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Training Guided By Pain Threshold Speed: Effects of a Home-Based Program on Claudication

Posted on: Thursday, 26 May 2005, 03:00 CDT

Aim. To verify the effectiveness of a 120 day home-based program guided by the pain threshold speed (PTS).

Methods. Twenty-nine patients with stable claudication were measured for ankle pressure (AP), ankle-brachial index (ABI), PTS, maximal speed (S^sub max^) on treadmill. Daily walking sessions at a speed 20-30% below PTS were prescribed. Determination of the training speed was supervised and facilitated at home. The program included a daily record of exercise data and symptoms, an intermediate PTS reevaluation to adjust the training speed, and the reassessment of all the parameters after 120 days.

Results. Overall patients showed a reduction of systemic blood pressure (151.314.3 to 147.618.3 mmHg; 77.1 9.1 to 72.48, p=0.008) while AP did not. ABI increased from 0.650.13 to 0.71 0.18 (p=0.01). PTS and S^sub max^ rose from 3.21.1 to 4.21.5 km/h (p=0.0001) and from 3.91.3 to 4.61.3 km/h (p=0.0001), respectively. According to their compliance, patients were divided into 3 groups: 1) trained (T, n=14): exercise at the prescribed speed, 2) free-walkers (FW, n=7): walking speed markedly below PTS and 3) untrained (U, n=8): incomplete program compliance. T group showed symptom reduction up to pain disappearance. The ABI change (0.720.09 to 0.82 0.16, p<0.02) was correlated to AP increase (r= 0.879). PTS and S^sub max^ rose from 3.61.1 to 5.40.8 km/h (p<0.02) and from 4.71.2 to 5.70.7 (p<0.02), respectively. FW showed improvement of all parameters, and U a better walking efficiency.

Conclusion. In patients with claudication, a low-cost home-based program driven by PTS allows dramatic improvements of functional parameters.

[Int Angiol 2004;23:379-87]

Key words: Claudication, peripheral vascular disease, exercise, rehabilitation, test.

Physical exercise represents an essential element in treating patients with second-stage peripheral arterial occlusive disease (PAOD).1 Exercise is effective in reducing risk factors 2 and, above all, in bringing about documented functional improvements, even though these are often unaccompanied by significant hemodynamic changes.1

Exercise training, which has been shown to be more effective if carried out at specialized centers,3 is currently based on repeated walking sessions performed at certain levels of pain that improve the exercise tolerance, thereby making possible progressively longer training sessions. However, the study of histological modifications in patients who undergo such types of training has demonstrated a lack of development of aerobic enzymes and an increase in anaerobic ones, together with signs of muscular damage.4 Research for new rehabilitation models is therefore warranted. A hypothetical objective to pursue could be an increase in the capacity to produce energy through aerobic mechanisms in the oxygen-deficient areas through induction of an increased muscle mitochondria concentration and capillarity. Such effects are attainable through specific exercise carried out for sufficiently long periods at submaximal intensities.5 A target intensity for exercise training could therefore be efficacious in PAOD patients, and could be used as the basis for developing appropriate methods for evaluation and rehabilitation training.

A first step in this direction was made with the setting up of tests, initially in a corridor 6 and more recently on a treadmill,7 aimed at determining the critical walking speed of the arteriopathic patient, the so-called pain threshold speed (PTS). This parameter could be useful for defining submaximal aerobic exercise and for evaluating the effects of such training. Beginning with these methodological presuppositions, this study examines the effectiveness of a PTS-guided rehabilitation program lasting 120 days. Compliance to home-based, submaximal exercise is also evaluated.

TABLE I.-General characteristics of the entire study population.

Materials and methods

Twenty-nine patients (19 males, 10 females), having been informed about the study objectives, agreed to take part in this program of functional rehabilitation based on motor activity. All of the patients were affected by peripheral arteriopathy at Fontaine s second stage and had presented with claudication after effort for at least 6 months. When necessary, a cardiological evaluation and stress test were performed, together with a physical exam to check for any excessively limiting factors or contraindications to the walking program.

Abstinence from smoking was required. No variations were made in prescribed medical therapy. No patients were taking β blockers.

Table 1 reports patient characteristics for age, weight, body mass index, principal risk factors, location of major vascular lesion at the start of the program.

A schematic description of the study design is shown in Figure 1.

