Pulmonary V̇o2 dynamics during treadmill and arm exercise in peripheral arterial disease

Physical activity, cardiorespiratory fitness, and cardiovascular health: A clinical practice statement of the American Society for Preventive Cardiology Part II: Physical activity, cardiorespiratory fitness, minimum and goal intensities for exercise training, prescriptive methods, and special patient populations

The prescription of exercise for individuals with and without cardiovascular disease (CVD) should be scientifically-based yet adapted to the patient. This scientific statement reviews the clinical and physiologic basis for the prescription of exercise, with specific reference to the volume of physical activity (PA) and level of cardiorespiratory fitness (CRF) that confer significant and optimal cardioprotective benefits. Recommendations are provided regarding the appropriate intensity, frequency, and duration of training; the concept of MET-minutes per week; critical components of the exercise session (warm-up, conditioning phase, cool-down); methodologies for establishing the training intensity, including oxygen uptake reserve (V̇O2R), target heart rate derivation and rating perceived exertion; minimum and goal intensities for exercise training; and, types of training activities, including resistance training, adjunctive lifestyle PA, marathon/triathlon training, and high-intensity interval training. In addition, we discuss the rationale for and value of exercise training programs for patients with peripheral artery disease, diabetes mellitus, and heart failure.

Oxygen uptake kinetics and chronotropic responses to exercise are impaired in survivors of severe COVID-19

The post-acute phase of coronavirus disease 2019 (COVID-19) is often marked by several persistent symptoms and exertional intolerance, which compromise survivors’ exercise capacity. This was a cross-sectional study aiming to investigate the impact of COVID-19 on oxygen uptake (V̇o₂) kinetics and cardiopulmonary function in survivors of severe COVID-19 about 3–6 mo after intensive care unit (ICU) hospitalization. Thirty-five COVID-19 survivors previously admitted to ICU (5 ± 1 mo after hospital discharge) and 18 controls matched for sex, age, comorbidities, and physical activity level with no prior history of SARS-CoV-2 infection were recruited. Subjects were submitted to a maximum-graded cardiopulmonary exercise test (CPX) with an initial 3-min period of a constant, moderate-intensity walk (i.e., below ventilatory threshold, VT). V̇o₂ kinetics was remarkably impaired in COVID-19 survivors as evidenced at the on-transient by an 85% (P = 0.008) and 28% (P = 0.001) greater oxygen deficit and mean response time (MRT), respectively. Furthermore, COVID-19 survivors showed an 11% longer (P = 0.046) half-time of recovery of V̇o₂ (T_1/2V̇o₂) at the off-transient. CPX also revealed cardiopulmonary impairments following COVID-19. Peak oxygen uptake (V̇o_2peak), percent-predicted V̇o_2peak, and V̇o₂ at the ventilatory threshold (V̇o_2VT) were reduced by 17%, 17%, and 12% in COVID-19 survivors, respectively (all P < 0.05). None of the ventilatory parameters differed between groups (all P > 0.05). In addition, COVID-19 survivors also presented with blunted chronotropic responses (i.e., chronotropic index, maximum heart rate, and heart rate recovery; all P < 0.05). These findings suggest that COVID-19 negatively affects central (chronotropic) and peripheral (metabolic) factors that impair the rate at which V̇o₂ is adjusted to changes in energy demands.

NEW & NOTEWORTHY Our findings provide novel data regarding the impact of COVID-19 on submaximal and maximal cardiopulmonary responses to exercise. We showed that V̇o₂ kinetics is significantly impaired at both the onset (on-transient) and the recovery phase (off-transient) of exercise in these patients. Furthermore, our results suggest that survivors of severe COVID-19 may have a higher metabolic demand at a walking pace. These findings may partly explain the exertional intolerance frequently observed following COVID-19.

Oxygen Uptake Kinetics during Exercise Reveal Central and Peripheral Limitation in Patients with Ilio-Femoral Venous Obstruction

OBJECTIVE

Pulmonary oxygen uptake (V̇O₂) kinetics measured during initiation of exercise mirror energetic transition during daily activity. The aim of this study was to elucidate the pathophysiological mechanisms of exercise limitation of patients with chronic ilio-femoral vein obstruction after deep vein thrombosis by measuring V̇O₂ kinetics compared to patients with peripheral arterial disease (PAD) and healthy individuals.

METHODS

Eleven patients with ilio-femoral vein obstruction (7 man, age 20-65 yrs.), seven patients with PAD (all men, age 44-60 yrs.) and eight healthy participants (5 men, age 28-58 yrs.) were studied. Participants performed upper and lower-limb symptom-limited cardiopulmonary exercise tests on cycle ergometers; and four repeat lower-limb tests at a constant work-rate (WR) corresponding to 90% of the gas exchange threshold for determining V̇O₂ kinetics.

