Dyspnea is 1 of the most common and debilitating heart failure (HF) symptoms and is associated with a high level of distress,1,21,2 decreased functional capacity,1 and lower quality of life.3,43,4 Among patients with HF, acute dyspnea is the most common cause of urgent medical care and hospital readmission.5 Importantly, in ambulatory patients with HF, dyspnea may be a sign of worsening or undertreated HF. Consequently, the evaluation of dyspnea is part of the routine clinical examination of the ambulatory patient with HF.
Different dyspnea measurement instruments have been used in ambulatory patients with HF to evaluate the effects of pharmacologic6,76,7 and exercise8,98,9 interventions. There are many validated dyspnea instruments; however, there is no standardized protocol for the measurement of dyspnea in stable ambulatory patients with HF with respect to the type of dyspnea instrument, timing (real-time or recall), and/or condition (rest, exercise, or patient position).10,1110,11 All these considerations are important because they may affect the accuracy of the patients’ responses. In addition, depending on the instruments, different dimensions of dyspnea may be measured, including sensory-perceptual experiences (what breathing feels like to the patient), affective distress (the unpleasantness or distress associated with dyspnea), and symptom impact or burden (how dyspnea affects functional ability or quality of life).1,111,11
Dyspnea instruments have also been qualified as unidimensional or multidimensional. Unidimensional dyspnea instruments, such as the modified Borg scale or visual analog scale (VAS), measure the sensory component or severity of dyspnea. These instruments are a single item rating of intensity and measure what breathing “feels like” to the patient at a single moment or averaged over a period.11 An advantage of unidimensional instruments is that they are short and simple for the patient to complete. Unidimensional instruments have been extensively used in cardiopulmonary exercise testing and research.12 Multidimensional instruments are often disease specific, measuring domains related to physical, psychosocial, or quality of life, and help in determining how symptoms and other variables might relate or cluster together. Examples of multidimensional instruments include the Chronic Heart Failure Questionnaire4 and the Memorial Symptom Assessment Scale Heart Failure.15 These multi-item instruments may require 30 minutes or more to complete.
Most HF studies evaluating dyspnea in the ambulatory setting have predominately enrolled patients with reduced ejection fraction (HFrEF) and excluded those with HF with preserved ejection fraction (HFpEF; ejection fraction >50%).3,4,6,93,4,6,93,4,6,93,4,6,9 More than half of all patients with HF have a preserved ejection fraction.16,1716,17 In addition, HFpEF may be more common among African American patients with HF. Gupta et al18 found that in a community-based cohort of African Americans with HF (n = 116), HFpEF was the predominant type of HF.
In general, there is a paucity of data regarding the prevalence and intensity of dyspnea in HFpEF,19,2019,20 with few studies enrolling AAs. Consequently, we studied dyspnea exclusively in AA patients and included those with HFpEF. Patients with HFpEF have a limited cardiac reserve and, accordingly, are more likely to experience dyspnea with physical activity.21,2221,22 Therefore, using some form of activity may be an important strategy to evaluate dyspnea in this population. On the basis of the literature, we hypothesized that using the 6-minute walk test (6MWT) would provide an adequate stimulus to provoke dyspnea in both HF groups.
The purpose of this study was to examine dyspnea in AAs with HFpEF compared with those with HFrEF. The specific objectives were to (1) determine and compare the prevalence of dyspnea before and after the 6MWT, (2) compare the intensity of dyspnea and level of agreement before and after the 6MWT as measured by the Borg and VAS, and (3) describe patient-reported activity limitations using the modified Medical Research Council Dyspnea Scale in both groups. Understanding the prevalence and measuring the intensity of dyspnea is important among stable ambulatory AA patients with HF, considering their high level of HF prevalence, younger age at HF onset, and high mortality rates in order to develop effective treatment strategies.23
Design, Sample, and Setting
This was a cross-sectional study enrolling a convenience sample of AAs 50 years or older with HFpEF (n = 19) or HFrEF (n = 26) recruited from an urban university cardiology outpatient clinic between December 2012 and February 2013. Inclusion criteria were as follows: (a) diagnosis of HFpEF (EF ≥50%)24 and elevated left atrial pressure or HFrEF (EF <40%),25 as determined by 2-dimensional echocardiography26; (b) New York Heart Association functional classification I to III at enrollment; (c) ability to walk without the use of a cane or portable oxygen; and (d) optimal guideline-directed HF therapy for 3 months before study enrollment.27 Exclusion criteria were as follows: (a) primary valvular and congenital heart disease, (b) heart transplantation, (c) obstructive cardiomyopathy, (d) cardiovascular event or procedure within the past month, (e) defibrillator and/or resynchronization implantation within 3 months, (f) hemoglobin A1C level greater than 9.0, (g) systolic blood pressure greater than 180 mm Hg and/or diastolic blood pressure greater than 100 mm Hg on 2 consecutive readings, (h) resting heart rate greater than 120 bpm, (i) pulmonary artery pressure greater than 55 mm Hg as determined by echocardiography, or (j) new-onset atrial fibrillation. These criteria were chosen to exclude patients with multiple comorbid conditions and potential confounding causes of dyspnea and to adhere to the recommendations outlined in the American Thoracic Society (ATS) 6MWT protocol.28 In addition, those with an EF of 40% to 50% were excluded to clearly delineate HFpEF and HFrEF patients.
