Training and exercise treatment of PAD patients

Figure 1. Physical exercise in LEAD

Background

Lower extremity artery disease (LEAD) is an occlusive atherosclerotic disease that affects peripheral arteries, reducing the blood flow to the lower limbs. The prevalence of LEAD is high: globally, 202 million people are affected, including 40 million in Europe. Its prevalence is slightly higher in men than in women, particularly in the younger age groups, and it is more common in non-Hispanic blacks (7.8%) than in whites (4.4%) [1].

LEAD usually develops after the age of 50 years, with an exponential increase after the age of 65 years [1].

LEAD shares the major cardiovascular risk factors, with some differences in their relative importance. Tobacco use and diabetes mellitus are major contributors to LEAD [2].

In the early stages, LEAD is usually asymptomatic but, with its progression, intermittent claudication (IC) appears, with a progressive decrease in walking performance as LEAD severity increases [3]. IC affects the patient’s functional level as well as quality of life (QOL).

Reduced physical activity due to leg pain can lead the patients into a vicious circle of a sedentary lifestyle, which again increases the progression of the disease.

A structured or supervised physical activity programme can break this circle and dramatically improve QOL, functional capacity and cardiovascular outcome.

Effects of exercise

As ESC recent guidelines state, exercise therapy (ExT) is highly recommended and effective for improving symptoms, walking distance and QOL [4].

ExT can work through multiple paths, e.g., by increasing blood flow, improving endothelial function, providing long-term reduction in inflammation and oxidative stress, inducing angiogenesis or modifying muscle morphology and metabolism [5].

Despite the fact that the mechanisms are still debated, it is unanimously recognised that ExT can dramatically change the QOL of patients with IC.

However, ExT is still underused. A recent meta-analysis highlighted that ExT improves cardiorespiratory fitness, pain-free and total flat-ground walking distances, as well as graded treadmill performance in LEAD patients [6].

A Cochrane review found that ExT increased maximal walking time by almost five minutes compared with usual care [7]. Notably, supervised ExT seems superior to surgical treatment in improving treadmill walking performance, even for those with aortoiliac peripheral artery disease [8].

Therefore, the promotion of ExT in patients with LEAD/IC is the most important non-pharmacological strategy not only to treat and prevent the disease, but also for cardiovascular mortality and morbidity [9].

Functional assessment

Functional assessments allow an objective evaluation of the functional limitation in order to assess the stability of the clinical status, and to evaluate changes in performance after revascularisation, pharmacological treatment or rehabilitation intervention.

Constant load or ramp protocols are the most used protocols on the treadmill. Constant-load tests involve walking patients at a constant speed and slope (2.3 km/hr at 7.5%, 3.0 or 3.2 km/hr at 10%) until symptoms appear.

Ramp protocols involve a fixed walking speed (e.g., 3.2 or 3.5 km/hr) with increases in slope at predetermined time intervals (3.5% every 3 minutes or 2% every 2 minutes) until pain threshold is reached.

The key parameters obtained through these tests, useful for assessing walking performance, are absolute claudication distance (ACD), total walking distance (TWD), and maximal walking distance (MWD). These acronyms are used to indicate the total distance that the subject with LEAD is able to walk before the ischaemic pain becomes so severe that he/she must stop walking.

Absolute claudication time (ACT), maximal walking time (MWT), and peak walking time (PWT), on the other hand, refer to the maximum walking time the patient is able to manage before the ischaemic pain forces him/her to stop. 

Pain-free walking distance (PFWD), and intermittent claudication distance/initial claudication distance (ICD) represent the walking distance covered without ischaemic pain.

The severity of the symptoms experienced by the patient during the test can also be evaluated through a pain scale ranging from 0 to 4 (0 = no pain, 1 = onset of claudication, 2 = mild pain, 3 = moderate pain, 4 = severe pain).

One of the most known and diffuse protocols is the 6-minute walk test or six-minute walking test. This easy-to-perform test consists of patients walking the maximum possible distance in 6 minutes. Once claudication appears, the patient informs the physician by continuing to walk until the claudication becomes unbearable. Once walking is interrupted due to pain, the patient can resume the test as soon as possible. After the 6 minutes have elapsed, the total distance walked is calculated and the distance at the onset of symptoms (PFWD) is noted. In absolute terms, a walking distance of less than 300 m is considered an unfavourable prognostic value in terms of short-term cardiovascular morbidity and mortality. 

Type of exercise

Before exercise prescription, cardiovascular and injury risk should be assessed by the exercise physiologist or health professional prescribing exercise guided by a cardiologic framework (e.g., an electrocardiogram [ECG], cardiac imaging, and/or stress testing). Routine stress testing in asymptomatic patients is not required, as a low rate of complications (1 in 10,340 patients) has been described previously [10].

The cardiologist in conjunction with the physiotherapist or kinesiologist should have four main objectives for prescribing supervised exercise (SET):-

- Select the most appropriate exercise modalities (resistance training, strength training, combination training, etc.).

- Select the appropriate intensity of exercise.