Hemodynamic pattern evaluation

Under rest conditions, all patients underwent a duplex scanning examination (Technos, 3.5 and 7.5 MH probe, Esaote Biomedics, Genova, Italy) to evaluate the arterial hemodynamics of the lower limbs. The abdominal aorta, the common and external iliac, the common, superficial and deep femoral, the popliteal arteries, and both the tibial axes were evaluated. High resolution B-mode imaging, complemented by PW Doppler analysis for detection of arterial obstruction, as well as peak-flow velocity for definition of critical stenosis has been used according to standard.8,9 In addition, ankle pressure was measured in the posterior tibial and the dorsalis pedis arteries of both legs. The ankle-brachial index (ABI) was calculated using current methodologies.10 For each patient, ABI values were classified in 2 groups according to the limb having the better or worse hemodynamic situation. For brevity, the terms "better limb" and "worse limb" will be used hereafter.

Determination of the "pain threshold speed" with a treadmill walking test

The tests were performed in temperature-controlled environment of about 20C, equipped for medical emergencies. Functional evaluations were conducted in autumn and winter, between 9 a.m. and 12 p.m. Patients were asked to rest well prior to the test, to take their usual prescribed medicines, and to abstain from caffeine during the 12 hours preceding the test.

Comfortable clothing and habitually worn shoes were recommended. Each patient was fitted with a heart rate monitor (Sport Tester, Polar Electro, Finland), having an electrode belt and transmitter on the chest and a monitor on the wrist. The test procedure was clearly explained to the patients, who were asked to report immediately the onset of the cramping pain and to describe its intensity and location. Patients were asked to familiarize themselves with the motorized treadmill (Carnielli Fitness, Vittorio Veneto, Italy) by walking a few minutes on it at a low speed before the test. Patients who chose to grasp the handrail used it during all subsequent tests.

The test was preceded by a 1-min warm-up at a speed of 1.5 km/h. After a short recovery, the test began at 1.5 km/h with no slope, and slope was not increased during the test. Treadmill speed was progressively increased by 0.1 km/h every 10 m. Heart rate was recorded at the end of each 10m fraction. As soon as the patient reported the onset of painful cramping, the operator recorded the corresponding speed, or pain threshold speed (PTS), and heart rate (HRPTS). The test ended when the patient was unable to continue because of pain and had therefore reached the so-called maximal speed (S^sub max^). This speed and the corresponding heart rate (HRS^sub max^) were recorded. The protocol called for test interruption in case of dizziness or chest pain, or if the patient's heart rate reached approximately the maximal theoretical heart rate. The test would also be also interrupted if the patient was unable to keep up with the speed imposed by the treadmill for any nonvascular reason (e.g., age, biomechariical difficulties, joint pathology).

Figure 1.-The study design. *Data not shown. AP: ankle pressure; ABI: ankle-brachial index; PTS: pain threshold speed; MAS: maximal asymptomatic speed.

Figure 2.-Schematic representations of a testing session. The determination of the pain threshold speed (A) and the assessment of the maximal asymptomatic speed (B) are shown. The upper line represents the speed at onset of pain (PTS).

Assessment of the "maximal asymptomatic speed"

The purpose of this trial, carried out about 30 minutes after the end of the incremental test for PTS, was to determine the speed at which each patient was able to walk for at least 5 min with little or no pain. Following a 1-minute warm-up on the treadmill at 1.5 km/ h, the speed was increased progressively by 0.1 km/h every 10 m until the speed attained was 20-30% lower than predetermined PTS. This speed (maximal asymptomatic speed) was maintained for at least 5 minutes for patients with little functional reserve and for 10-15 minutes for patients in good general condition and with relatively little functional limitation. If the patient felt even a slight painful sensation, the speed was reduced until the symptom either disappeared or diminished to a minimum. At the end of the selected walking period, which resembled a training session, the test was interrupted by the operator. During the phase at constant speed the cadence of each patient was studied and recorde\d by an operator with the help of a digital metronome for music.

A schematic representation of a testing session is shown in Figure 2.

The proposed physical rehabilitation program

GENERAL CHARACTERISTICS

The program to be carried out at home was intended to be individualized, that is, adapted to the functional capacity, available time, and compliance possibilities of each patient. Results of the described functional evaluations were considered.

MODE AND DURATION

All patients were asked to perform walking sessions that ranged from 5 consecutive min, 2 to 4 times a day, to 30 consecutive min twice a day, according to their functional capacities.

INTENSITY

Walking intensity was established at a speed corresponding to the "maximal asymptomatic speed" of each patient. An adequate warm-up (5 to 10 min depending on the length of the training sessions) was recommended at a speed of 1.5-2 km/h, or in any case much lower than the training speed.

PACING

In order to facilitate training at the correct individual intensity, the patients were offered 3 training options:

* A time-based option, which prescribes an optimal time to complete a walking course of known distance habitually used by the patient. This course, usually outside but sometimes in the house, varied in distance from 10 to 1 000 m for our study population.

