Low-Velocity Graded Treadmill Stress Testing in Hemiparetic Stroke Patients
Background and Purpose Coronary artery disease is prevalent in stroke patients and is an important factor affecting rehabilitation and health outcomes. However, the presence of neurological deficits in gait and balance has discouraged systematic application of exercise testing and prescription in the stroke population. We evaluated a novel graded treadmill stress test in paretic stroke patients and tested floor walking as a predictor of adequate neurological function to perform the treadmill test.
Methods Patients (n=31) with residual paretic gait deficits after ischemic stroke were evaluated with graded treadmill at gait velocities individualized to functional mobility observed during an initial zero-incline treadmill tolerance test.
Results Most patients (30/31) tolerated testing, achieving mean heart rates of 129±14 beats per minute (mean±SD), representing 84±10% of maximal age-predicted heart rate. Evidence for asymptomatic myocardial ischemia was found in 29% of those without known coronary artery disease. Exercise termination was more often due to generalized fatigue than cardiopulmonary intolerance (23/31 versus 4/31; P<.0001) or hemiparetic leg fatigue (1/31; P<.0001). Floor walking across a wide range of velocities (0.25 to 2.5 mph) demonstrated a strong linear relation with treadmill velocities (n=24; r=.80; P<.0001); all patients floor walking at ≥0.5 mph had adequate neuromotor function to perform the exercise test.
Conclusions These findings suggest that graded treadmill exercise testing, with proper safety precautions, can be used to assess cardiopulmonary function in paretic stroke patients. A simple floor-walking test predicts adequate neurological function to perform the exercise test. Exercise capacity is most limited by generalized fatigue and not by the paretic limb, supporting a rationale for endurance training in this population.
Treadmill exercise testing is widely used as a primary screening tool for detecting CAD and provides vital information for proper design of cardiovascular exercise prescription.1 2 Cardiovascular comorbidity is prevalent in the stroke population, and cardiac death remains the leading cause for mortality in long-term stroke survivors.3 4 5 Although customized treadmill exercise protocols are proposed for the elderly and patients with comorbid conditions limiting exercise capacity,2 6 no such protocols have been validated in stroke patients with documented neurological deficits affecting gait and balance. Cardiac stress testing has been demonstrated to be safe and effective only in cerebrovascular disease patients with transient or minor neurological deficits.7 8 9 Pharmacological stress tests remain reliable for detecting CAD in stroke patients but are costly as an initial screening modality and inadequate to define the cardiopulmonary response to physical exertion.10 11 Hence, the presence of significant neurological deficits affecting gait and balance has discouraged systematic application of exercise testing and proper cardiovascular exercise prescription in the paretic stroke population.
The present study investigated a customized low-velocity graded treadmill exercise protocol in stroke patients with a wide range of paretic gait abnormalities. We examined the hypothesis that older paretic stroke patients, although limited in gait velocity, could still achieve exercise intensities adequate for cardiopulmonary assessment using treadmill at progressive workloads by increasing inclines. A simple floor-walking test was also examined as a predictor of adequate neurological function to tolerate the treadmill task. Since prevalence of ischemic stroke is much greater in older individuals12 and chronic disability with advancing age further delimits exercise capacity,13 14 15 we chose to study mostly older patients. Our purpose, in the setting of an ongoing endurance training study, was to evaluate the safety and efficacy of this maximal effort treadmill test in the design of cardiovascular exercise prescription for older paretic stroke patients.
Subjects and Methods
Patients with residual hemiparetic or bilateral paretic gait abnormalities after ischemic stroke (>3 months prior) were recruited from the Baltimore Department of Veterans Affairs Medical Center and University of Maryland Medical System to participate in an ongoing aerobic exercise study. Evaluation included medical history, physical and neurological examinations, resting 12-lead ECG, and calculation of body mass index (weight [kilograms] divided by height [meters] squared). Usual medications were maintained throughout the period of screening and exercise testing. Exclusion criteria included congestive heart failure, unstable angina, peripheral vascular disease, orthopedic conditions, and other medical or neuropsychiatric conditions (eg, significant dementia) limiting participation in a low-intensity aerobic exercise research program. This study was approved by the Institutional Review Board, and all patients gave informed consent.
