Levels or Types of Measurements

Measurements can be described according to their type or level of measurement. There are four levels of measurements: nominal, ordinal, interval, and ratio (Table 7-1).² Recognizing the level of measurement aids understanding and interpretation of the result.

Reliability and Validity of Measurements

For a measurement to be of value to the therapist, the measure should be both reliable (reproducible) and valid (meaningful). When selecting and performing tests and measures, it is important to remember that measures can be reliable but not valid for a specific application.⁷

Sensitivity and Specificity

Accuracy of various types of exercise tests often is described by reporting sensitivity and specificity. Sensitivity is the ability of a measurement to identify individuals who are positive, or who have the characteristic that is being measured. If a test produces a high number of false-positive results, then the sensitivity will be low. A false-positive result means that the test result was positive but the characteristic was absent. Young women often have positive stress test results but do not have coronary artery disease. The consequence of a false-positive test result could be unnecessary treatment or further diagnostic testing. Specificity is the ability of a measurement to identify individuals who are negative, or who do not have the characteristic. A high number of false-negative results would produce a low specificity. A false-negative result has a negative test result even though the disease or characteristic is present. The consequence of a false-negative test result is not receiving treatment when it is indicated. Use of the Homans’ sign to screen for deep vein thrombosis (DVT) is no longer advocated because the test lacks both sensitivity and specificity.11,12

Objective and Subjective Measurements

Measurements vary in degree of subjectivity versus objectivity. Subjective measurements are those that are affected in some way by the person obtaining the measurement (i.e., the measurer must make a judgment as to the value assigned). The assessment of a patient’s breath sounds is influenced by many factors, including the therapist’s choice of terminology for describing the findings, perception of normal breath sounds, and hearing acuity. The grading of functional skills may be influenced by the therapist’s interpretation of what constitutes minimal versus moderate assistance. Because of the influence of the person performing the measure, subjective measurements usually have lower interrater reliability compared with objective measurements.²

Objective measurements are not affected by the person performing the measure (i.e., these measures do not involve judgment of the measurer). Heart rate measured by a computerized ECG system is an example of an objective measurement. Other examples include measuring blood pressure using an intraarterial catheter and oxygen consumption using a metabolic system. Objective measurements are not necessarily accurate but usually have high interrater reliability.²

Clinical Decision Making

The Hypothesis-Oriented Algorithm for Clinicians II (HOAC-II) intertwines the examination, evaluation, and diagnosis elements into an organized algorithm for clinical decision making.¹³ Using the HOAC-II, initial data collection (e.g., data from the medical record and patient interview) during the examination allows for generation of patient-identified problems (PIPs) and an initial set of hypotheses that will guide the formulation of an examination strategy (i.e., selection and ordering of tests and measures). These initial measurements help refine the hypotheses and additional measurements are obtained to help confirm or deny the initial set of hypotheses, leading to an eventual hypothesis/physical therapy diagnosis (i.e., an idea of the underlying cause of the patient’s problem), and/or a decision to consult with other health care practitioners. For instance, early in the examination process the therapist may suspect a proximal DVT; the Wells clinical decision rule can aid in deciding whether or not to refer the patient for further testing.¹⁴

Examination

Initial data collection from referral information or the medical record regarding the patient’s current medical stability and functional status will help guide the examination strategy. For example, tests and measures will differ for a patient with an acute MI compared to a patient who is 3 weeks post-MI. Other factors to consider include the size of the infarction and associated complications such as dysrhythmias, heart failure, or angina. Other initial data collected during the interview may also guide the examination strategy. For example, if a patient becomes anxious when discussing walking on a treadmill, then perhaps a “field test,” such as the 6-minute walk test (6-MWT), would be more prudent.

The examination begins with and is centered on the patient’s self-identified problems that may reflect specific impairments, limitations in activity, and/or restrictions in patient-identified roles at home, work, and the community. The patient’s goals for physical therapy should be reported. Documentation of examination findings should reflect the physical therapist’s clinical reasoning in determining what impairments may underlie the patient’s limitation in activity.

