Pré-condicionamento isquêmico remoto em portadores de claudicação intermitente de membros inferiores

INTRODUÇÃO: Pré-condicionamento isquêmico remoto (PCIR) é o fenômeno pelo qual curtos períodos de isquemia sub-letal sobre um órgão ou tecido, intercalados com reperfusão do mesmo, conferem a outros órgãos ou tecidos distantes deste, um aumento na capacidade da resistir a episódios subsequentes de isquemia, a qual os mesmos possam ser expostos. Com base nesse fato, testamos a hipótese de que o pré-condicionamento isquêmico remoto em pacientes portadores de claudicação intermitente de membros inferiores poderia aumentar a capacidade de deambulação desses pacientes, extrapolando o conceito do PCIR de aumento da capacidade de preservação da integridade celular frente à isquemia, para a manutenção da função celular, tornando a célula mais apta ao trabalho em situações de privação de oxigênio, geradas pela restrição do fluxo sanguíneo, como ocorre nos pacientes com claudicação intermitente de membros inferiores, durante o exercício. OBJETIVOS: Avaliar se o PCIR aumenta a distância de início de claudicação e/ou a distância total de claudicação em pacientes com doença arterial obstrutiva periférica. MÉTODOS: Foram estudados 52 pacientes ambulatoriais que apresentavam queixa de claudicação intermitente dos membros inferiores, associada a um pulso arterial ausente ou reduzido no membro sintomático e/ou um índice tornozelo-braço <0,90. Estes pacientes foram randomizados em três grupos (A, B e C). Todos os pacientes foram submetidos a dois testes de caminhada em esteira de acordo com o protocolo de Gardner. O grupo A fez o primeiro teste de esteira sem o pré-condicionamento isquêmico remoto e, após 7 dias, foi submetido a um novo teste de esteira, agora precedido pelo pré-condicionamento isquêmico remoto. O grupo B foi submetido ao pré-condicionamento isquêmico remoto antes do primeiro teste de esteira e, após 7 dias, realizou novo teste de esteira, agora sem o pré-condicionamento isquêmico remoto. Já no Grupo C (grupo controle), ambos os testes de esteira foram realizados sem pré-condicionamento isquêmico remoto, também com 7 dias de intervalo. RESULTADOS: Os grupos A e C mostraram um aumento na distância de início de claudicação, no segundo teste, em comparação com o primeiro teste. O grupo A teve um aumento estatisticamente significativo, em relação ao grupo C (grupo controle). Com relação à distância total de claudicação, todos os grupos (A, B e C), mostraram um aumento estatisticamente significativo a favor do segundo teste, porém não foi observada diferença entre os grupos (A, B e C). CONCLUSÕES: O pré-condicionamento isquêmico remoto aumentou a distância inicial de claudicação em pacientes com claudicação intermitente, no entanto, ele não afetou a distância total de claudicação dos pacientes portadores de claudicação intermitente de membros inferiores

Effect of carbohydrate supplementation on walking performance in peripheral arterial disease: A preliminary physiologic study

Objective: In this preliminary study we tested the effect of short-term carbohydrate supplementation on carbohydrate oxidation and walking performance in peripheral arterial disease. Methods: Eleven patients with peripheral arterial disease and intermittent claudication and 8 healthy control subjects completed several weeks of baseline exercise testing, then were given supplementation for 3 days with a carbohydrate solution and placebo. Maximal walking time was assessed with a graded treadmill test. Carbohydrate oxidation during a submaximal phase of this test was measured with indirect calorimetry. At the end of baseline testing a biopsy specimen was taken from the gastrocnemius muscle, and the active fraction of pyruvate dehydrogenase complex activity was determined. Results: Carbohydrate supplementation resulted in a significant increase in body weight and carbohydrate oxidation during exercise in patients with intermittent claudication and control subjects. Maximal walking time decreased by 3% in control subjects, whereas it increased by 6% in patients with intermittent claudication (group X treatment interaction, P < .05). There was a wide range of performance responses to carbohydrate supplementation among patients with claudication (-3%-37%). This effect was greater in poorer performers, and was negatively correlated (P < .05) with muscle pyruvate dehydrogenase complex activity. Conclusion: Preliminary data suggest that carbohydrate oxidation during exercise might contribute to exercise intolerance in more dysfunctional patients with intermittent claudication and that carbohydrate supplementation might be an effective therapeutic intervention in these patients.