Self-selected floor-walking velocities were determined from 30-foot timed walks.16 Patients were instructed to ambulate using the same comfortable speed, assistive device, and any orthosis normally used while ambulating in their own place of residence. Mean floor-walking velocities calculated from the three best of six trials were expressed in miles per hour to facilitate comparison with treadmill speeds. Only patients capable of ambulating at least 30 feet with an assistive device (eg, quad cane, walker) and/or close supervision, as necessary, were considered for study entry.
Exercise Treadmill Testing
An initial treadmill tolerance test without incline was used to assess gait stability, acclimatize patients to the exercise task, and identify the target velocity for subsequent maximal effort graded treadmill testing. Exercise tests were performed with a SensorMedics Max 1001 treadmill (SensorMedics) with continuous ECG and monitoring of vital signs. The zero-incline treadmill tolerance test was started at 0.5 mph and slowly advanced by 0.1-mph increments according to patients’ subjective tolerance and observer-rated gait stability. All tests were conducted by the same physician familiar with gait evaluation (R.F.M.), and testing was terminated on the patient’s request, if gait instability or cardiovascular decompensation was observed, according to guidelines of the American College of Sports Medicine.2 Handrail support was allowed ad libitum, and patients were instructed to minimize handrail support to that necessary for stabilizing balance. A belt support and close supervision were provided as safety measures, but no assistance was provided unless gait difficulties were observed.
Patients capable of performing ≥3 consecutive minutes of treadmill walking at ≥0.5 mph were given a 15-minute interval rest and then underwent graded treadmill exercise testing using a modification of the Harbor Protocol.17 This maximal-effort, constant-velocity graded treadmill test was performed at the target gait velocity previously determined from the zero-incline treadmill tolerance test, with the same continuous monitoring of ECG, vital signs, safety precautions, and criteria for exercise study termination. During the initial 2 minutes, subjects walked on the treadmill without an incline, followed by 2 minutes at 4% incline, with the incline advanced 2% per 2 minutes thereafter.
Peak exercise intensities were expressed as a percentage of maximal age-predicted heart rate (HRmax) according to the following formula1 : Predicted HRmax=220−Age (years). Since physically deconditioned patients may sometimes have a rapid heart rate response at minimal physical exertion, we further examined the RPP as an index of myocardial oxygen consumption.18 The RPP values at standing rest and immediately after exercise were calculated as the product of heart rate and systolic blood pressure divided by 100. Myocardial ischemia was defined as ≥1 mm ST-segment depression according to the Minnesota Code criteria.19 Baseline ECG abnormalities were considered in the interpretation of all stress tests, with ≥2 mm ST-segment depression beyond baseline accepted as significant in the event of baseline ST-segment depression.
All data are expressed as mean±SD. Simple regression analysis was used to examine relationships between floor walking velocities and the velocities used during treadmill exercise testing. χ2 was used to compare the frequency of categories for exercise termination.
We evaluated 31 stroke patients, including 22 black men, 6 white men, and 3 black women. Clinical and demographic features of the patients are shown in Table 1⇓. Three of 7 patients with known history of CAD had prior coronary artery bypass surgery; the remaining 4 patients had previously been hospitalized for myocardial infarction. None of these patients had participated in conventional cardiac rehabilitation. Of the remaining 24 patients without history of cardiac disease, 11 of 24 (46%) had abnormal resting ECGs, including meeting criteria for left ventricular hypertrophy (n=6), nonspecific ST-segment abnormalities (n=1), or both (n=4). All patients were in normal sinus rhythm, and none were receiving digitalis medications. Most patients with a history of hypertension (19/22) were receiving antihypertensive therapy, including three on β-blocker medications. Although target heart rates are more likely achieved if β-blockers are stopped before exercise testing, we continued these medications throughout the period of testing to maintain those conditions anticipated in a clinical exercise rehabilitation program.
Hemiparetic gait abnormalities were present in 28 patients, and 3 patients had lower extremity paraparesis due to bilateral hemispheric brain infarctions (n=2) or basilar artery thrombosis (n=1) with bilateral pontomesencephalic infarction. Most patients (19/31; 61%) used a single-point cane during some or all routine daily ambulation. Five patients with mild deficits (16%) preferred not to use an assistive device, and 7 (23%) relied heavily on a wheelchair for mobility but were capable of ambulating with a quad cane (n=5), a single-point cane (n=1), or a walker with standby aid (n=1) for at least 30 consecutive feet on a smooth surface. Mean self-selected floor-walking velocity determined from a subset of patients (n=24) was 1.6±0.6 mph, typical for a hemiparetic stroke population. A wide spectrum of gait impairment was further indicated by floor-walking velocities ranging from 0.25 to 2.5 mph.