RESULTS

Phase I V̇O₂ amplitude in the constant WR tests (% increase over resting V̇O₂), representing the initial surge in cardiac output caused by the emptying of leg veins, was 59±19% in the ilio-femoral vein obstruction group, 73±22% in peripheral arterial disease and 85±26% in healthy participants (p=0.055 for ilio-femoral vein obstruction vs. healthy). Phase II V̇O₂ kinetics, which largely reflect the kinetics of O₂ consumption in the exercising muscles, were slower in ilio-femoral vein obstruction (tau = 42±6 s), and PAD (tau = 49±19 s), compared to healthy participants (23±4 s; p<0.01) CONCLUSIONS: Slow phase II V̇O₂ kinetics reflect a slow onset of muscular aerobic metabolism in both ilio-femoral vein obstruction and PAD. Low amplitude phase I of V̇O₂ kinetics observed in ilio-femoral vein obstruction suggests a damped cardio-dynamic phase, consistent with reduced venous return from the obstructed veins. These abnormalities of V̇O₂ kinetics may contribute to exercise intolerance in ilio-femoral vein obstruction and PAD.

Acute effects of leg heat therapy on walking performance and cardiovascular and inflammatory responses to exercise in patients with peripheral artery disease

Lower-extremity peripheral artery disease (PAD) is associated with increased risk of cardiovascular events and impaired exercise tolerance. We have previously reported that leg heat therapy (HT) applied using liquid-circulating trousers perfused with warm water increases leg blood flow and reduces blood pressure (BP) and the circulating levels of endothelin-1 (ET-1) in patients with symptomatic PAD. In this sham-controlled, randomized, crossover study, sixteen patients with symptomatic PAD (age 65 ± 5.7 years and ankle-brachial index: 0.69 ± 0.1) underwent a single 90-min session of HT or a sham treatment prior to a symptom-limited, graded cardiopulmonary exercise test on the treadmill. The primary outcome was the peak walking time (PWT) during the exercise test. Secondary outcomes included the claudication onset time (COT), resting and exercise BP, calf muscle oxygenation, pulmonary oxygen uptake (V̇O2 ), and plasma levels of ET-1, interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α). Systolic, but not diastolic BP, was significantly lower (~7 mmHg, p < .05) during HT when compared to the sham treatment. There was also a trend for lower SBP throughout the exercise and the recovery period following HT (p = .057). While COT did not differ between treatments (p = .77), PWT tended to increase following HT (CON: 911 ± 69 s, HT: 954 ± 77 s, p = .059). Post-exercise plasma levels of ET-1 were also lower in the HT session (CON: 2.0 ± 0.1, HT: 1.7 ± 0.1, p = .02). Calf muscle oxygenation, V̇O2 , COT, IL-6, and TNF-α did not differ between treatments. A single session of leg HT lowers BP and post-exercise circulating levels of ET-1 and may enhance treadmill walking performance in symptomatic PAD patients.

Combined Aerobic and Resistance Exercise in Walking Performance of Patients With Intermittent Claudication: Systematic Review

Background: The short-term benefits of aerobic and resistance exercise in subjects affected by Peripheral Arterial Disease (PAD) are scarcely examined in interaction. This study aimed to identify the effects of combined aerobic and resistance exercise programs on walking performance compared with isolated aerobic exercise or with the usual care in patients with intermittent claudication.

Methods: A systematic review was conducted following the PRISMA statement. A total of five electronic databases were searched (until October 2019) for randomized and non-randomized controlled trials. The focus comprised PAD patients with intermittent claudication who performed a combined aerobic and resistance exercise program that assessed the walking performance.

Results: Seven studies include combined aerobic and resistance exercise vs. isolated aerobic or vs. usual care. The studies represented a sample size of 337 participants. The follow-up ranged from 4 to 12 weeks, 2 to 5 times-per-week. The risk of bias in the trials was a deemed moderate-to-high risk. After the interventions, the percent change in walking performance outcomes had a large variation. In the combined and isolated aerobic programs, the walking performance always improved, while in the usual care group oscillates between the deterioration and the improvement in all outcomes. Combined exercise and isolated aerobic exercise improved the claudication onset distance from 11 to 396%, and 30 to 422%, the absolute claudication distance from 81 to 197%, and 53 to 121%, and the maximal walking distance around 23 and 10%, respectively.

Conclusions: Currently, there is insufficient evidence about the effects of combined aerobic and resistance exercise compared to isolated aerobic exercise or usual care on walking performance. However, despite the low quality of evidence, the combined aerobic and resistance exercise seems to be an effective strategy to improve walking performance in patients with intermittent claudication. These combined exercise modes or isolated aerobic exercise produce positive and significant results on walking performance. The usual care approach has a trend to deteriorate the walking performance. Thus, given the scarcity of data, new randomized controlled trial studies that include assessments of cardiovascular risk factors are urgently required to better determine the effect of this exercise combination.