* A cadence-based option, which makes use of a metronome (available in music stores) and requires walking at a prescribed cadence, as recorded by the operator during the maximal asymptomatic speed assessment.

* A treadmill-based option, which utilizes a motorized treadmill, at home or at a gymnasium, at a prescribed speed.

Rehabilitation instructors were available to patients by telephone throughout the training period.

Training diary

Patients were asked to complete a daily record of the training carried out, noting their walking time, distance, and any associated symptoms. When possible, a close family member was given the responsibility of checking on the patient s training and of verifying the truth of the diary entries.

At the end of the 120-day training period, and before the test to determine the final PTS attained, the training diaries were collected and analyzed to evaluate compliance and to divide the patients into groups according the quality of the training performed. This grouping, carried out by 2 expert reviewers, placed the patients in 1 of 3 categories: trained (T), free walkers (FW), and untrained (U) depending on whether their training had been good, fair, or poor. The determining factors for assigning patients to these groups included: completed diary, average walking speed compared to that prescribed, number of walking sessions, adherence to prescribed training techniques, and any temporary interruptions due to intercurrent illness. If the reviewers' evaluations differed, the patient was placed in the less-trained group.

Statistical analysis

The statistical analyses of the changes induced both in the general study population and in the single groups at the end of the training period were performed using the Wilcoxon test.

Values are given as means SD. A p-value of 0.05 or less was considered significant.

TABLE II.-Hemodynamic and functional parameters of the study population (No.=29) at the beginning (O) and end (120) of the program.

TABLE III.-Training diary data.

Statistical analysis was performed by MedCalc statistical package 7.30 (MedCalc Software, Mariakerke, Belgium).

Results

Hemodynamic and functional parameters relative to the entire study population at the beginning and end of the program.

All of the patients completed the evaluation cycle. In 2 patients it was impossible to determine ABI due to vessel incompressibility. None of the tests in this study was interrupted for physical or technical reasons.

At the end of the program, the systolic blood pressure values decreased and the diastolic blood pressure was significantly lower (p=0.008). In the worse limb, AP rose, although not reaching the significance, whereas ABI significantly improved (p=0.01).

Figure 3.-Individual variations of the measured parameters at the beginning (O) and end (120) of the program. PTS: pain threshold speed; ABI: ankle-brachial index; AP: ankle pressure; T: trained group; FW: free walkers group; U: untrained group.

As for functional parameters, both PTS and Smax increased significantly (p=0.0001). During the final incremental test, 9 patients experienced only a mild warming sensation rather than painful cramping.

The data are reported in Table II.

Group placement and analysis of hemodynamic and functional parameters at the beginning and end of the program.

A summary of data from the training diaries is presented in Table III.

The T group

This group comprised 14 patients (13 males, 1 female) who carried out a considerable number of walking sessions at the maximal asymptomatic speed (Table III). The selected training modalities were: walking a measured course in a fixed time (n=3), walking at a predetermined cadence using a metronome (n=8), and treadmill walking at home or at a gymnasium (n=3).

T-group patients evidenced a decrease in average systolic blood pressure, a significant reduction in diastolic blood pressure (p<0.018) and increase in average AP in the limb with worse blood flow. Average ABI increased significantly (p<0.020). The percentage variations in this parameter were highly correlated to the variations in average AP for each patient (R^sup 2^=0.7734).

As regards the functional data, average PTS increased significantly (p<0.020). This increase was evidenced in all 14 patients (Figure 3) and in 6 of these the painful cramping during the incremental treadmill test was reduced to a mild warming sensation. In addition, in all T-group patients, PTS reached a value greater than or equal to 4.2 km/h, a speed that approximates a normal age-related speed of walking.11 The data are reported in Table IV. The individual variations that occurred are evident in Figure 3.

The FW group

This group comprised 7 patients (3 males, 4 females) who generally failed to observe the instructions relative to training intensity. All 7 patients did some training but carried out fewer walking sessions and at a lower speed than that proposed (Table III).

TABLE IV.-Hemodynamic and functional parameters of the groups trained (T) (n=J4), free walkers (FW) (n=7), and untrained (U) (n=8) at the beginning (O) and end (120) of the program. * p<0.05.

Systolic and diastolic pressures decreased, while average AP remained unchanged. Average ABI in the worse limb (unmeasurable in 2 of the 7 patients) increased from 0.500.11 to 0.580.12. The small size of the sample did not allow the statistical analysis.

Average PTS rose from 3.31.1 to 3.80.9 km/h. In all of these patients the painful cramping experienced during the initial incremental test was considerably reduced, and 3 of them described it as a mild warming sensation. The data are reported in Table IV. The individual variations occurred are evident in Figure 3.