Walking performance, oxygen uptake kinetics and resting muscle pyruvate dehydrogenase complex activity in peripheral arterial disease

In the present study, we tested the hypothesis that walking intolerance in intermittent claudication (IC) is related to both slowed whole body oxygen uptake (Vo(2)) kinetics and altered activity of the active fraction of the pyruvate dehydrogenase complex (PDCa) in skeletal muscle. Ten patients with IC and peripheral arterial disease [ankle/brachial index (ABI) = 0.73 +/- 0.13] and eight healthy controls (ABI = 1. 17 +/- 0.13) completed three maximal walking tests. From these tests, averaged estimates of walking time, peak Vo(2) and the time constant of Vo(2) (tau) during submaximal walking were obtained. A muscle sample was taken from the gastrocnemius medialis muscle at rest and analysed for PDCa and several other biochemical variables. Walking time and peak Vo(2) were approx. 50 % lower in patients with IC than controls, and tau was 2-fold higher (P < 0.05). r was significantly correlated with walking time (r = -0.72) and peak Vo(2) (r = -0.66) in patients with IC, but not in controls. PDCa was not significantly lower in patients with IC than controls; however, PDCa tended to be correlated with tau (r = -0.56, P = 0.09) in patients with IC, but not in controls (r = -0.14). A similar correlation was observed between resting ABI and tau (r = -0.63, P = 0.05) in patients with IC. These data suggest that the impaired Vo(2) kinetics contributes to walking intolerance in IC and that, within a group of patients with IC, differences in Vo(2) kinetics might be partly linked to differences in muscle carbohydrate oxidation.

Optimising exercise training in peripheral arterial disease

Peripheral arterial disease (PAD) is an obstructive condition where the flow of blood through peripheral arteries is impeded. During periods of increased oxygen demand (e.g. during exercise), peripheral limb ischaemia occurs, resulting in the sensation of muscle pain termed 'claudication'. As a result of claudication, subjects' ability to exercise is greatly reduced affecting their quality of life. Although many treatment options for patients with PAD exist, exercise training is an effective and low-cost means of improving functional ability and quality of life. Currently, there are limited specific recommendations to assist the exercise prescription and programming of these individuals. This review summarises data from 28 exercise training studies conducted in patients with PAD and formulates recommendations based on their results. Exercise training for patients with PAD should involve three training sessions per week comprising 45 minutes of intermittent treadmill walking in a supervised environment for a time period of 20 weeks or more. Encouragement and direction is given to further research aimed at investigating the effectiveness of training programmes in these patients.

Short-term effects of cycle and treadmill training on exercise tolerance in peripheral arterial disease

Background. To explore the efficacy of cycle training in the treatment of intermittent claudication, the present study compared performance and physiologic effects of cycle training with more conventional treadmill walking training in a group of patients with claudication. Method: Forty-two individuals with peripheral arterial disease and intermittent claudication (24 men, 18 women) were stratified by gender and the presence or absence of type 2 diabetes mellitus and then randomized to a treadmill (n = 13), cycle (n = 15), or control group (n = 14). Treadmill and cycle groups trained three times a week for 6 weeks, whereas the control group did not train during this period. Maximal and pain-free exercise times were measured on graded treadmill and cycle tests before and after training. Results. Treadmill training significantly improved maximal and pain-free treadmill walking times but did not improve cycle performance. Cycle training significantly improved maximal cycle time but did not improve treadmill performance. However, there was evidence of a stronger cross-transfer effect between the training modes for patients who reported a common limiting symptom during cycling and walking at baseline. There was also considerable variation in the training response to cycling, and a subgroup of responsive patients in the cycle group improved their walking performance by more than the average response observed in the treadmill group. Conclusion: These findings suggest that cycle exercise is not effective in improving walking performance in all claudication patients but might be an effective alternative to walking in those who exhibit similar limiting symptoms during both types of exercise.