The exercise pressor reflex and active O2 transport in peripheral arterial disease

It is unclear if the exaggerated exercise pressor reflex observed in peripheral arterial disease (PAD) patients facilitates Oxygen (O2 ) transport during presymptomatic exercise. Accordingly, this study compared O2 transport between PAD patients and healthy controls during graded presymptomatic work. Seven PAD patients and seven healthy controls performed dynamic plantar flexion in the bore of a 3T MRI scanner. Perfusion, T2 * (an index of relative tissue oxygenation), and SvO2 (a measure of venous oxygen saturation) were collected from the medial gastrocnemius (MG) during the final 10 seconds of each stage. Blood pressure was also collected during the final minute of each stage. As expected, the pressor response to presymptomatic work (4 kg) was exaggerated in PAD patients compared to controls (+14 mmHg ± 4 and +7 mmHg ± 2, P ≤ 0.034). When normalized to changes in free water content (S0 ), T2 * was lower at 2 kg in PAD patients compared to controls (-0.91 Δms/ΔAU ± 0.3 and 0.57 Δms/ΔAU ± 0.3, P ≤ 0.008); followed by a greater increase in perfusion at 4 kg in the PAD group (+18.8 mL/min/100g ± 6.2 vs. -0.21 mL/min/100g ± 3.2 in PAD and controls, P ≤ 0.026). Lastly, SvO2 decreased at 4 kg in both groups (-13% ± 4 and -2% ± 4 in PAD and controls, P ≤ 0.049), suggesting an increase in O2 extraction in the PAD group. Based on these findings, O2 transport appears to be augmented during graded presymptomatic work in PAD patients, and this may be partially mediated by an exaggerated pressor response.

Mobility related physical and functional losses due to aging and disease - a motivation for lower limb exoskeletons

BACKGROUND

Physical and functional losses due to aging and diseases decrease human mobility, independence, and quality of life. This study is aimed at summarizing and quantifying these losses in order to motivate solutions to overcome them with a special focus on the possibilities by using lower limb exoskeletons.

METHODS

A narrative literature review was performed to determine a broad range of mobility-related physical and functional measures that are affected by aging and selected cardiovascular, respiratory, musculoskeletal, and neurological diseases.

RESULTS

The study identified that decreases in limb maximum muscle force and power (33% and 49%, respectively, 25-75 yrs) and in maximum oxygen consumption (40%, 20-80 yrs) occur for older adults compared to young adults. Reaction times more than double (18-90 yrs) and losses in the visual, vestibular, and somatosensory systems were reported. Additionally, we found decreases in steps per day (75%, 60-85 yrs), maximum walking speed (24% 25-75 yrs), and maximum six-minute and self-selected walking speed (38% and 21%, respectively, 20-85 yrs), while we found increases in the number of falls relative to the number of steps per day (800%), injuries due to falls (472%, 30-90 yrs) and deaths caused by fall (4000%, 65-90 yrs). Measures were identified to be worse for individuals with impaired mobility. Additional detrimental effects identified for them were the loss of upright standing and locomotion, freezing in movement, joint stress, pain, and changes in gait patterns.

DISCUSSION

This review shows that aging and chronic conditions result in wide-ranging losses in physical and sensory capabilities. While the impact of these losses are relatively modest for level walking, they become limiting during more demanding tasks such as walking on inclined ground, climbing stairs, or walking over longer periods, and especially when coupled with a debilitating disease. As the physical and functional parameters are closely related, we believe that lost functional capabilities can be indirectly improved by training of the physical capabilities. However, assistive devices can supplement the lost functional capabilities directly by compensating for losses with propulsion, weight support, and balance support.

CONCLUSIONS

Exoskeletons are a new generation of assistive devices that have the potential to provide both, training capabilities and functional compensation, to enhance human mobility.

Translation and Validation of the Brazilian-Portuguese Short Version of Vascular Quality of Life Questionnaire in Peripheral Artery Disease Patients with Intermittent Claudication Symptoms

BACKGROUND

The Vascular Quality of Life Questionnaire (VascuQoL-6) was proposed to evaluate specific quality of life of peripheral artery disease (PAD) patients. However, there is no Brazilian-Portuguese version available, blunting its use in Brazilian patients. The objective of the study was to analyze the psychometric properties of a translated Brazilian-Portuguese version of VascuQoL-6 in Brazilian patients with PAD with intermittent claudication symptoms.

METHODS

One hundred eleven patients with PAD participated in the study. After translation and retranslation, construct validity was analyzed by identifying correlation between VascuQoL-6 scores, general World Health Organization qualify of life (WHOQOL) score, and subjective and objective functional capacity tests. To determine the reliability, internal consistency and test-retest reliability with at least 7 days interval between 2 questionnaire applications were calculated.

RESULTS

Significant correlations between the VascuQoL-6 score and total WHOQOL score (r = 0.44; P < 0.05) were observed. Moreover, we observed negative correlations between the VascuQoL-6 score and 4-meter usual pace (r = -0.33; P < 0.05) and 4-meter fast pace (r = -0.34; P < 0.05) and positive correlation with onset claudication distance (r = 0.39; P < 0.05) and total walking distance (r = 0.29; P ≤ 0.05). Internal consistency was 0.84, whereas the intraclass coefficient correlation was 0.84, with no differences in VascuQoL-6 scores between the 2 applications days.

CONCLUSIONS

The Brazilian-Portuguese version of the VascuQoL-6 presents adequate valid and reliability indicators, allowing its use in patients with PAD with intermittent claudication symptoms.