The U group

This group comprised of 8 patients (3 males, 5 females). Of these 8 patients, 6 did not turn in a diary, but instead reported a general (not daily) walking activity without the use of any pacing techniques to ensure exercise intensity. The other 2 patients presented diaries that reported a reduced number of walking sessions due to intercurrent illnesses or acute phases of chronic pathologies. No hemodynamic modifications were detected in the U group. There was a slight increase in average PTS (from 2.10.4 to 2.4 0.3 km/h) and in average S^sub max^. The data are reported in Table IV. The individual variations occurred are evident in Figure 3.

Discussion

Patients with PAOD have to provide enough energy to satisfy the metabolic demand in the hypoxic area.12 To resolve this problem, surgical measures aimed at increasing blood flow in the ischemie muscle are employed, as well as metabolic agents such as carnitine.12

An analogous result can be attained through exercise, which could be able to stimulate vascular remodeling 13 and to develop an increase in the number of mitochondria and in the level of oxydative enzymes.5,14 Similar modifications in respiratory muscle capacity are mainly induced by endurance training at selected intensities.5,I5,16

The knowledge that exercise is effective in treating this pathology ' renders advisable and even necessary the employment of training programs.17 Patients in home-based training programs are instructed to walk at their individual speed and to continue walking after pain onset.18 In supervised programs on a treadmill, an exercise intensity is used that initially brings on claudication pain and continues tolerating a submaximal level of pain.19 The idea is "that exercise causing the greatest amount of ischemia may be most effective in the treatment of claudication" and that "maximal pain at high intensity may be appropriate to stimulate adaptive responses".20 Training improves effectively exercise tolerance in patients and promotes significant improvements in walking distance.21 These high-intensity sessions are not, however, followed by improvements in aerobic capacity, but rather by disturbances in the oxidative metabolism, by signs of activation of anaerobic mechanisms, and by skeletal muscle denervation.4 High-intensity exercise is known in fact to impair muscular function and respiratory capacity of the working muscle,22,23 but at the same time a low local oxygen concentration is an adequate, independent stimulus for the oxidative metabolic capacity.24,25 For this reason, training should combine appropriate exercise intensity with an adequate duration. Experts in sports training recognize that at exercise intensities greater than the anaerobic threshold, the total volume of training is limited and that training at about the intensity associated with the anaerobic threshold the intensity- duration relationship is optimized.\16

For all of the above reasons, we have hypothesized that the target intensity level of exercise training in patients with arteriopathy could represent a strategic device to optimize the intensity-duration relationship. Appropriate levels of exercise have been determined for patients with coronary artery disease (target heart rate), for those with chronic obstructive pulmonary disease (dispnea ratings), and for other, generally healthy populations such as the elderly (perceived exertion rating).27-29

The original aspect of our study is the application of properly developed evaluation and training methods, based on individual PTS measurement 6,7 and on a submaximal training intensity, the maximal asymptomatic speed. Our objective was to establish an optimal training speed for each subject, thereby enabling the arteriopathic patient to increase the walking distance at an exercise intensity that would prove beneficial while producing little or no lactate accumulation and pain. Given the difficulty in determining a more precise training speed that would correspond to muscle lactate accumulation in the worse limb, we utilized an easier and economical method of determination, that of PTS, which represents an anaerobic intensity. We realized that at speed progressively below PTS training sessions could be progressively prolonged. In particular we observed that at a walking speed 20-30% below PTS, at the "maximal asymptomatic speed", the patient was able to carry out 5- to 30- minute training sessions, according to his or her functional capacity (personal observation). Similarly, if in endurance events the running performance is closely related to the velocity at which a blood lactate accumulation of 4 mmol/L occurs,30 runners appear to set a race pace at a lower velocity, in order to utilize the largest possible oxygen consumption avoiding the exponential rise in plasma lactate. This so-called "maximal steady-state running pace" for various events elicits in fact 2 mmol/L lactate.3 1.32

Once the problem of prescribing exercise intensity was resolved, we needed to find a way to help the patient adhere to that intensity. Pacing is useful so that the individual speed, recommended by some authors,18 often is excessive with respect to that permitted by the ischemia. In addition, patients with reduced functional capacity experience great psychological difficulty in walking at speeds (e.g. 2-2.5 km/h) that are well below those that come naturally or that they were used to (about 4 km/h)l ' before their pathology worsened. Thus, a method was needed that would help patients reproduce their optimal training intensity at home. Among those proposed, cadence, used to pace training in sports such as cycling or rowing, seems to be particularly effective, easy and economical.