Sample size was estimated a priori using a power analysis (G-power version 3.1.3, Univeristat Dusseldorf, Germany) to determine the number of participants needed to detect a significant difference in dyspnea scores between HF groups and pretest versus posttest scores. The expected effect size (ES) was derived from a previously published study that measured dyspnea scores using the Borg scale in response to an exercise program in patients with HFrEF (ES, −0.46; N = 40).9 Sixty participants were needed for 80% power to detect differences in dyspnea scores with a 2-sided test and a moderate ES (d = 0.5) (HFpEF, n = 30; HFrEF, n = 30).
Modified Borg Scale
The Modified Borg Dyspnea Scale (Borg) is a valid and reliable instrument widely used to evaluate dyspnea intensity in healthy and cardiopulmonary populations in diagnostic testing and activity research13,28,2913,28,2913,28,29 and is recommended by the ATS for this purpose.28 The modified version is a 12-point numerical rating scale with incremental increases from 0 (no dyspnea) to 10 (maximal dyspnea).The first increment is 0.5, followed by 1-point increases thereafter. The minimally clinically important difference (MCID) for the Borg scale in patients with chronic HF is a 1-point change.25 The Borg was administered before and after completion of the 6MWT. Dyspnea was monitored during the 6MWT per the ATS protocol.28
Visual Analog Scale
The VAS, a valid and reliable measure of self-reported dyspnea intensity,31 has been used to track changes in dyspnea over time in patients with acute HF (AHF).5,32,335,32,335,32,33 The VAS consists of a 100-mm vertical line calibrated in 10-mm segments, bounded by the descriptors “no shortness of breath” at 100 and “worst shortness of breath” at 0,32,3332,33 with consensus indicating the MCID to be approximately 20 mm.34,3534,35 In a predominantly AA cohort of patients with AHF, Ander and colleagues34 reported that a change of greater than 21 mm represented an MCID with the VAS. In our study, the VAS was administered as a paper-and-pencil test and was administered before and after the completion of the 6MWT.
Medical Research Council Dyspnea Scale
Because patients with HFpEF may be more likely to experience dyspnea with activity, we used the Medical Research Council Dyspnea Scale to quantify and describe patient-reported dyspnea-associated activities. The MRC has been validated in pulmonary patients and allows patients to select daily physical activities that precipitate dyspnea.36 Patients select 1 of 5 descriptive statements that correspond to a “grade” ranging from grade 0 = “not troubled by breathlessness except on strenuous exercise” to grade 4 = “I am too breathless to leave the house or breathless when dressing or undressing.” A higher grade indicates greater activity limitations. Others have shown that patient-reported MRC responses are not sensitive to change over short periods or certain interventions but correlate to 6-minute walk (6MW) distance.37 Therefore, the MRC instrument was administered only once and before the 6MWT.
6-Minute Walk Test
The 6MWT was used as a measure of activity tolerance and to provoke dyspnea. The 6MWT has been shown to be reliable, with moderate to strong correlations with maximal exercise capacity in patients with HF.38,3938,39 Patients performed the 6MWT according to the ATS protocol guidelines.28
Before the 6MWT (defined as baseline) and while in a sitting position for 15 minutes, patients completed the MRC, Borg, and VAS (order of administration randomly assigned). During the 6MWT, the Borg was completed at 1-minute intervals (patients verbally reported their Borg score). After the 6MWT, patients returned to an upright sitting position and were readministered the VAS. All unidimensional dyspnea instruments were used to limit the subject burden. The protocol was approved by the Institutional Review Board of the University of Illinois.