Skeletal muscle metabolic changes in peripheral arterial disease contribute to exercise intolerance: a point-counterpoint discussion

Patients with claudication have a marked impairment in exercise performance. Several factors contribute to this limitation, including reductions in large vessel blood flow and oxygen delivery as well as metabolic abnormalities in skeletal muscle. The relative contribution of these factors and their role in the pathophysiology of the exercise limitation is discussed using a point-counterpoint approach. Future directions for research conclude the discussion.

Clinical predictors of ventilatory threshold achievement in patients with claudication

PURPOSE

Ventilatory threshold (VT) is considered a clinically important marker of cardiovascular function in several populations, including patients with claudication, because it is related to walking capacity and hemodynamics. The purpose of this study was to identify clinical predictors for VT achievement in patients with intermittent claudication.

METHODS

One hundred and seventy-seven (n = 177) patients with intermittent claudication performed a progressive graded cardiopulmonary treadmill test until maximal claudication pain. Oxygen uptake (V˙O2) was continuously measured during the test, and afterwards, VT was visually detected. Clinical characteristics, demographic data, comorbid conditions, and cardiovascular risk factors were obtained. Patients who achieved and did not achieve VT were compared, as well as the workload that VT occurred in the former group.

RESULTS

VT was achieved in 134 patients (76%), and the mean V˙O2 at VT for these patients was 10.8 ± 2.4 mL·kg(-1)·min(-1). Patients who did not achieve VT presented lower ankle brachial index (ABI), claudication onset time, peak walking time, and V˙O2peak, and the proportion of women was higher compared with patients who achieved VT (P < 0.05). Multiple linear regression analysis identified that sex (b = 0.25, P = 0.002), body mass index (b = -0.18, P = 0.025), peak walking time (b = 0.17, P = 0.044), and ABI (b = 0.23, P = 0.006) were predictors of V˙O2 at VT.

CONCLUSIONS

Forty-three patients (24%) with intermittent claudication did not achieve VT, and these patients were mostly women and those with greater severity of disease. Moreover, in those who reached VT, the predictors of poor VT were female sex, high body mass index, low peak walking time, and low ABI.

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.

Oxygen uptake kinetics

Muscular exercise requires transitions to and from metabolic rates often exceeding an order of magnitude above resting and places prodigious demands on the oxidative machinery and O2-transport pathway. The science of kinetics seeks to characterize the dynamic profiles of the respiratory, cardiovascular, and muscular systems and their integration to resolve the essential control mechanisms of muscle energetics and oxidative function: a goal not feasible using the steady-state response. Essential features of the O2 uptake (VO2) kinetics response are highly conserved across the animal kingdom. For a given metabolic demand, fast VO2 kinetics mandates a smaller O2 deficit, less substrate-level phosphorylation and high exercise tolerance. By the same token, slow VO2 kinetics incurs a high O2 deficit, presents a greater challenge to homeostasis and presages poor exercise tolerance. Compelling evidence supports that, in healthy individuals walking, running, or cycling upright, VO2 kinetics control resides within the exercising muscle(s) and is therefore not dependent upon, or limited by, upstream O2-transport systems. However, disease, aging, and other imposed constraints may redistribute VO2 kinetics control more proximally within the O2-transport system. Greater understanding of VO2 kinetics control and, in particular, its relation to the plasticity of the O2-transport/utilization system is considered important for improving the human condition, not just in athletic populations, but crucially for patients suffering from pathologically slowed VO2 kinetics as well as the burgeoning elderly population.

Exercise: Kinetic considerations for gas exchange

The activities of daily living typically occur at metabolic rates below the maximum rate of aerobic energy production. Such activity is characteristic of the nonsteady state, where energy demands, and consequential physiological responses, are in constant flux. The dynamics of the integrated physiological processes during these activities determine the degree to which exercise can be supported through rates of O₂ utilization and CO₂ clearance appropriate for their demands and, as such, provide a physiological framework for the notion of exercise intensity. The rate at which O₂ exchange responds to meet the changing energy demands of exercise--its kinetics--is dependent on the ability of the pulmonary, circulatory, and muscle bioenergetic systems to respond appropriately. Slow response kinetics in pulmonary O₂ uptake predispose toward a greater necessity for substrate-level energy supply, processes that are limited in their capacity, challenge system homeostasis and hence contribute to exercise intolerance. This review provides a physiological systems perspective of pulmonary gas exchange kinetics: from an integrative view on the control of muscle oxygen consumption kinetics to the dissociation of cellular respiration from its pulmonary expression by the circulatory dynamics and the gas capacitance of the lungs, blood, and tissues. The intensity dependence of gas exchange kinetics is discussed in relation to constant, intermittent, and ramped work rate changes. The influence of heterogeneity in the kinetic matching of O₂ delivery to utilization is presented in reference to exercise tolerance in endurance-trained athletes, the elderly, and patients with chronic heart or lung disease.