On the basis of these concepts-optimal exercise intensity, prescription and execution modalities-we examined the general and specific effects of the program according to the compliance demonstrated. There are two main results to take into consideration. The first is the general efficacy of the home-based program. The decrease in systemic blood pressure and the increase in ankle pressure are interesting and resulted in a significant increase in ABI. From a functional point of view, there was a distinct rehabilitative effect, with an average increase in the critical speed to pain of more than 20% and an approximation of the normal walking speed for subjects of the same age.11 Corresponding heart rates at the final PTS were similar to those at the starting PTS, indicating improved cardiovascular efficiency. The second fundamental result is the considerable efficacy of submaximal exercise shown in the T group. This group was best at following the training program in terms of exercise intensity, duration, and technique. T-group patients obtained, above all, increases in ankle pressure in the worse limb with consequent and correlated increases in ABI. They showed impressive improvements in PTS (+50%) and either dramatic reductions in, or disappearance of, painful symptoms.

This being a preliminary study, we do not want to draw hasty conclusions, because the data in our possession don't permit us to explain if the modifications that occurred are related to the improvement of the aerobic function and/or a concomitant development of the collateral circulation. However, in some patients, we observed an evident collateral development by means of the duplex scanning (personal observation), confirming the increase in calf blood flow after training previously reported.33,34 Even if our duplex observation is unquantifiable, shear stress, conditions of local acidosis and exercise are considered favorable factors for vascular remodeling.13, 35 Moreover, a regular aerobic leg exercise was even found to induce femoral artery expansive remodelling in healthy adult men following a submaximal training stimulus.36 The performance of the T group demonstrates that it is possible to set up home-based rehabilitation programs in an arteriopathic population, even if in some subpopulations supervised exercise could bring better results. It could be argued that the T group presented functional values and average ABI that were higher than those of the other groups, or relatively minor problems related to chronic pathologies, or a higher number of male subjects. The fact is that some patients in the FW and U groups, who at the beginning of the program had ABI and PTS values that were comparable to those of some T-group patients, failed to attain the same results (Figure 3).

The general compliance in this study can be considered satisfactory: a good portion (21 out of 29) of the patients trained with commitment and diligence. Some attributed their compliance to the "tolerability" of the training method and to the distancing, even psychological, from the painful symptom. Gradually realizing that they were able to walk for longer distances without having to stop, these patients dedicated themselves to the exercise training with continuity. A significant improvement of the quality of life perception was also documented (data not shown). In addition, the minimal use of the available telephone communication served as evidence of the simplicity of the program. A limitation that could be ascribed to our study is the lack of a control group of arteriopathic patients who made no changes in their physical activity for the 120-day period. It is known that subjects with chronic degenerative pathologies do not show improvements in function or ABI if not treated. While our study did not include a true control group, this role could be attributed to the U group, which, though not completely passive, showed no variations. Another factor that could seem to be a limitation but that, in our opinion, is an advantage is the low standardization of the proposed rehabilitation program. Sacrificing part of the standardization for individual patients is necessary and fundamental, especially in pathologies where the different locations and characteristics of the lesion and the wide variety of associated morbid conditions (nephropathy with anemia, diabetes and diffused artheriosclerosis, cardiopathy, etc.) require diversified approaches to treatment.

Conclusions

In conclusion, this study proposed to develop a home-based rehabilitation methodology based neither on mild aerobic nor purely anaerobic exercise, but rather on submaximal training. The preliminary data seem to confirm the initial hypothesis. This pilot program has shown promise in the areas of patient compliance and improvements in hemodynamic and functional parameters. Additional and more in-depth investigation, such as randomized controlled trials versus traditional exercise programs, should be considered on the basis of the reported results.

Acknowledgements.-We wish to thank Ms. Francesca Pancaldi for skilled technical assistance and Ms. Patricia Ennis for translating and editing the article.

This paper has been presented at 21st World Congress of the International Union of Angiology (May 22-26, 2004; Rome, Italy) and selected for the IASACO Prizes Session.

Received August 9, 2004; accepted for publication September 6, 2004.

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F. MANFREDINI, F. CONCONI, A. M. MALAGONI, R. MANFREDINI, N. BASAGLIA, F. MASCOLI, A. LIBONI P. ZAMBONI

Vascular Diseases Center, University of Ferrara, Ferrara, Italy

Address reprint requests to: F. Manfredini, MD, Centre Studi Biomedici Applicati allo Sport, Universit di Ferrara, Via Gramicia 35,1-44100 Ferrara, Italy. E-mail: mdf@unife.it

Copyright Edizioni Minerva Medica Dec 2004

Source: International Angiology

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