Independent t tests, χ2 tests, and Fisher exact tests were used to determine differences in sample characteristics and demographics. Patients were classified as having no dyspnea (0 on the Borg scale or 100 on the VAS) or having dyspnea (≥0.05 on the Borg scale or <100 on the VAS), and χ2 tests were used to determine the prevalence and intensity of dyspnea at baseline and after the 6MWT. Numerical dyspnea scores were analyzed using analysis of variance (2-way repeated-measures analysis of variance) to test for within-group (pretest vs posttest) and between-group (HFpEF vs HFrEF) differences. Analyses were performed using SPSS 20 statistical software (Chicago, Illinois). All tests were 2 sided, and P < .05 was considered statistically significant.
Bland-Altman plots were generated using SAS (version 9.2) to determine the convergent validity or agreement between the Borg scale and VAS scores at baseline and after the 6MWT test. Unlike scatter plots, Bland-Altman plots display individual variation along a range of scores. To compare the 2 scales, the VAS scores were converted to a scale of 0 to 10 (VAS score divided by 10, with 10 representing maximal dyspnea and 0 representing no dyspnea). A range of agreement was defined as mean bias ± 2 SD.40,4140,41
No differences were found between HF groups in age, HF etiology (ischemic vs nonischemic), blood pressure, or incidence of atrial fibrillation (Table 1). Approximately half of the sample was female (n = 45; 53%). All patients had a history of hypertension, which varied in duration from 2 to 21 years. Most patients in both groups had a body mass index greater than 25 kg/m2 (Table 1). All patients with HFrEF were prescribed an angiotensin-converting enzyme inhibitor, whereas patients with HFpEF were more likely to be prescribed calcium channel blockers (χ2 = 11.34, P = .001; χ2 = 5.46, P = .019, respectively; Table 2). Other medication use was similar (Table 2).
In the HFpEF group, no differences were found in the percentage of patients (>60%) reporting dyspnea before or after the 6MWT test using the Borg and VAS (Table 3). In contrast, there was a significant difference in the prevalence of dyspnea reported using the VAS compared with the Borg (80% vs 35%, respectively, P < .001) within the HFrEF group at baseline. However, after the 6MWT, the percentage of HFrEF reporting dyspnea with the VAS (77%) and Borg (65%) was not different. At baseline and after the 6MWT, the prevalence of dyspnea was not significantly different between the HF groups as reported on the Borg or VAS (Table 3, P > .05).
Dyspnea Intensity at Baseline and After the 6-Minute Walk Test
Modified Borg Scale
Both groups reported dyspnea scores that were statistically significant for within-group differences from baseline to 6 minutes (P < .01, Table 4). There were progressive increases in Borg scores during the 6MWT, and the magnitude of change was similar between HF groups. For both groups, of the 36 patients who reported increasing dyspnea, most (66%, n = 22) reported their highest Borg score at 6 minutes. In both groups, the change in the Borg score from baseline to after 6MWT was clinically significant (mean ± SEM difference, HFpEF: −1.30 ± 0.53; HFrEF: −1.50 ± 0.43).
Visual Analog Scale
In both HF groups, no change was found between scores at baseline and after the 6MWT VAS. There was a significant between-group difference in the VAS scores, with the HFrEF group reporting more dyspnea after the 6MWT (F = 14.94, P < .017). In both groups, the change in the VAS score from baseline to after the 6MWT was not clinically significant (<20 mm change) from baseline.
The correlations between the Borg scale and VAS were determined for the combined HF sample (n = 45) and separately for each HF group at 2 time points: baseline and after the 6MWT. Scores at baseline correlated significantly for all patients (n = 45, r = −0.473, P = .001) and for the HFrEF group (n = 26; r = −0.597; P = .001) but not the HFpEF group (n = 19; r = −0.311; P = .195). Analysis of the scores after the 6MWT showed a significant correlation for all patients (n = 45; r = −0.460; P = .001) and for each HF group (HFpEF, n = 26; r = −0.394; P = .047; HFrEF, n = 19; r = −0.575; P = .010).
Bland-Altman plots were constructed to determine if the agreement between the Borg and VAS scores differed at baseline and after the 6MWT (Figure 1A and B, respectively). The average of the difference (bias) between the baseline Borg and VAS scores was −1 (solid horizontal line). This indicates that patients reported consistently lower resting Borg scores compared with VAS scores. The dotted lines represent the 95% confidence interval for the difference between the 2 measures, which ranged from −5 to 3. Examination of the data points over and under the 95% confidence interval suggested that discrepancies from the mean increased as the average of the 2 measures increased. Overall, evidence for the agreement between the 2 instruments at baseline was moderate.