Relationship between oxygen consumption kinetics and BODE Index in COPD patients

BACKGROUND AND OBJECTIVE

Patients with chronic obstructive pulmonary disease (COPD) present with reduced exercise capacity due to impaired oxygen consumption (VO(2)), caused primarily by pulmonary dysfunction and deleterious peripheral adaptations. Assuming that COPD patients present with slower VO(2) and heart rate (HR) on-kinetics, we hypothesized that this finding is related to disease severity as measured by the BODE Index. In this context, the present study intends to evaluate the relationship between VO(2) uptake on-kinetics during high-intensity exercise and the BODE Index in patients with COPD.

METHODS

Twenty males with moderate-to-severe stable COPD and 13 healthy control subjects matched by age and sex were evaluated. COPD patients were screened by the BODE Index and then underwent an incremental cardiopulmonary exercise test and a constant speed treadmill session at 70% of maximal intensity for 6 minutes. The onset of the exercise (first 360 seconds) response for O(2) uptake and HR was modeled according to a monoexponential fit.

RESULTS

Oxygen consumption and HR on-kinetics were slower in the COPD group compared with controls. Additionally, VO(2) on-kinetic parameters revealed a strong positive correlation (r = 0.77, P < 0.05) with BODE scores and a moderate negative correlation with walking distance (r = -0.45, P < 0.05).

CONCLUSION

Our data show that moderate-to-severe COPD is related to impaired oxygen delivery and utilization during the onset of intense exercise.

Effects of a 6-month exercise program pilot study on walking economy, peak physiological characteristics, and walking performance in patients with peripheral arterial disease

The purpose of this study was to examine the effects of a 6-month exercise program on submaximal walking economy in individuals with peripheral arterial disease and intermittent claudication (PAD-IC). Participants (n = 16) were randomly allocated to either a control PAD-IC group (CPAD-IC, n = 6) which received standard medical therapy, or a treatment PAD-IC group (TPAD-IC; n = 10) which took part in a supervised exercise program. During a graded treadmill test, physiological responses, including oxygen consumption, were assessed to calculate walking economy during submaximal and maximal walking performance. Differences between groups at baseline and post-intervention were analyzed via Kruskal–Wallis tests. At baseline, CPAD-IC and TPAD-IC groups demonstrated similar walking performance and physiological responses. Postintervention, TPAD-IC patients demonstrated significantly lower oxygen consumption during the graded exercise test, and greater maximal walking performance compared to CPAD-IC. These preliminary results indicate that 6 months of regular exercise improves both submaximal walking economy and maximal walking performance, without significant changes in maximal walking economy. Enhanced walking economy may contribute to physiological efficiency, which in turn may improve walking performance as demonstrated by PAD-IC patients following regular exercise programs.

Exercise intensity and oxygen uptake kinetics in African-American and Caucasian women

The effect of exercise intensity on the on- and off-transient kinetics of oxygen uptake (VO(2)) was investigated in African American (AA) and Caucasian (C) women. African American (n = 7) and Caucasian (n = 6) women of similar age, body mass index and weight, performed an incremental test and bouts of square-wave exercise at moderate, heavy and very heavy intensities on a cycle ergometer. Gas exchange threshold (LT(GE)) was lower in AA (13.6 ± 2.3 mL kg(-1) min(-1)) than C (18.6 ± 5.6 mL kg(-1) min(-1)). The dynamic exercise and recovery VO(2) responses were characterized by mathematical models. There were no significant differences in (1) peak oxygen uptake (VO(2peak)) between AA (28.5 ± 5 mL kg(-1) min(-1)) and C (31.1 ± 6.6 mL kg(-1) min(-1)) and (2) VO(2) kinetics at any exercise intensity. At moderate exercise, the on- and off- VO(2) kinetics was described by a monoexponential function with similar time constants τ (1,on) (39.4 ± 12.5; 38.8 ± 15 s) and τ (1,off) (52.7 ± 10.1; 40.7 ± 4.4 s) for AA and C, respectively. At heavy and very heavy exercise, the VO(2) kinetics was described by a double-exponential function. The parameter values for heavy and very heavy exercise in the AA group were, respectively: τ (1,on) (47.0 ± 10.8; 44.3 ± 10 s), τ (2,on) (289 ± 63; 219 ± 90 s), τ (1,off) (45.9 ± 6.2; 50.7 ± 10 s), τ (2,off) (259 ± 120; 243 ± 93 s) while in the C group were, respectively: τ (1,on) (41 ± 12; 43.2 ± 15 s); τ (2, on) (277 ± 81; 215 ± 36 s), τ (1,off) (40.2 ± 3.4; 42.3 ± 7.2 s), τ (2,off) (215 ± 133; 228 ± 64 s). The on- and off-transients were symmetrical with respect to model order and dependent on exercise intensity regardless of race. Despite similar VO(2) kinetics, LT(GE) and gain of the VO(2) on-kinetics at moderate intensity were lower in AA than C. However, generalization to the African American and Caucasian populations is constrained by the small subject numbers.

