CV Disability Statistics
Approximately 900 000 individuals receive CV disability payments.2(pp54-55) The number of adult CV claims submitted varies modestly from year to year and has averaged 145 000 claims annually for the past 20 years.2(p55) Although the allowance rate using the 5-step process has remained constant at about 40%, there has been a shift in the step where the majority of allowances occur from step 3 to step 5. In 1990, approximately 60% of allowances occurred at step 3 compared with only 26% in 2008.2 Step 3 allowances are determined by SSA state agencies called Disability Determination Services, where most teams are composed of 2 people, a lay disability examiner and a physician. Allowances at steps 4 and 5 are more laborious, expensive, and time-consuming and commonly are resolved before an administrative law judge.
2010 Recommended Revision of the CV Listings
The SSA CV listings are periodically revised with the latest recommended revision occurring in 2010. The SSA asked the Institute of Medicine (IOM) to convene an expert panel to incorporate advances in the diagnosis and treatment of CVD into the Listings,2 with the goal of shifting more of the allowances from steps 4 and 5 to step 3 for individuals who are ultimately awarded disability, making the process more efficient and economical.
During their deliberations, the IOM Committee noted that there was significant underutilization of the exercise test (ET) in the disability evaluation process. Social Security Administration examiners have the authority to order selective noninvasive tests, including an ET, when this information is absent from the applicant medical records. However, SSA examiners generally have been reluctant to order an ET for several reasons, including concern about the safety of testing, lack of clinical familiarity with the applicant, uncertainty concerning ownership of the test results, and subsequent medical management of the applicant. Broader use of an ET, especially a cardiopulmonary exercise test (CPX), would enhance the objectivity of the disability determination process and facilitate the application of the Listings.
Each of the individual CV Listings (as proposed by the 2010 IOM Committee) shares the requirement for a CV anatomical abnormality plus a functional limitation (with a few exceptions). The anatomical abnormality is specific to each Listing, whereas the functional impairment is a common pathway for the majority of the Listings and reflects an inability to perform activity requiring 5 metabolic equivalents (METs) of energy expenditure. The requirement for a functional limitation relates to the highly variable impact on physical capacity of patients with the same anatomical disease. If the results of an ET are not available in the applicant medical record, functional capacity can be determined from the applicant's limitations of activities of daily living described in the medical record or by the requirement for ≥ 3 hospitalizations during the preceding year to treat the condition.2 This latter criterion reflects both the difficulty of stabilizing the medical condition and the challenge for the applicant to maintain a job in the face of frequent absences to receive hospital medical treatment.
ASSESSMENT OF FUNCTIONAL CAPACITY
A comprehensive examination of functional capacity is a primary component of disability assessment. Cardiac rehabilitation programs represent an ideal setting for the systematic assessment of cardiac disability. Both aerobic capacity and muscle force production should be included in the quantification of functional capacity. The different approaches to functional capacity assessment are detailed in the following sections, and the methods for assessing functional aerobic capacity are summarized in Table 2.
Aerobic Capacity Assessment
A CPX incorporates ventilatory expired gas analysis with traditional ET procedures, as reviewed elsewhere.6,7 The use of CPX allows the most accurate quantification of aerobic capacity, expressed as peak oxygen uptake (
O2) in mL·kg−1·min−1. A peak aerobic capacity of 15 mL·kg−1·min−1 has been proposed as a key threshold for disability assessment.2(pp14-15,18) While an individual at or below this peak
O2 level is clearly limited, it is important to consider aerobic capacity in relation to unique energy demands of both the home and occupational setting.8 Since age and sex have a significant influence on aerobic capacity in normal circumstances, it is recommended that peak
O2 also be reported as a percent-predicted value, which can be derived from established regression equations.9 Ventilatory expired gas analysis also allows for the determination of exercise intensities that can be sustained for prolonged periods of time through the detection of ventilatory threshold, which is of particular value in individuals whose occupational requirements involve sustained periods of aerobic activity. Finally, peak respiratory exchange ratio (RER) defined as the ratio of carbon dioxide production and oxygen uptake provides an accurate determination of subject effort. Attainment of a peak RER ≥ 1.10 is widely recognized as a valid and reliable indicator of excellent patient exercise effort.1 When exercise is terminated at a peak RER < 1.00, in the absence of an abnormal exercise response (hemodynamic, electrocardiogram [ECG], pulse oximetry, etc), the peak
O2 obtained may not be a valid representation of the individual's true aerobic capacity.6
During a CPX, abnormalities detected in blood pressure (hypertension or hypotension), ECG (ST-segment changes, arrhythmias), and/or pulse oximetry (desaturation) should be documented. Rating of perceived exertion as well as angina and dyspnea should be quantified using established scales.7,10,11 Coupling abnormal responses with the exercise intensity at which they began is valuable in providing recommendations for activity/occupational modifications. Specifically, activities corresponding to workloads that surpass a threshold at which ischemic ECG changes, oxygen desaturation, onset of arrhythmias, or angina/dyspnea occur should be avoided.