Effect of training on the response of plasma vascular endothelial growth factor to exercise in patients with peripheral arterial disease

Expansion of the capillary network, or angiogenesis, occurs following endurance training. This process, which is reliant on the presence of VEGF (vascular endothelial growth factor), is an adaptation to a chronic mismatch between oxygen demand and supply. Patients with IC (intermittent claudication) experience pain during exercise associated with an inadequate oxygen delivery to the muscles. Therefore the aims of the present study were to examine the plasma VEGF response to acute exercise, and to establish whether exercise training alters this response in patients with IC. In Part A, blood was collected from patients with IC (n = 18) before and after (+ 20 and + 60 min post-exercise) a maximal walking test to determine the plasma VEGF response to acute exercise. VEGF was present in the plasma of patients (45.11 +/- 29.96 pg/ml) and was unchanged in response to acute exercise. Part B was a training study to determine whether exercise training altered the VEGF response to acute exercise. Patients were randomly assigned to a treatment group (TMT; n = 7) that completed 6 weeks of high-intensity treadmill training, or to a control group (CON; n = 6). All patients completed a maximal walking test before and after the intervention, with blood samples drawn as for Part A. Training had no effect on plasma VEGF at rest or in response to acute exercise, despite a significant increase in maximal walking time in the TMT group (915 + 533 to 1206 + 500 s; P = 0.009) following the intervention. The absence of a change in plasma VEGF may reflect altered VEGF binding at the endothelium, although this cannot be confirmed by the present data.

Intermittent access to 20% ethanol induces high ethanol consumption in Long-Evans and Wistar rats

BACKGROUND: There has been some difficulty getting standard laboratory rats to voluntarily consume large amounts of ethanol without the use of initiation procedures. It has previously been shown that standard laboratory rats will voluntarily consume high levels of ethanol if given intermittent-access to 20% ethanol in a 2-bottle-choice setting [Wise, Psychopharmacologia 29 (1973), 203]. In this study, we have further characterized this drinking model. METHODS: Ethanol-naïve Long-Evans rats were given intermittent-access to 20% ethanol (three 24-hour sessions per week). No sucrose fading was needed and water was always available ad libitum. Ethanol consumption, preference, and long-term drinking behaviors were investigated. Furthermore, to pharmacologically validate the intermittent-access 20% ethanol drinking paradigm, the efficacy of acamprosate and naltrexone in decreasing ethanol consumption were compared with those of groups given continuous-access to 10 or 20% ethanol, respectively. Additionally, ethanol consumption was investigated in Wistar and out-bred alcohol preferring (P) rats following intermittent-access to 20% ethanol. RESULTS: The intermittent-access 20% ethanol 2-bottle-choice drinking paradigm led standard laboratory rats to escalate their ethanol intake over the first 5 to 6 drinking sessions, reaching stable baseline consumption of high amounts of ethanol (Long-Evans: 5.1 +/- 0.6; Wistar: 5.8 +/- 0.8 g/kg/24 h, respectively). Furthermore, the cycles of excessive drinking and abstinence led to an increase in ethanol preference and increased efficacy of both acamprosate and naltrexone in Long-Evans rats. P-rats initiate drinking at a higher level than both Long-Evans and Wistar rats using the intermittent-access 20% ethanol paradigm and showed a trend toward a further escalation in ethanol intake over time (mean ethanol intake: 6.3 +/- 0.8 g/kg/24 h). CONCLUSION: Standard laboratory rats will voluntarily consume ethanol using the intermittent-access 20% ethanol drinking paradigm without the use of any initiation procedures. This model promises to be a valuable tool in the alcohol research field.

Intermittent drying of food products : a critical review

Drying is very energy intensive process and consumes about 20-25% of the energy used by food processing industry. The energy efficiency of the process and quality of dried product are two key factors in food drying. Global energy crisis and demand for quality dried food further challenge researchers to explore innovative techniques in food drying to address these issues. Intermittent drying is considered one of the promising solutions for improving energy efficiency and product quality without increasing the capital cost of the drier. Intermittent drying has already received much attention. However, a comprehensive review of recent progresses and overall assessment of energy efficiency and product quality in intermittent drying is lacking. The objective of this article is to discuss, analyze and evaluate the recent advances in intermittent drying research with energy efficiency and product quality as standpoint. Current available modelling techniques for intermittent drying are reviewed and their merits and demerits are analyzed. Moreover, intermittent application of ultrasound, infrared (IR) and microwave in combined drying technology have been reviewed and discussed. In this review article the gaps in the current literature are highlighted, some important future scopes for theoretical and experimental studies are identified and the direction of further research is suggested.