Relação entre aptidão física e os indicadores de qualidade de vida de indivíduos com claudicação intermitente

O objetivo deste estudo foi verificar a relação entre a aptidão física e os indicadores de qualidade de vida de indivíduos com claudicação intermitente (CI). Participaram do estudo 42 indivíduos (65,2 ± 8,3 anos) com CI, de ambos os gêneros. Para a avaliação da aptidão física, foram realizados teste de esforço em esteira, para obtenção da distância de claudicação (DC) e da distância total de marcha (DTM) e o teste de uma repetição máxima no exercício extensão de joelho. Os indicadores de qualidade de vida foram avaliados por meio do Medical Outcome Study Questionnaire Short Form 36, composto por oito domínios: capacidade funcional (CF), aspectos físicos (AF), dor, estado geral de saúde, vitalidade (VI), aspectos sociais (AS), aspectos emocionais (AE) e saúde mental. Para a análise estatística foi utilizado o coeficiente de correlação de Pearson, com p < 0,05. Foi observada correlação significante entre o domínio da CF com a DC e a DTM (r = 0,60, p < 0,01 e r = 0,49, p < 0,01, respectivamente), o domínio da AF com a DTM (r = 0,46, p < 0,01), o domínio da VI e dos AS com a DC (r = 0,34, p = 0,03 e r = 0,33, p = 0,04, respectivamente) e o domínio da AE com a DC e a DTM (r = 0,43, p = 0,01 e r = 0,44, p = 0,01, respectivamente). Como conclusão, os resultados deste estudo sugerem que os indicadores da qualidade de vida nos domínios da saúde física e da saúde emocional são relacionados com a capacidade de caminhada de indivíduos com CI

Relationship between leg muscle capillary density and peak hyperemic blood flow with endurance capacity in peripheral artery disease

The aim of this study was to determine if skeletal muscle capillary density is lower in patients with peripheral artery disease (PAD) and if capillary density relates to functional limitations. PAD patients with intermittent claudication (IC) have a decreased exercise tolerance due to exercise-induced muscle ischemia. Despite the apparent role diminished arterial flow has in this population, the degree of walking pain and functional limitation is not entirely explained by altered hemodynamics of the affected limbs. We hypothesized that skeletal muscle capillary density is lower in PAD and is related to the functional impairment observed in this population. Sixty-four patients with PAD and 56 controls underwent cardiopulmonary exercise testing and a gastrocnemius muscle biopsy. A subset of these patients (48 PAD and 47 controls) underwent peak hyperemic flow testing via plethysmography. Capillary density in PAD patients was lower compared with controls (P < 0.001). After adjustment for several baseline demographic imbalances the model relating capillary density to peak oxygen consumption (Vo(2)) remained significant (P < 0.001). In PAD subjects, capillary density correlated with peak Vo(2), peak walking time (PWT), and claudication onset time (COT). Peak hyperemic blood flow related to peak Vo(2) in both PAD and control subjects. PAD is associated with lower capillary density, and capillary density is related to the functional impairment as defined by a reduced peak Vo(2), PWT, and COT. These findings suggest that alterations in microcirculation may contribute to functional impairment capacity in PAD.

Hemoglobin and myoglobin contributions to skeletal muscle oxygenation in response to exercise

The quantitative contributions of hemoglobin and myoglobin oxygenation in skeletal muscle depend on physiological factors, especially muscle blood flow (Q( m )) and capillary permeability-surface area (PS). Near-infrared spectroscopy (NIRS) can be used to quantify total heme oxidation, but it is unable to distinguish between hemoglobin and myoglobin. Therefore, a mechanistic computational model has been developed to distinguish the contributions of oxygenated hemoglobin and myoglobin to the total NIRS signal. Model simulations predict how Q( m ) and PS can affect oxygenated hemoglobin and myoglobin.Although both hemoglobin and myoglobin oxygenation decrease with impaired Q( m ), simulations show that myoglobin provides a greater contribution to the overall NIRS signal. A decrease of PS primarily affects myoglobin oxygenation. Based on model simulations, the contribution of myoglobin oxygenation to the total NIRS signal can be significantly different under pathophysiological conditions, such as diabetes and peripheral arterial disorder.

Plantar flexion: an effective training for peripheral arterial disease

This study examined whether a training intervention likely to elicit adaptations in the leg could result in reduced leg pain and increased whole body physical capacity. Twenty-seven peripheral arterial disease (PAD) patients were randomized to either an individual leg plantar flexion training group (TG) training 4 x 4 min intervals at 80% of maximal work rate three times per week for 8 weeks or a control group. The TG significantly increased plantar flexion peak oxygen uptake and power output by 23.5 and 43.9%, respectively. Treadmill peak oxygen uptake (VO(2peak)) significantly increased 12.3% in the TG and was associated with a significant increased time to exhaustion of 20.0% when treadmill walking. Eleven of 14 patients no longer reported leg pain limitations at VO(2peak). No differences in cardiac output measured at VO(2peak), or walking economy were observed. Plantar flexion training was effective in increasing VO(2peak) and walking performance, and may be a useful strategy in treatment of PAD.