Aerobic ET Without Ventilatory Expired Gas Analysis
Because of requirements for additional equipment and increased staff expertise, most ETs are performed without CPX. Aerobic capacity is estimated from the workload achieved on the given modality employed (ie, ergometer or treadmill) and is commonly expressed in METs, where one MET equates to 3.5 mL·kg−1·min−1. A peak MET level of 5 has been proposed as a key threshold for disability assessment.2(pp14-15,18) This equates to an estimated oxygen cost of 17.5 mL·kg−1·min−1, which is higher than the 15.0 mL·kg−1·min−1 threshold proposed when oxygen uptake is directly measured. This discrepancy is due to the fact that estimated aerobic capacity can significantly overestimate true
Logistical Considerations for Clinical Aerobic ET
Treadmill and lower extremity ergometry are the 2 most common modes utilized during ET. It is recommended that both modes be available to match the needs of the individual patient being assessed. For example, a patient with balance deficits or orthopedic limitations may have difficulty with treadmill ambulation and should ideally be tested on a cycle ergometer, although aerobic capacity is 10% to 20% lower on a cycle ergometer than on a treadmill.12 These mode-dependent differences in aerobic capacity should be considered during the disability assessment. When aerobic capacity is estimated from treadmill speed and grade, handrail use likely results in overestimation of actual peak
O2 and can potentially invalidate the results of the disability assessment. For example, the difference in recommended thresholds to define disability is 2.5 mL·kg−1·min−1 greater when estimating aerobic capacity from workload achieved. This discrepancy reflects the expected error associated with estimating aerobic capacity. The mean difference between estimated and measured aerobic capacity in patients undergoing ET for the evaluation of suspected myocardial ischemia was greater than 7 mL·kg−1·min−1.13 In this study, all subjects underwent an ET using the aggressive Bruce protocol and were allowed to use handrail support, both of which likely contributed to this large discrepancy in a synergistic fashion.
There are numerous ET protocols that vary greatly in the adjustment of workload between stages and, ideally, the ET should last about 8 to 12 minutes.12 The Bruce protocol is the most aggressive in terms of speed and grade adjustment and is an inappropriate choice for most, if not all, patients undergoing a disability assessment given that some level of aerobic impairment is expected in this population. The degree of error between estimated (METs) and measured
O2 is significantly higher when an aggressive protocol, such as the Bruce, is utilized.14,15 Use of conservative ramping protocols has been shown to minimize this discrepancy in patients with significant functional limitations16 and is recommended for patients undergoing a disability assessment.
Six-Minute Walk Test
The 6-Minute Walk Test (6MWT) is frequently used in populations with chronic diseases such as those with HF and chronic obstructive pulmonary disease to assess functional status and prognosis.17 Pulse oximetry, heart rate, ECG via telemetry, and subjective symptoms can be monitored during the 6MWT. Research has consistently demonstrated a large and clinically unacceptable standard error of estimate (∼3.8 mL·kg−1·min−1) using 6MWT distance to estimate peak
O2 in an individual patient.18 For this reason, the 6MWT may not be an ideal approach for disability assessment. A 6MWT distance of 300 m or less identifies patients with a poorer prognosis.12 Others have proposed a graded classification according to 6MWT distance to assess prognosis and clinical status.19 It has also been proposed that a 6MWT distance ≥ 500 m is considered a normal response during a disability assessment.3 Research is needed to identify 6MWT distance thresholds that accurately quantify the level of disability.