Bicep femoris voluntary activation deficits contribute to eccentric knee flexor weakness following intermittent running

INTRODUCTION: Hamstring strain injuries (HSI) are the predominant non-contact injury in many sports. Eccentric hamstring muscle weakness following intermittent running has been implicated within the aetiology of HSI. This weakness following intermittent running is often greater eccentrically than concentrically, however the cause of this unique, contraction mode specific phenomenon is unknown. AIM: To determine if this preferential eccentric decline in strength is caused by declines in voluntary hamstring muscle activation. METHODS: Fifteen recreationally active males completed 18 × 20m overground sprints. Maximal strength (concentric and eccentric knee flexor and concentric knee extensor) was determined isokinetically at the velocities of ±1800.s-1 and ±600.s- while hamstring muscle activation was assessed using surface electromyography, before and 15 minutes after the running protocol. RESULTS: Overground intermittent running caused greater eccentric (27.2 Nm; 95% CI = 11.2 to 43.3; p=0.0001) than concentric knee flexor weakness (9.3 Nm; 95% CI = -6.7 to 25.3; P=0.6361). Following the overground running, voluntary activation levels of the lateral hamstrings showed a significant decline (0.08%; 95% CI = 0.045 to 0.120; P<0.0001). In comparison, medial hamstring activation showed no change following intermittent running. CONCLUSION: Eccentric hamstring strength is decreased significantly following intermittent overground running. Voluntary activation deficits in the biceps femoris muscle are responsible for some portion of this weakness. The implications of this finding are significant because the biceps femoris muscle is the most frequently strained of all the hamstring muscles and because fatigue appears to play an important part in injury occurrence.

Do voluntary activation deficits contribute to eccentric weakness following intermittent running?

Hamstring strain injuries (HSI) are the predominant non-contact injury in many sports. Eccentric hamstring muscle weakness following intermittent running has been implicated within the aetiology of HSI. This weakness following intermittent running is often greater eccentrically than concentrically, however the cause of this unique, contraction mode specific phenomenon is unknown. PURPOSE: To determine if this preferential eccentric decline in strength is caused by declines in voluntary hamstring muscle activation. METHODS: Fifteen recreationally active males completed 18 × 20m overground sprints. Maximal strength (concentric and eccentric knee flexor and concentric knee extensor) was determined isokinetically at the velocities of ±1800.s-1 and ±600.s- while hamstring muscle activation was assessed using surface electromyography, before and 15 minutes after the running protocol. RESULTS: Overground intermittent running caused greater eccentric (27.2 Nm; 95% CI = 11.2 to 43.3; p=0.0001) than concentric knee flexor weakness (9.3 Nm; 95% CI = -6.7 to 25.3; P=0.6361). Following the overground running, voluntary activation levels of the lateral hamstrings showed a significant decline (0.08%; 95% CI = 0.045 to 0.120; P<0.0001). In comparison, medial hamstring activation showed an increased level of activation following intermittent running (0.12%; 95% CI = 0.049 to 0.030; P = 0.0102). CONCLUSION: Eccentric hamstring strength is decreased significantly following intermittent overground running. Voluntary activation deficits in the biceps femoris muscle are responsible for some portion of this weakness. The implications of this finding are significant because the biceps femoris muscle is the most frequently strained of all the hamstring muscles and because fatigue appears to play an important part in injury occurrence.

Volume-dependent response of precooling for intermittent-sprint exercise in the heat

Purpose: To assess the effects of pre-cooling volume on neuromuscular function and performance in free-paced intermittent-sprint exercise in the heat. Methods: Ten male, teamsport athletes completed four randomized trials involving an 85-min free-paced intermittentsprint exercise protocol in 33°C±33% relative humidity. Pre-cooling sessions included whole body (WB), head+hand (HH), head (H) and no cooling (CONT), applied for 20-min pre-exercise and 5-min mid exercise. Maximal voluntary contractions (MVC) were assessed pre- and postintervention and mid- and post-exercise. Exercise performance was assessed with sprint times, % decline and distances covered during free-paced bouts. Measures of core(Tc) and skin (Tsk) temperatures, heart rate, perceptual exertion and thermal stress were monitored throughout. Venous and capillary blood was analyzed for metabolite, muscle damage and inflammatory markers. Results: WB pre-cooling facilitated the maintenance of sprint times during the exercise protocol with reduced % decline (P=0.04). Mean and total hard running distances increased with pre cooling 12% compared to CONT (P<0.05), specifically, WB was 6-7% greater than HH (P=0.02) and H (P=0.001) respectively. No change was evident in mean voluntary or evoked force pre- to post-exercise with WB and HH cooling (P>0.05). WB and HH cooling reduced Tc by 0.1-0.3°C compared to other conditions (P<0.05). WB Tsk was suppressed for the entire session(P=0.001). HR responses following WB cooling were reduced(P=0.05; d=1.07) compared to CONT conditions during exercise. Conclusion: A relationship between pre-cooling volume and exercise performance seems apparent, as larger surface area coverage augmented subsequent free-paced exercise capacity, in conjunction with greater suppression of physiological load. Maintenance of MVC with pre-cooling, despite increased work output suggests the role of centrally-mediated mechanisms in exercise pacing regulation and subsequent performance.