The myopathy of peripheral arterial occlusive disease: part 1. Functional and histomorphological changes and evidence for mitochondrial dysfunction

In recent years, an increasing number of studies have demonstrated that a myopathy is present, contributes, and, to a certain extent, determines the pathogenesis of peripheral arterial occlusive disease (PAD). These works provide evidence that a state of repetitive cycles of exercise-induced ischemia followed by reperfusion at rest operates in PAD patients and mediates a large number of structural and metabolic changes in the muscle, resulting in reduced strength and function. The key players in this process appear to be defective mitochondria that, through multilevel failure in their roles as energy, oxygen radical species, and apoptosis regulators, produce and sustain a progressive decline in muscle performance. In this 2-part review, we highlight the currently available evidence that characterizes the nature and mechanisms responsible for this myopathy. In part 1, the authors review the functional and histomorphological characteristics of the myopathy and focus on the biochemistry and bioenergetics of its mitochondriopathy. In part 2, they then review accumulating evidence that oxidative stress related to ischemia reperfusion is probably the major operating mechanism of PAD myopathy. Important new findings of a possible neuropathy and a shift in muscle fiber type are also reviewed. Learning more about these mechanisms will enhance our understanding of the degree to which they are preventable and treatable.

Relationship between temporal-spatial gait parameters, gait kinematics, walking performance, exercise capacity, and physical activity level in peripheral arterial disease

OBJECTIVE

Impaired physical function is a feature of patients with peripheral arterial disease (PAD) who present with symptoms of intermittent claudication (PAD-IC). Previous research found that temporal-spatial gait parameters do not discriminate between PAD-IC patients and control subjects during normal and maximal walking even though PAD-IC patients have decreased physical function characteristic of the disease. This study examined the hypothesis that patients with PAD-IC would demonstrate decreased temporal-spatial gait parameters, gait kinematics, walking performance, physiologic responses to exercise, and physical activity level compared with control subjects. The aim was to examine the temporal-spatial gait parameters and gait kinematics of individuals with PAD-IC and to determine the relationship between these variables and walking performance, exercise capacity, and physical activity level in these individuals.

METHOD

A cross-sectional study of 28 PAD-IC subjects (IC) and 25 controls (CON) matched for age and mass was conducted in a medical faculty human performance laboratory. IC subjects had a history of PAD, ankle-brachial pressure index (ABI)<0.9 in at least one leg, and a positive Edinburgh Claudication Questionnaire response. Gait characteristics were determined by two-dimensional motion analysis. A graded treadmill test was used to assess walking performance and peak physiologic responses to exercise. Physical activity levels were measured by analysis of 7-day pedometer recording motion. Differences between groups were examined by one-way analysis of covariance.

RESULTS

Compared with CON, IC temporal-spatial gait parameters were significantly lower (P<.05), except for single support ipsilateral limb time. IC subjects spent a greater percentage of time in gait support phases, took longer to complete a stride, and had reduced stride length and walking speeds during the gait cycle. IC joint angular kinematics showed significantly reduced displacement of ankle plantar flexion (P=.017), knee range of motion (P=.021), and hip extension (P=.016) compared with the CON subjects during the gait cycle. All joint minimum and maximum angular velocities and accelerations, walking physiologic responses, and physical activity levels were significantly lower for IC compared with the CON subjects.

CONCLUSION

IC subjects walk with a shuffling gait pattern indicated by reduced joint angular displacement, velocities, and accelerations that results in reduced walking performance and physiologic responses and physical activity compared with controls matched for age, mass, and physical activity.

A comparison of treadmill and arm-leg ergometry exercise testing for assessing exercise capacity in patients with peripheral arterial disease

PURPOSE

To compare the results of treadmill exercise testing (TM) to arm-leg ergometry testing (AL) in patients with peripheral arterial disease (PAD).

METHODS

Twelve men and 8 women with PAD (mean age, 62 +/- 10 years) completed a treadmill test and an arm-leg ergometer exercise test. Oxygen uptake, heart rate, rate-pressure product (x10(-3)), ratings of claudication and perceived exertion, and power were measured.

RESULTS

Peak oxygen uptake, heart rate, and rate-pressure product were similar between TM and AL. Exercise duration was longer and the peak power higher on the AL than on the TM. Claudication pain > or =3/4 was the reason for test termination in all subjects during TM test and in 13 subjects during AL. Nine patients discontinued due to severe claudication on both tests, but the pain occurred later in AL than TM.

CONCLUSIONS

Although peak oxygen uptake was similar between the 2 exercise tests, patients with PAD exercised longer and to a higher peak power during the AL. These data suggest that the AL test may be used to evaluate peak exercise capacity in patients with PAD. The AL may also provide an alternate method for detecting PAD and coronary heart disease.