Questionnaires for Estimating Aerobic Capacity
Questionnaires, such as the Duke Activity Status Index, are available that estimate aerobic capacity.20–23 Although aerobic capacity estimated from these questionnaires statistically correlates with peak
O2 or METs achieved during ET, a considerable degree of error between questionnaire-estimated aerobic capacity and the ET response does exist. Thus, using questionnaires to quantify aerobic capacity for disability assessment is not currently recommended.
Computer Adaptive Testing
An assessment tool currently under study with the potential for determining physical function related to disability is Computer Adaptive Testing (CAT),24 which uses an extensive item pool specific to a diagnosis or condition and the patient rates his or her ability to perform each functional task addressed in the test items. The Computer Adaptive Testing software assesses previous patient responses to select subsequent items from the pool that are appropriate to the individual level of functioning. This results in fewer and unnecessary items being administered. The computer software also includes rules for starting, stopping, and scoring the test.
ASSESSMENT OF MUSCLE FUNCTION
Strength assessment and strength-related training goals are important components of exercise and potentially even more important in assessment of potential limitations pertaining to disabilities. Strength, endurance, and power are 3 aspects of function used to denote specific properties of muscle-related function.25 The shift from sitting in a chair to standing, for example, relies on strength, the maximum force produced by a muscle or group of muscles, generated by muscles in the lower limbs to facilitate the lift. Endurance is the separate but related capability to sustain repeated muscular contractions over time. One may rely on strength to lift groceries, but it requires endurance to carry them into a car. Endurance tends to be greater if the functional task entails a relatively smaller percentage of one's maximal strength. Power relates to the speed with which force can be implemented. Power characterizes critical timing of force generation, such that falling may be averted if force in a potentially stabilizing leg is sufficiently swift. Power has been correlated with mobility, independent of maximum strength.
The combination of muscle strength, endurance, and power are often critical for disabled individuals. It is also important to recognize the interconnection between muscle function and aerobic capacity. Adults lacking sufficient strength components predictably have diminished mobility. Impaired strength can result directly from an underlying disease (eg, degenerative disease) and be compounded by the effects of decreased physical activity (PA) and subsequent deconditioning that result from the disease limitations.
Despite the strong rationale to focus on strength, endurance, and power as elemental parts of disability evaluations, these assessments are not straightforward and are often omitted. No single test definitively evaluates composite muscle health. Assessments often vary with the muscle group being tested, the type and speed of contraction, the type of equipment, and the joint range of motion (ROM). Even patient size is relevant. Angles and acceleration of movement vary with the proportions between patient and equipment and potentially influence results. Muscle testing requires steps to achieve proper posture, consistent speed of movements, full ROM, and suitable warm-up.
Strength can be measured statically, with no overt muscle movement, or dynamically, wherein the muscle changes in length.26,27 Static or isometric exercise assessment is achieved by devices that measure force generated in the upper and lower extremities. Cable tensiometers and handgrip dynamometers are popular devices, because of their relative convenience and safety. However, because each assessment characterizes only a specific muscle group and angle, there are some limitations in their capacity to assess overall muscular strength. Most dynamometers are now size-adjustable, and recent guidelines on handgrip assessments reflect efforts to standardize techniques and increase reliability of assessments.27
Dynamic strength assessments are more complex, as they require measurement of force over the ROM, entailing concentric and eccentric contractions over time.26,27 Specialized isokinetic devices provide a technological mechanism to regulate speed and resistance to ensure stable resistance across the ROM. Although isokinetic assessment has a solid theoretical basis, it is seldom used in the clinical setting.