The history section may include information related to the current and past medical/surgical diagnoses, previous functional levels, lifestyle choices, living environment, medications, laboratory values, or diagnostic imaging results. The patient’s perception of his or her cardiac or pulmonary condition is important, as are descriptions of pain or discomfort that may be associated with either a cardiac event or a pulmonary complication. Other systems, such as the musculoskeletal, neurological, and integumentary systems are briefly examined to identify concerns that may influence the patient’s readiness or ability to participate in certain interventions.

Tests can be categorized as measuring impairments, activity limitations, or participation restrictions as defined by the World Health Organization’s International Classification of Functioning, Disability and Health (ICF) model,¹⁸ which was recently adopted by the American Physical Therapy Association (APTA).¹⁹ A body function or body structure impairment is an abnormality of physiological function or anatomic structure at the tissue, organ, or body system level.¹⁵ Examples of impairments include pain, dyspnea, decreased muscle strength or range of motion, abnormal heart rate and blood pressure values, and impaired aerobic capacity. Measurements of impairments are important because they assist therapists in deciphering the causes or reasons for limitations in activity. Activity limitations are difficulties an individual has in performing a task or action.¹⁵ Activity limitations can be attributed to physical, social, cognitive, or emotional factors. Examples of activity limitations include the inability to dress, transfer, walk long distances, or climb stairs. Improvements in activity levels usually are of primary interest to patients and families and to those who reimburse for health care. Participation restrictions are those problems that an individual may experience in life situations, such as performing a job requirement or playing a sport.¹⁵ Figure 7-1 illustrates a patient’s condition using the ICF model.

When examining patients with cardiopulmonary disorders, therapists often assess responses to activity. Specific information on the activity and on the physiological responses should be included:

The description of activities should be written clearly so that the workload can be reproduced. Responses to activity include changes in heart rate and rhythm, blood pressure, respiratory rate, oxygen saturation levels, and heart and breath sounds from pre-activity to either during or immediately after activity. Subjective signs of exercise intolerance, such as changes in skin color, decrease in coordination, and sweating, also need to be documented. Whether the patient used oxygen during treatment or required physical assistance should be noted. By objectively recording the activity performed and the physiological responses, therapists can estimate the patient’s activity tolerance.

Evaluation and Interpretation of Findings

The evaluation process involves using the results of the examination to make clinical judgments. Therapists state their “clinical hypothesis,” or explanation of reasons for activity limitations and/or participation restrictions. Evaluation reports provide the foundational support to confirm why the patient requires the skilled services of a physical therapist and why the services are medically necessary at this time. Examination findings may indicate the need for referral of the patient to other health care professionals or to community services.

Interpreting measurements often is challenging. Usually patients’ problems are understood not by reviewing results of a single measure but by viewing relationships between results of several measures. For example, the finding that blood pressure does not increase with activity may not be considered abnormal by itself if the activity level is low or the patient is taking a beta-receptor antagonist medication (e.g., metoprolol); however, the finding of no increase in blood pressure with signs and symptoms of exercise intolerance (e.g., shortness of breath, dizziness, fatigue, etc.) during moderate-level activity in another patient may be indicative of cardiovascular pump dysfunction.

Knowledge of what is “normal” is important to interpret measurements accurately. For some measurements, normal values are well defined. Measurements of resting blood pressure, cholesterol, and blood glucose have defined categories of normal, borderline, and elevated. For other measurements, population normative standards are not specifically defined. For example, what is the normal increase in heart rate when walking at 3.5 mph on a level surface? Values for individuals differ depending on age, medications, fitness level, and walking efficiency. Results must be interpreted by considering these factors and pathological conditions, if present. Each individual has his or her own “normal” or usual response, and variations from this value could be considered abnormal.