Most patients (30/31) tolerated treadmill exercise to an end point of peak volitional effort or until cardiopulmonary signs prompted study termination by the monitoring physician (Table 2⇓). No patients had angina during exercise testing. One patient could not perform the zero-incline treadmill tolerance test because of gait instability and was not advanced to graded treadmill testing. This patient was obese (body mass index=32) and predominantly wheelchair bound, with a limited floor-walking capacity (0.25 mph) that was slower than the minimal operating velocity of our treadmill (0.5 mph). All patients with self-selected floor walking velocities ≥0.5 mph had adequate neurological function to perform the graded treadmill test with continuous handrail support and no assistance from the standby aid. Self-selected floor-walking velocities demonstrated a strong linear relation (r=.80, P<.0001) with those velocities used on graded treadmill exercise testing (Figure⇓).
Treadmill performance characteristics of 30 paretic stroke patients are shown in Table 3⇓. As a group, stroke patients achieved a mean of 84% of predicted HRmax. Half (15/30) achieved >85% of predicted HRmax, while 87% (26/30) reached >75% of predicted HRmax. In those 4 patients not achieving >75% of predicted HRmax, concurrent use of β-blocker medications (n=2), early exercise termination due to dyspnea (n=1), and previously asymptomatic leg claudication unmasked by exercise (n=1) accounted for the lower heart rate responses. Excluding those on β-blocker medications and whose peak exercise heart rate was limited by leg claudication or early study termination, patients (n=26) achieved a mean of 86.3±9% of predicted HRmax. RPPs were available for 28 of 30 patients performing the treadmill test; 2 patients had immediate post-exercise blood pressures measured ≥1 minute after exercise and were excluded from this analysis. The mean RPP at standing rest was 101.3±12.9 and increased to 236.1±48 with exercise, constituting a mean 133% increase in RPP attributable to the exercise task.
In those patients with prior known CAD (n=7), gait instability on the treadmill tolerance test (n=1), hip pain due to arthritis (n=1), and significant ST-segment depression with sinus tachycardia at low exercise intensity (n=1) precluded entry in our ongoing exercise research program. Two of the remaining patients with known CAD had findings consistent with silent, reversible myocardial ischemia on reaching exercise intensities of 76% and 81% of predicted HRmax. In 24 patients lacking prior history of ischemic heart disease, 7 (29%) had abnormal stress tests suggesting silent and reversible myocardial ischemia, including significant ST-segment depression (n=5), increased premature ventricular contractions accompanied by ST-segment depression (n=1), and dyspnea at low exercise intensity (n=1). Subsequent thallium-201 radionuclide imaging showed reversible myocardial perfusion in 5 of 6 patients studied; 1 patient had no perfusion abnormalities despite reproduction of ST-segment depression during exercise testing. One patient with only marked dyspnea at low exercise intensity was further evaluated, including with angiography, and was found to require elective coronary artery bypass surgery.
Cardiovascular comorbidity in stroke patients is an important clinical factor affecting both rehabilitation and long-term health outcomes.3 4 5 20 21 However, exercise stress testing is not systematically used in screening for CAD or as a basis for implementing cardiovascular exercise prescription in paretic stroke patients.22 This may be due to concerns regarding risk of falls or a lack of evidence to date that patients with neurological deficits compromising gait and balance can adequately perform treadmill exercise. We performed cardiac stress testing on 31 older paretic stroke patients using a customized low-velocity graded treadmill protocol and found that most patients (97%) tolerated this task and could achieve exercise intensities useful in screening for CAD and subsequent design of exercise prescription. Furthermore, a self-selected floor-walking velocity of ≥0.5 mph, albeit with an assistive device and/or standby aid, appeared to predict adequate neurological function to perform this graded treadmill test.