Traditionally, the 1-repetition maximum (1-RM) is the standard of dynamic assessment, that is, the maximum resistance that can be moved 1 time through the full ROM. Given that strength fluctuates across a ROM, the 1-RM reflects the weakest strength across the ROM. It is usually determined by adding weights (using free weights or an exercise machine) until an individual can no longer achieve a full ROM. 1-RM evaluations reflect inherent variability in regard to increments of resistance added until the 1-RM is determined: amount of time between tries; differences in warm-up, posture, spotting, speed of movement; the steps to ensure that full ROM is completed; and the fundamental motivation of the person being assessed. However, the 1-RM is often not used in clinical practice. Instead, clusters of RM, such as a 4-RM or even 6-RM, can be used and are particularly good for evaluating persons with disability or muscle weakness.
Endurance is assessed by measuring the number of contractions performed using a specific percentage of a 1-RM. Assessments can be made using timing of static contractions until fatigue, or measuring the number of active contractions until fatigue. Endurance assessments are not routinely incorporated into clinical evaluations but provide important perspective on general health and functional capacity.26–28 Among disabled adults, endurance assessments provide functional perspectives, which are useful in quantifying the clinical impact of limitations from disease or injury, and providing important benchmarks with which strength training and adjunctive care can be guided and monitored.
Power evaluations are even less commonly performed despite a growing body of literature highlighting their clinical relevance. Assessment of power requires expensive specialized equipment that measures 1-RM as well as percentages of 1-RM that are able to capture the associated timing dynamics. In general, peak power is lowest in relation to both very low and very high 1-RMs and greatest in relation to the movements at 60% to 85% of the 1-RMs. While this may seem too theoretical to recommend as part of standard assessment, the impact of power on mobility is unequivocal.29
Integrated Assessment Tests
While direct assessments of strength, endurance, and power are each inherently problematic, the conceptual utility of muscle performance assessment remains clear. An alternative approach is to consider integrative movement assessments that incorporate aspects of muscle strength in tests that reflect normal activities and that are relatively easy to administer. The 30-second chair stand test and the Timed Up and Go Test are 2 assessments commonly utilized as part of geriatric assessments that can be applied to others who may be weakened and/or susceptible to falls due to lack of strength.30–32 In the 30-second chair test, measurement of the number of times an individual can get in and out of a chair has been correlated to the 1-RM in older individuals and isometric assessments of quadriceps strength. High test-retest reliability has been demonstrated. Similarly, in the Timed Up and Go Test, measurement of how long it takes for a patient to rise from an arm chair, walk 3 m, turn, walk back, and sit down again has been validated as a predictor of falls. It has been used as a test of strength-related functional mobility, particularly in relation to frailty and/or disability.
ASSESSING PHYSICAL REQUIREMENTS OF JOB TASKS
It is often not feasible to perform CPX at the work site but CPX can be performed in the clinical laboratory while patients are duplicating their job tasks (eg, lifting, carrying heavy objects, climbing). From a practical standpoint, ambulatory monitoring is more easily carried out at the work site where heart rate can be determined for specific job tasks and compared to ET results. Ambulatory ECG monitoring provides useful heart rate and heart rhythm information. In some clinical situations where work-induced hypertension or hypotension is suspected, ambulatory blood pressure monitoring, either alone or combined with ECG monitoring, can also be performed during working conditions. While more precise testing can be performed in the laboratory (see the “Simulated Job Tasks” section), ambulatory monitoring has the advantage of assessing patients during true environmental conditions, as well as during psychological stress during working conditions.
The use of additional clinical expertise (eg, occupational therapist, physical therapist) may be helpful when conducting job task analysis. In addition, cardiac rehabilitation clinical staff may require additional training to assess job tasks.