Duration-dependant response of mixed-method pre-cooling for intermittent-sprint exercise in the heat

This study examined the effects of pre-cooling duration on performance and neuromuscular function for self-paced intermittent-sprint shuttle running in the heat. Eight male, team-sport athletes completed two 35-min bouts of intermittent-sprint shuttle running separated by a 15-min recovery on three separate occasions (33°C, 34% relative humidity). Mixed-method pre-cooling was completed for 20 min (COOL20), 10-min (COOL10) or no cooling (CONT) and reapplied for 5-min mid-exercise. Performance was assessed via sprint times, percentage decline and shuttle-running distance covered. Maximal voluntary contractions (MVC), voluntary activation (VA) and evoked twitch properties were recorded pre- and post-intervention and mid- and post-exercise. Core temperature (T c), skin temperature, heart rate, capillary blood metabolites, sweat losses, perceptual exertion and thermal stress were monitored throughout. Venous blood draws pre- and post-exercise were analyzed for muscle damage and inflammation markers. Shuttle-running distances covered were increased 5.2 ± 3.3% following COOL20 (P < 0.05), with no differences observed between COOL10 and CONT (P > 0.05). COOL20 aided in the maintenance of mid- and post-exercise MVC (P < 0.05; d > 0.80), despite no conditional differences in VA (P > 0.05). Pre-exercise T c was reduced by 0.15 ± 0.13°C with COOL20 (P < 0.05; d > 1.10), and remained lower throughout both COOL20 and COOL10 compared to CONT (P < 0.05; d > 0.80). Pre-cooling reduced sweat losses by 0.4 ± 0.3 kg (P < 0.02; d > 1.15), with COOL20 0.2 ± 0.4 kg less than COOL10 (P = 0.19; d = 1.01). Increased pre-cooling duration lowered physiological demands during exercise heat stress and facilitated the maintenance of self-paced intermittent-sprint performance in the heat. Importantly, the dose-response interaction of pre-cooling and sustained neuromuscular responses may explain the improved exercise performance in hot conditions.

Cold-water immersion decreases cerebral oxygenation but improves recovery after intermittent-sprint exercise in the heat

This study examined the effects of post-exercise cooling on recovery of neuromuscular, physiological, and cerebral hemodynamic responses after intermittent-sprint exercise in the heat. Nine participants underwent three post-exercise recovery trials, including a control (CONT), mixed-method cooling (MIX), and cold-water immersion (10 °C; CWI). Voluntary force and activation were assessed simultaneously with cerebral oxygenation (near-infrared spectroscopy) pre- and post-exercise, post-intervention, and 1-h and 24-h post-exercise. Measures of heart rate, core temperature, skin temperature, muscle damage, and inflammation were also collected. Both cooling interventions reduced heart rate, core, and skin temperature post-intervention (P < 0.05). CWI hastened the recovery of voluntary force by 12.7 ± 11.7% (mean ± SD) and 16.3 ± 10.5% 1-h post-exercise compared to MIX and CONT, respectively (P < 0.01). Voluntary force remained elevated by 16.1 ± 20.5% 24-h post-exercise after CWI compared to CONT (P < 0.05). Central activation was increased post-intervention and 1-h post-exercise with CWI compared to CONT (P < 0.05), without differences between conditions 24-h post-exercise (P > 0.05). CWI reduced cerebral oxygenation compared to MIX and CONT post-intervention (P < 0.01). Furthermore, cooling interventions reduced cortisol 1-h post-exercise (P < 0.01), although only CWI blunted creatine kinase 24-h post-exercise compared to CONT (P < 0.05). Accordingly, improvements in neuromuscular recovery after post-exercise cooling appear to be disassociated with cerebral oxygenation, rather reflecting reductions in thermoregulatory demands to sustain force production.