Interpreting measurements is similar to putting the pieces of a puzzle together to create a picture of the patient and his or her activity limitations and participation restrictions. Data are collected from several sources, including the medical record, patient interview, and physical therapy examination. Measures performed and interpreted by other health care professionals can be obtained from the medical record; these include measures such as chest radiographs, blood tests, echocardiography, angiography, and ventilation-perfusion scans. During an interview, patients report information about their current and past medical problems and especially specific patient-identified problems. It is important to be sensitive to patient’s feelings about their condition, noting their stage of emotional recovery. Detecting attitudes related to changing lifestyle habits is also important. After the interview, the therapist should have a sense of the patient as a person and begin to plan an intervention strategy for improving body structure and function impairments, and optimizing activity and participation.¹³

Measures made during the physical examination may include physiological responses to activity, breathing patterns, ventilatory capacity, and breath sounds. These measurements are integrated with results collected during the chart review and evaluated in the context of the patient-identified problems and the goals for each problem. As therapists refine their hypothesis, they develop a picture of the severity of the cardiopulmonary condition, stage of recovery, and presence of coexisting conditions. An intervention strategy is developed on the basis of the final clinical hypothesis/diagnosis. The intervention strategy is implemented, and measurements are regularly obtained during treatment sessions to reassess existing problems and goals. Because of the dynamic nature of many of the conditions that affect the cardiovascular and pulmonary systems, each treatment session can be viewed as a reassessment of the hypothesis and progress toward patient goals.

Minimal Clinically Important Difference

To help facilitate evidence-based practice related to interpreting outcome measurements, a minimal clinically important difference (MCID)—that is, “the minimal level of change required in response to an intervention before the outcome would be considered worthwhile in terms of a patient/client’s function or quality of life”²⁰—has been determined for several endurance/aerobic capacity tests and measures used by physical therapists. Examples include the 6-MWT (54 m²¹ or 10% improvement²²), modified shuttle test (40 m²³), and the Borg CR10⁴ and visual analog scale ratings of dyspnea (1 point and 10-20 mm [Table 7-3], respectively²⁴). The MCID for various tests and measures can be used for setting relevant goals, as well as interpreting progress toward outcomes.

Physical Therapy Diagnosis, Prognosis, and Plan of Care

The physical therapy diagnosis serves to drive the selection of interventions. A physical therapy diagnosis may be written in the form of a problem list that may include both impairments and activity limitations. Problems can be listed in order of priority and stated in functional terms. For example, stating “patient unable to climb stairs because of abnormal ECG responses and dizziness,” rather than “abnormal ECG response during activity” is recommended. Alternatively, physical therapy–related classification systems such as the Practice Patterns found in the Guide to Physical Therapist Practice²⁵ may be tailored to reflect the individual’s physical therapy diagnosis.

Based on the results from a 6-MWT, or another appropriate test, a tentative physical therapy diagnosis of impaired aerobic capacity/endurance impairment could be made if the measurement falls outside the reference values for healthy adults.²⁶ Concurrent or complementary measures (e.g., respiratory rate, heart rate and blood pressure response, pulse oximetry, heart and lung sounds, ankle brachial index) could help further refine the hypothesis and determine whether the impaired endurance was more likely due to cardiac, peripheral vascular, or pulmonary impairments.

After identifying the patient’s problems and determining a diagnosis for physical therapy, a plan of care that includes prognosis is developed. The plan of care includes goals and anticipated outcomes, specific interventions to be used, and the recommended frequency and duration of the interventions. The prognosis is the predicted level of improvement and the amount of time needed to reach that level. Providing additional data related to positive and/or negative contextual factors to justify prognosis is important to reinforce the skilled nature of services. Positive factors may include family support, previous functional levels, or the acuity of the condition. Negative factors may include the severity or chronicity of the condition, barriers in living environments, or lack of financial resources.