Physical Requirements From the Literature
Several important sources have compiled data for a wide spectrum of human PA.8,33–35 Estimates of PA are limited by the use of many different sources with varied detail and methodology. In addition, data generally do not fully account for variations in climate, body size and composition, age, and gender. Various PAs are listed as multiples of the resting MET level ranging from sleeping (0.9 METs) to running at high speeds (eg, close to 11 mph or 18 METs). The compilation from various reports includes a wide range of PAs that include general PA, transport, domestic chores, various occupational activities (which are important to this manuscript), and sports and recreational activities for both genders.
ON-SITE JOB TASK ASSESSMENTS
Several investigations have monitored cardiac parameters during occupational tasks.36–40 Twenty-two male city bus drivers with ischemic heart disease performed an ET followed by telemetry, ambulatory blood pressure, and subjective symptom monitoring during work. Heart rate, blood pressure, and subjective symptoms were approximately half the values reached during the ET.36 On-the-job monitoring can be used to determine whether abnormalities manifested during the ET are reproduced during actual job tasks. This information can be used to structure recommendations for modified work assignments, if needed.
Initial research assessed CV responses during “less strenuous” occupations. More recently, research accurately quantifying the CV and metabolic demands of highly strenuous occupations, such as firefighters and police officers, has been conducted.39–41 Maximal heart rate responses during a fire-suppression simulation far exceeded the values obtained during a maximal ET in 49 young, apparently healthy male firefighters.39 In another study, heart rate and
O2 responses during a fire and rescue obstacle course exceeded the typically prescribed aerobic exercise training intensities in 23 apparently healthy male firefighters.40 Similar findings occurred in 30 apparently healthy police officers and cadets completing an obstacle course.41 Assessment in the workplace may not be necessary when the physiological response to exercise is normal and the peak aerobic capacity achieved exceeds physical demands for a given occupation. However, in occupations with extreme physical demands, a clinical ET may be insufficient to determine clearance to return to work. In such cases, a comprehensive functional assessment in the clinical setting in addition to a real or simulated work site assessment is recommended.
While ET constitutes the standard by which cardiac abnormality is customarily assessed, it does not account for potential instability that can be induced by mental strain.42 Adults who show no signs of cardiac instability during routine exercise assessments may develop ischemia, arrhythmia, and other manifestations of cardiac instability in a stressful employment environment. This is an additional reason to conduct a disability assessment in the workplace. Telemetry or ambulatory ECG monitoring during workplace assessment may reveal significant consequences that are otherwise not apparent. Additional research is needed to resolve issues related to work site assessment and establish its value.
SIMULATED JOB TASKS
Simulating selected physical requirements of job tasks in a clinical setting can provide valuable information concerning ability to return to work,43–46 especially when the physical requirements of the job are substantially different from the work performed during an ET. Monitoring should include continuous ECG telemetry, intermittent blood pressure determinations, and assessment of symptoms.
The first step in assessing simulated job tasks is to identify job-related tasks that are agreed to by the patient, management, and, if appropriate, the union. The simulation of job tasks should include specific information related to the performance of each PA. For example, if the task is lifting and carrying, the information should include the minimum and maximum weight to be lifted, the height of lifting, and the distance walked while carrying. A standardized weight-carrying and weight-lifting test protocol46,47 or 1 customized to reflect specific job tasks can be used. Compared to handgrip testing, weight-carrying resulted in significantly higher heart rate, systolic blood pressure, rate-pressure product, ventilation, and
O2 in patients with coronary heart disease.48
Most assessments can be conducted using existing equipment or purchasing inexpensive additional equipment (eg, adjustable shelving unit, crates to hold free weights). A significantly more sophisticated and expensive approach involves the use of specialized work simulators, such as the Simulator II (BTE Technologies, Inc, Hanover, Maryland), that can expand the range of the simulated testing. Simulated job task testing does not account for psychological or environmental stress that may be encountered by the patient on the job. Occupational therapists can provide valuable additional expertise for this type of testing.
Continuous ECG monitoring and intermittent blood pressure determinations can provide documentation of myocardial ischemia, cardiac dysrhythmias, and hypotensive or hypertensive episodes that may be elicited by the job task simulation. The equipment necessary for this monitoring is readily available in outpatient CR facilities. Occupational therapists can provide additional expertise for simulated job task assessments.