Patients with cerebrovascular disease often have coexistent CAD.4 5 Using treadmill testing with radionuclide imaging, Rokey et al7 found that 58% of consecutive cerebrovascular disease patients had evidence of significant CAD. Treadmill testing with thallium-201 scintigraphy revealed abnormalities consistent with silent and reversible myocardial ischemia in 28% of consecutive cerebrovascular disease patients without prior known history of ischemic heart disease.8 Similarly, results from our exercise tests provided evidence of silent and reversible myocardial ischemia in 7 of 24 paretic stroke patients (29%) without prior known history of CAD. Five of these patients had abnormal thallium scintigraphy, and another had significant disease at catheterization. Thus, a high percentage of hemiparetic stroke patients with abnormal exercise stress tests had additional evidence supporting the diagnosis of CAD and silent myocardial ischemia.
Few studies have examined exercise capacity in elderly stroke patients. Prior studies used a Bruce protocol to evaluate somewhat younger cerebrovascular disease patients with history of only transient or minor neurological deficits.6 7
Our patients were approximately a decade older. and all had residual deficits representing a wide range of paretic gait disturbance. On the basis of their observed treadmill exercise capacities, none could have tolerated a conventional Bruce protocol. However, most could perform the customized low-velocity graded treadmill protocol to an end point of volitional fatigue or cardiopulmonary exercise intolerance. Using a modified supine bicycle ergometry test, Moldover and Daum8 found that only 2 of 11 older hemiparetic stroke patients (mean age, 71 years) could achieve >85% of HRmax and, as a group, had a median 55% increase in RPP with exercise. In contrast, elderly stroke patients in the current study achieved a mean of 86% of HRmax and 133% increase in RPP, indicating a robust heart rate response and myocardial oxygen demands at peak exercise. These findings suggest that customized graded treadmill is a more effective modality for exercise testing in older paretic patients.
Surprisingly, volitional generalized and/or bilateral leg fatigue, not hemiparetic leg fatigue (23/31 versus 1/31; P<.0001) or cardiopulmonary intolerance (4/31; P<.0001), were the reasons for exercise termination in most patients. Thus, physical deconditioning rather than the paretic limb per se appears to be the most important factor limiting peak exercise capacity in this population. Bicycle endurance training improves cardiovascular exercise fitness levels in chronic hemiparetic patients,23 and we have shown that 6 months of treadmill endurance training produces progressive and linear reductions in the energy expenditure and cardiovascular demands of submaximal effort hemiparetic treadmill walking in older stroke patients.24 Further studies are needed to determine whether systematic exercise testing and aerobic training improve cardiovascular health outcomes or functional mobility in the chronic stroke population.
Interpretation of this study is limited by small sample size, lack of angiographic confirmation of presumptive CAD suggested by stress testing, and the chronicity of neurological conditions in this selected stroke series. We studied only chronic paretic patients who had already completed stroke rehabilitation. Care must be taken in extending these results to acute stroke patients. Abnormal cardiopulmonary responses that may accompany exercise (eg, hypotension, cardiac dysrhythmia) could threaten perfusion to dependent ischemic brain tissue during the early poststroke period when cerebral autoregulation is most often impaired.25 26 A greater proportion of subacute stroke patients not yet completing conventional rehabilitation may be physically unable to perform the treadmill test. Since cardiovascular comorbidity is an important factor affecting stroke rehabilitation planning and outcomes,5 20 21 22 there is a clinical need to better understand the utility of exercise testing in this early poststroke period.
In summary, we report that a customized treadmill exercise protocol is well tolerated and adequate to define the cardiopulmonary response to strenuous physical exertion in older stroke patients with a wide range of paretic gait deficits. A simple timed walking test appears to predict which patients have adequate neurological function to perform the treadmill test. Results from exercise testing suggest that silent and reversible myocardial ischemia is present in a substantial proportion (29%) of stroke patients without prior known CAD and provide essential information for proper design of exercise prescription in those with CAD. Customized “low-velocity” treadmill, with proper safety precautions, should be considered a cost-effective screening modality to assess cardiopulmonary function and to facilitate design of cardiovascular exercise prescription in the paretic stroke population.
Selected Abbreviations and Acronyms
|CAD||=||coronary artery disease|
|HRmax||=||maximal age-predicted heart rate|
This study was supported in part by the Baltimore Veterans Administration Geriatrics Research, Education, and Clinical Center, with a Veterans Health Administration Research Advisory Group grant (12A7A) to Dr Macko. Drs Macko and Silver were recipients of a pilot grant from the Claude D. Pepper Older Americans Independence Center from the National Institute on Aging (P60-AG12583). The authors wish to acknowledge Dr Andrew P. Goldberg for his support and Dr Nathan Carliner for his careful review of the manuscript.