Goals are the outcomes to be achieved by participating in a physical therapy program and are generated by the therapist and patient in collaboration. Goals should have baseline measurements documented from the examination, be related to the identified problems, and be supported by statements in the evaluation section. Goals should highlight cardiovascular and pulmonary impairments that are thought to be linked to the activity limitations. Goals are stated in functional terms and concern what the patient will be able to do at discharge. For example, a goal could be “patient will be able to walk up two flights of stairs with appropriate heart rate and rhythm responses, within 2 weeks.” Without documenting the associated cardiovascular and pulmonary impairments, the goal may not support the individual’s need for skilled or medically necessary services by physical therapy.

To determine whether a goal has been met, the therapist must be able to observe or measure the activity. Therapists also estimate the time it will take to achieve the outcome. In a discharge or follow-up note, it is stated whether each goal has been met. If a goal has not been achieved, an explanation is provided.

The plan provides a description of the approach that will be taken to assist the patient in achieving the stated goals. The plan may include a description of treatment that can be provided, education for the patient and/or family, and referrals to other services. Descriptions of inpatient, outpatient, or home programs should be included in the plan. The plan of care also includes discharge planning.

Intervention

Interventions are physical therapy procedures and techniques designed to produce changes in the patient’s condition. Procedures typically used by therapists treating patients with cardiopulmonary disorders include therapeutic exercise (i.e., aerobic, resistance, breathing exercises), functional training (i.e., work hardening and work conditioning), and airway clearance techniques. The specific intervention selected by the therapist will be influenced by the severity of the cardiopulmonary disorder and the presence of complications. In some cases, the intervention mode and intensity can be derived from the measurement obtained. For instance, 6-MWD can predict peak VO₂ in patients with COPD²⁷ and heart failure;²⁸ with this predicted value, converted to METs, the physical therapist can develop an appropriate exercise prescription and guide the patient in selecting physical activities that would fall within a safe and therapeutic range. In addition, a treadmill or overground walking program could be established on the basis of the mean walking velocity during the 6-MWT.²⁹ Likewise, physical activity/exercise intensity could be set based on measurements of perceived exertion or dyspnea obtained during an exercise test.

Patient and family and/or caregiver instruction is part of all physical therapy interventions. Communication with other health care disciplines involved in the patient’s care is essential to ensure efficient and effective health care. For example, for a patient who is being discharged from the hospital after cardiac surgery, the therapist may need to coordinate with the social worker to ensure that the patient receives home services that he or she needs for assistance with activities of daily living.

Documentation is an essential part of intervention. It is important to record the patient’s responses to interventions, including changes in heart rate, blood pressure, and heart and lung sounds, recovery time after exercise, and reports of angina, dyspnea, or fatigue. A description of the intervention is recorded so that another therapist or physical therapist assistant can continue the program. Details related to dosage, such as frequency, intensity, and duration of each intervention should be clearly stated. In addition to the medical record, the therapist also may be required to provide documentation to other sources such as home health or insurance agencies.

Reexamination and Outcomes Assessment

Throughout the course of treatments, therapists routinely perform reexaminations to determine whether patients are progressing. For patients with cardiopulmonary disorders, for example, the therapist may reexamine the patient at every session to determine whether physiological responses to activity are appropriate or whether the patient’s lungs are clearing. Results of reexamination are used to modify or redirect interventions. It is important to include documentation of patient progression, including the patient’s perception of progression, in each note in order to support the continued justification of skilled services.

As the patient approaches discharge from physical therapy services, the therapist assesses the outcomes of the intervention. The therapist measures the impact of physical therapy services on the patient’s impairments, activity limitations, and participation restrictions. Examples of outcome measures often used to assess health-related quality of life in patients with cardiopulmonary disorders include the Chronic Respiratory Questionnaire³⁰ and Minnesota Living with Heart Failure questionnaire.³¹

The therapist relates the assessment of outcomes to the original goals established by the therapist and patient. As a result of the outcomes assessment, the therapist may refer the patient back to the physician or to another health care professional. A systematic review of medical records from a group of patients with similar diagnoses can be performed to determine program outcomes of selected physical therapy interventions. See Chapter 17 for a discussion of optimizing outcomes.