ROLE OF CARDIAC REHABILITATION IN IMPROVING FUNCTIONAL CAPACITY
Since its origins in the 1950s, the aim of CR services has been to assess, manage, and reverse disability in patients with cardiac conditions49,50 and these remain pertinent and important today. Research has shown that CR is safe and effective, resulting in multiple significant patient benefits, including improvements in all-cause mortality, cardiac morbidity, physical work capacity, return to work, control of CVD risk factors, and quality of life.51–55
Cardiac rehabilitation is indicated for 6 specific groups of patients: myocardial infarction, percutaneous coronary intervention, coronary artery bypass graft surgery, chronic stable angina, heart valve surgery, and/or heart transplantation. While evidence suggests benefits of CR for patients with heart failure and with peripheral arterial disease, these conditions are not currently included in the Centers for Medicare & Medicaid Services indications for CR but are included in selected clinical guidelines.51 Less is known about the impact of CR in patients with other CV conditions associated with CV disability, such as high-grade arrhythmias, hypertrophic cardiomyopathy, or congenital heart disease.
Disability in patients with a recent cardiac event is significant and relatively common. The average exercise capacity for patients entering a CR program was only 4 METs and 5.5 METs in women and men, respectively, which approaches levels seen in patients with heart failure and is consistent with CV disability.56 Cardiac rehabilitation can increase aerobic exercise capacity by 20% to 30%, with the greatest increase in patients who are the most disabled at entry.53,57 If a disability assessment was performed prior to a patient completing CR, a subsequent second assessment should be completed.
Several key steps can help maximize the role of CR programs in the assessment, treatment, and reversal of CV disability:
- Train CR staff about key components of CV disability assessment and treatment strategies that reduce CV disability.
- Include activities in CR that simulate work conditions, specific to job-related responsibilities, in patient assessment and treatment plans.58
- Measure impact and outcomes of cardiac disability assessment and treatment program services, relative to patient physical work capacity, psychological health, and return to work.
- Provide education and communications to local providers regarding the need for and availability of cardiac disability assessment and treatment services provided through the local CR program.
SUMMARY AND FUTURE DIRECTIONS
The deliberations of the IOM Committee to Revise the Criteria for Cardiovascular Disability in its Listing of Impairments sought to identify tests or procedures that would quantify functional capacity, which would be generally available either in the claimant medical record or for purchase for the assessment of potential claimants. Highlighted in the Committee report2 was the lack of consistent relationship between the CV anatomic alterations and resultant functional capacity; hence, delineating the anatomy should be used solely to define the presence and severity of disease, but the disability process requires additional information on the functional limitations imposed by the disease. Cardiac rehabilitation facilities offer a unique resource for functional assessment for disability determination, given the availability of test procedures and the trained skilled personnel accustomed to interaction with individuals with CVD. Not related specifically to the SSD process, but relevant to the national public CV health and occupational requirements, are issues of work assessment, recommendations for work modification, and specific CV exercise training—all of which should contribute to an enhanced opportunity for individuals with CVD to appropriately return to the workforce. The resulting monograph addresses in succinct summary the validated and available test procedures and thus constitutes a valuable resource for clinicians and for the SSA.
The IOM Committee further addressed future directions for improving the Listings. Policy issues involve the potential of health insurance reform to increase access to CV health services, including tests and procedures that could be used to meet or revise the Listings. In addition, increased access to health services may reduce the decline in an individual's CV health and the resultant inability to work. Social Security Administration should support research on the disability-related effects of health insurance reform to improve program planning and future updates of the Listings.
It would appear to be cost-effective to conduct research to validate the Listings, both at SSA and externally, with a full and balanced program of research addressing policy implications, programmatic issues, correlation of CV impairments and impairment severity with functional limitations related to work capacity, and the underlying prevalence of trends in CV impairments in the population.
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Keywords:© 2013 Lippincott Williams & Wilkins, Inc.
cardiac rehabilitation; cardiovascular disability; functional capacity assessment; social security disability