- Received November 11, 1996.
- Revision received February 24, 1997.
- Accepted February 26, 1997.
- Copyright © 1997 by American Heart Association
Fletcher GF, Schlant RC. The exercise test. In: Schlant RC, Alexander RW, eds. The Heart: Arteries and Veins. 8th ed. New York, NY: McGraw-Hill Publishing Co; 1994;423-440.
Kenney WL, Humphrey RH, Bryant CX, Mahler DA, Froelicher VF, Miller NH, York TD. American College of Sports Medicine: Guidelines for Exercise Testing and Prescription. Philadelphia, Pa: Lea & Febiger; 1991.
Sacco RL, Wolf PA, Kannel WB, McNamara PM. Survival and recurrence following stroke: the Framingham Study. Stroke. 1982;13:290-295.
Roth EJ. Heart disease in patients with stroke: incidence, impact, and implications for rehabilitation, part 1: classification and prevalence. Arch Phys Med Rehabil. 1993;74;752-760.
Wasserman K, Hansen JE, Sue DY, Whipp BJ, Casaburi R. Principles of Exercise Testing and Interpretation. Philadelphia, Pa: Lea & Febiger; 1994:95-111.
DePasquale G, Androeli A, Pinelli G, Grazi P, Manini G, Tognetti F, Testa C. Cerebral ischemia and asymptomatic coronary artery disease: a prospective study of 83 patients. Stroke. 1986;17:1098-1101.
Leppo J, Boucher CA, Okada RD, Newell JB, Strauss W, Pohost GM. Serial thallium-201 myocardial imaging after dipyridamole infusion: diagnostic utility in detecting coronary stenosis and relationship to regional wall motion. Circulation. 1982;66:649-657.
Sirna S, Biller J, Skorton DJ, Seaboid JE. Cardiac evaluation of the patient with stroke. Stroke. 1990;21:14-23.
Whisnant JP. Issues in stroke in the elderly. In: Dunkle RE, Schmidley JW, eds. Stroke in the Elderly. New York, NY: Springer Publishing; 1984:19-26.
Holden MK, Gill KM, Magliozzi MR, Nathan J, Piehl-Baker L. Clinical gait assessment in the neurologically impaired: reliability and meaningfulness. Phys Ther. 1984;64:35-40.
Buchfurer MJ, Hansen JE, Robinson TE, Sue DY, Wasserman K, Whipp BJ. Optimizing the exercise protocol for cardiopulmonary assessment. J Appl Physiol. 1983;55:1558-1564.
Kitamuri K, Jorgenson CR, Gobel FL, Taylor HL, Wang Y. He-modynamic correlates of myocardial oxygen consumption during upright exercise. J Appl Physiol. 1972;32:516-522.
Prineas RJ, Crow R, Blackburn H. The Minnesota Code Manual of Electrocardiographic Findings. Littleton, Mass: John Wright Publishing; 1982:1-229.
Roth EJ, Mueller K, Green D. Stroke rehabilitation outcome: impact of coronary artery disease. Stroke. 1988;19:42-47.
Wade DT, Skilbeck CE, Wood VA, Hewer RL. Long-term survival after stroke. Age Ageing. 1984;13:76-82.
Gitter A, Halar EM. Cardiac rehabilitation of the patient with stroke. Phys Med Rehabil Clin North Am. 1995;6:297-310.
Potempa KL, Lopez M, Braun LT, Szidon P, Fogg L, Tincknell T. Physiological outcomes of aerobic exercise training in hemiparetic stroke patients. Stroke. 1995;26:101-105.
Macko RF, DeSouza CA, Tretter L, Silver KH, Smith GV, Anderson PA, Tomoyasu N, Gorman P, Dengel DR. Treadmill aerobic exercise training reduces energy expenditure and cardiovascular demands of hemiparetic gait in chronic stroke patients: a preliminary report. Stroke. 1997;28:326-330.
Irwin S, Tecklin JS. Cardiopulmonary Physical Therapy. 3rd ed. New York, NY: CV Mosby Co; 1995:92-105.
Baron JC. Positron emission tomography studies in ischemic stroke. In: Barnett HJM, Stein BM, Mohr JP, Yatsu FM, eds. Stroke: Pathophysiology, Diagnosis, and Management. 2nd ed. New York, NY: Churchill Livingstone, Inc; 1992:111-124.