PAOD severity, for no group differences were noted in ABI (P=0.287) and treadmill time to maximal claudication pain (P=0.201). However, the smokers were 35% less physically active than the nonsmokers (264 +/- 123 vs 407 +/- 272 kcal/day; P<0.006), and they took 23% fewer steps (4,116 +/- 2,199 vs 5,329 +/- 2,924 steps/day; P<0.034). After adjustment for group differences in age, weight, BMI, percent body fat, and calf blood flow, the lower activity level of the smokers persisted. The adjusted daily energy expenditure was 27% lower (292 +/- 105 vs 400 +/- 214 kcal/day; P=0.021), and the adjusted amount of daily walking was 29% lower (4,039 +/- 1,760 vs 5,684 +/- 2,235 steps/day; P=0.003). Smoking PAOD patients had a less physically active lifestyle than nonsmoking patients, and the lower activity level of the smokers was independent of PAOD severity, age, body composition, and peripheral circulation.