Skeletal muscle StO2 kinetics are slowed during low work rate calf exercise in peripheral arterial disease

The time course of muscle oxygen desaturation (StO2 kinetics) following exercise onset reflects the dynamic interaction between muscle blood flow and muscle oxygen consumption. In patients with peripheral arterial disease (PAD), muscle StO2 kinetics are slowed during walking exercise; potentially reflecting altered muscle oxygen consumption relative to blood flow. This study evaluated whether StO2 kinetics measured using near infrared spectroscopy (NIRS) would be slowed in PAD during low work rate calf exercise compared with healthy subjects under conditions in which blood flow did not differ. Eight subjects with PAD and eight controls performed 3 min of calf exercise at 5, 10, 30, and 50% of maximal voluntary contraction (MVC). Calf blood flow responses were measured by plethysmography. Power outputs were similar between groups for all work rates. In PAD, the time constants of StO2 kinetics were significantly slower than controls during 5% MVC (13.5 +/- 1.7 vs. 6.9 +/- 1.2 s, P < 0.05) and 10% MVC work rates (14.5 +/- 2.7 vs. 6.8 +/- 1.1 s, P < 0.05). Blood flow assessed when exercise was interrupted after 30 s did not differ between PAD and control subjects at these work rates. In contrast, the StO2 time constants were not different between groups during 30 and 50% MVC work rates, where blood flow responses in PAD subjects were lower as compared with controls. Thus in PAD, the slowed StO2 kinetic responses under conditions of unimpaired calf blood flow reflect slowed muscle oxygen consumption in PAD skeletal muscle during low work rate plantar flexion exercise as compared with healthy skeletal muscle.

Relative Tolerance to Upper- and Lower-Limb Aerobic Exercise in Patients with Peripheral Arterial Disease

OBJECTIVES

To investigate the effects of peripheral arterial disease (PAD) on relative tolerance to upper- and lower-limb aerobic exercise.

METHODS

Peak cardiorespiratory responses evoked by an incremental arm-cranking test (ACT) and an incremental leg-cranking test (LCT) were compared in patients with PAD (N=101; median age 69 year, range 50-85 years). Claudication distance (CD) and total distance before intolerable claudication pain (maximum walking distance: MWD) were also assessed during walking.

RESULTS

Peak oxygen consumption (V O(2)) for the ACT was 94% of that measured for the LCT (1.01+/-0.03 versus 1.10+/-0.03lmin(-1), respectively; P<0.001), but in a significant proportion of patients (35%; P<0.001), exceeded that recorded for the LCT. The ratio of upper- to lower-limb peak V O(2) was higher (0.98+/-0.04 compared to 0.98+/-0.05lmin(-1) and 1.00+/-0.06 compared to 1.21+/-0.06lmin(-1); P<0.01), whereas walking performance (CD: 94+/-14 versus 187+/-25 m, P<0.01; MWD: 227+/-20 versus 394+/-33 m, P<0.01) was lower for patients in the lowest ankle to brachial pressure index quartile compared to patients in the highest quartile, respectively.

CONCLUSION

Upper-limb aerobic conditioning could be a useful exercise stimulus for maintaining or improving cardiorespiratory function in patients with severe PAD as they have a greater relative upper-limb aerobic power.

Impaired muscle oxygen use at onset of exercise in peripheral arterial disease

OBJECTIVES

In patients with peripheral arterial disease (PAD), abnormal muscle metabolism and impaired oxygen delivery distal to the arterial occlusions may contribute to the exercise limitation observed in this population. Muscle tissue hemoglobin saturation (StO2), measured with near-infrared spectroscopy, reflects the relative contributions of oxygen delivery and oxygen use. Thus differences in the kinetics of StO2 in response to exercise may yield important insight into the potential mechanisms associated with the PAD exercise impairment. The purposes of this study were to characterize the muscle oxygenation responses in patients with PAD and in healthy control subjects at the onset of exercise, and to compare the kinetics of StO2 desaturation. We hypothesized that at the onset of exercise the kinetics of StO2 desaturation would be slowed in PAD compared with control responses.

MATERIAL AND METHODS

Six patients with PAD and 6 healthy control subjects from a university center were examined in a prospective cross-sectional analysis that evaluated the desaturation kinetics of StO2 at the onset of walking exercise. On separate visits subjects performed graded treadmill exercise and 3 constant work rate treadmill tests equivalent to approximately 60% (low), approximately 80% (medium), and 100% (peak) of their peak exercise work rate. Gastrocnemious muscle StO2 response profiles (InSpectra tissue spectrometer) were measured at rest and across the rest to exercise transition. Muscle StO2 responses were characterized by an exponential mathematical model. The end point value was taken as the time constant of StO2 desaturation after onset of exercise (ie, equivalent to time to reach approximately 63% of StO2 decrease).

RESULTS

The patients with PAD and the control subjects were of similar age and activity level. The qualitative patterns of StO2 responses at onset of exercise were also similar between patients and control subjects at all work rates. However, the kinetic time constants of StO2 desaturation were prolonged in patients with PAD versus control subjects (averaged time constant across all work rates, 21.9 +/- 9.4 seconds vs 4.9 +/- 2.2 seconds; P <.01).

CONCLUSIONS

The slowed muscle StO2 kinetics in PAD are consistent with an impairment in muscle oxygen use at the onset of walking exercise. Impaired muscle metabolism may contribute to the altered physiologic responses to exercise and to exercise impairment in patients with PAD.