- Educate the patient on what to expect from the exercise programme by providing a progression of training (with planned increases in intensity and duration over time).

- Have the subject understand the exercise routine and what to expect from it. Patients should be informed that it typically takes 4 to 6 weeks to realise improvements in walking performance.

Endurance training

Endurance training is set around endurance and is based on the ability to tolerate physical exertion for a certain period of time. Also called aerobic training, it includes activities that increase heart rate and respiratory rate. Examples include walking, swimming and cycling.

For those patients who can walk, interval walking at the maximum tolerable speed is the most frequently recommended exercise modality for this population. Three sessions per week, of at least 40 minutes of walking in each session, consistently lead to improvements in walking ability [6].

There should be warm-up and cool-down periods of 5-10 minutes each. The initial workload of the treadmill is set to a speed and grade that elicit claudication symptoms within 3-5 minutes; patients should walk at this pace until claudication of moderate severity occurs, then rest standing or sitting for a brief period to permit symptoms to subside. The exercise–rest–exercise pattern should be repeated throughout the exercise session. As the patient’s walking ability improves, the exercise workload should be increased by modifying the treadmill grade or speed (or both) to ensure that the stimulus for claudication pain always occurs during the workout. As walking ability improves, and a higher heart rate is reached, there is the possibility that cardiac signs and symptoms may appear. These symptoms should be appropriately diagnosed and treated [4].

For those patients who find it difficult to complete walking because of early or intolerable claudication pain, or other comorbidities, other forms of aerobic exercise such as lower extremity aerobic circuit training (which is a type of overload training performed in a circuit of multiple sets of exercises using medium to high repetitions, low intensities, with no breaks, or very short breaks between exercises, generally involving the calf, quadriceps, and hamstrings), and Nordic Pole walking (walking while using poles), have been shown to be effective in improving walking ability [11].

Strength training

Increasing strength and muscle mass, increasing connective tissue strength, and decreasing the risk of injury are the main benefits of this type of physical activity.

A minimum of two, ideally three, sessions per week, performed on non-consecutive days, is recommended.

Resistance training is usually prescribed in addition to walking or other forms of aerobic exercise, although it should be noted that the effects of this combined approach have not been systematically examined in PAD.

Patients should undertake 3 sets of 8-12 repetitions with rest intervals of 1-2 minutes of progressive whole-body resistance training incorporating 6-8 exercises including the primary muscle groups involved in walking (i.e., gastrocnemius, tibialis anterior, quadriceps, hamstrings, and glutes). If time is limited, the focus should be on strengthening the lower extremity muscles, as improvements in leg muscle function are often accompanied by improvements in walking ability in LEAD [12].

Exercise prescriptions for LEAD may consider arm cranking as well as lower limb exercise, possibly at short vigorous intensity intervals, but only to a threshold of mild pain [6].

Supervised, unsupervised and tele-exercise

Exercise programmes may be self-directed, supervised, and institution- or home-based.

Supervised exercise has been shown to reduce overall cardiovascular mortality by 52% and morbidity by 30% [9] and increase maximal walking distance more than unsupervised exercise in LEAD patients [7].

However, since not all patients can be involved in participation in supervised exercise programmes, alternative options should be offered. Home-based exercise did not show significant improvement in symptoms and walking ability, although data are still scarce: a 2015 review highlighted that home-based supervised exercise may improve maximal and PFWD compared to just giving advice about exercise, but it was less effective than hospital-based supervised exercise [14].

The recent LITE trial [15], a multicentre study with 305 LEAD patients, showed that high-intensity home-based exercise with telephone coaching meaningfully improved 6-minute walking distance; on the other hand, light-intensity home-based exercise and control did not improve walking performance.

These results underline how modern technology, such as tele-coaching or telemonitoring associated with wearable monitors and accelerators, could be an option for patients with LEAD to improve their quality of life and walking distance.

Conclusion

In LEAD, walking turns out to be the most diffuse and effective form of aerobic training, with an interval mode of exercise and setting its timing mainly on the subjective pain threshold based on the Borg scale. The studies analysed show that a period of exercise set around this type of training contributes effectively to an improvement in exercise performance and functional status of the subject suffering from LEAD.

In particular, there is an increase in timing and total distance during walking and a lengthening of the walking parameters and time travelled below the threshold of ischaemic pain.

Strength training involving multiple muscle groups, characterised by activity intervals and rest periods calculated from the Borg scale, maximum repetitions, or the onset of perceived ischaemic pain, may yield results similar to or less than endurance-based training at the level of subjects' walking performance.

Although many studies support exercise as a conservative treatment for LEAD, the idea of a surgical approach as the only way to improve symptoms, exercise performance, and quality of life for LEAD subjects remains deep-rooted.

If the goal is to offer best medical therapy to these patients, healthcare professionals must recommend and refer to structured, supervised exercise programmes, which must be made available both in community health services and in hospitals. In addition, new technology, telemedicine, coaching, and strategies for facilitating exercise in a home-based setting could be game changing if well structured.