The average of the difference (bias) between Borg and VAS (Borg-VAS) scores after the 6MWT approximated 1 (solid horizontal line), indicating that patients reported consistently higher scores using the Borg scale compared with the VAS. The 95% confidence limits for the average Borg-VAS difference ranged from −4 to 5. Agreement between the 2 measures after the 6MWT was moderate.
Medical Respiratory Council Dyspnea Grade
Both groups reported the full range (0–4) of MRC grades (Figure 2). Approximately half (46.2%, n = 12) of the HFrEF patients selected grade 1 (hurrying or walking up a slight hill) as the activity most likely to be associated with dyspnea. In the HFpEF group, an equal number of patients (31.6%, n = 6) selected grade 1 or 3 (walking 100 yards or a few minutes on a level surface, respectively) as most likely to be associated with dyspnea. The differences among the proportion of the MRC grades (0–4) by HF type were not significant (ranked χ2 = 0.58; P = .445). In both groups, most patients indicated that walking (ie, MRC grade 1, hurrying, walking up a slight hill, or grade 3, walking 100 yards or for a few minutes) would most likely provoke dyspnea, and MRC grades were inversely correlated to the 6MW distance (HFpEF, 215.55 ± 18.65; HFrEF, 226.85 ± 15.32) for each group (HFpEF, r = −0.64, P < .01; HFrEF, r = −0.59, P < .01).
The prevalence of dyspnea was high at baseline and after the 6MWT for both groups of patients. In the HFpEF group, dyspnea ratings at baseline and after the 6MWT were similar regardless of whether the Borg or VAS was used. However, fewer in the HFrEF group reported dyspnea at baseline using the Borg compared with the VAS. The increase in the intensity of dyspnea after the 6MWT was similar between groups and was clinically significant for the Borg. Most HFpEF and HFrEF patients self-reported walking hurriedly uphill (grade 1) or walking for a few minutes (grade 3) as dyspnea-associated activities on the MRC scale.
Dyspnea prevalence was greater than 60% in HFpEF patients and varied between 35% (Borg scale) and 80% (VAS) in HFrEF patients. Others have reported a wide range of dyspnea prevalence rates (26%–85%) among HF patients.2–4,372–4,372–4,372–4,37 The wide range in prevalence rates may relate to differences among studies in sample characteristics (severity of HF and presence of comorbidities) and attributes of the instruments. For example, some instruments require patients to rate their dyspnea over the past week versus a single time point. Notably, studies reporting higher prevalence (56%–85%) most often used a multidimensional instrument, and patients with pulmonary comorbidities were included.2–42–42–4 It is possible that HF status may affect dyspnea prevalence; however, findings related to HF status and dyspnea prevalence are equivocal. Using a multidimensional instrument, Blinderman et al2 reported dyspnea prevalence rates of 56.3% (N = 103) in end-stage (New York Heart Association II–IV) HF patients with EFs of 22% to 23%, whereas Naylor and colleagues,42 using the Borg scale, reported dyspnea prevalence rates of 26% (N = 31) in ambulatory patients with HF (EF <35%). In the Naylor et al study, patients with chronic obstructive pulmonary disease were excluded. In our study, we used unidimensional instruments, excluded patients with elevated pulmonary pressures, but included those with a history of chronic obstructive pulmonary disease. Before the 6MWT, using the Borg, baseline dyspnea prevalence was 35% in the HFrEF group, whereas using the VAS, dyspnea prevalence was 81%. However, this discrepancy narrowed after the 6MWT (Borg, 65% vs VAS, 77%). It is unknown why there was a discrepancy in the estimation of baseline dyspnea prevalence between the Borg and VAS in the HFrEF group because both are unidimensional and patient-reported dyspnea instruments.
Others have also reported that HFrEF patients with AHF reported higher scores with the VAS at baseline compared with Likert scales.43 In young, healthy male adults using similar submaximal exercise conditions, Grant et al44 compared the VAS, Borg, and Likert scales. The investigators also found higher VAS scores at baseline. The VAS was more reproducible over a 4-week period compared with the Borg and Likert scales.44 Grant et al44 defined “reproducibility” as the proportion of total variance (ie, between-subject plus within-subject variance) explained by the between-subject variance, given as a percentage. Interestingly, in our study, the HFpEF group prevalence rates measured using the Borg and VAS were similar.
It remains unknown which dyspnea instruments are most reliable and responsive to changes in the intensity of dyspnea in HF during activity.10 However, the Borg scale has been used extensively to evaluate dyspnea during cardiopulmonary exercise testing.28 Similar to others, we defined the MCID for the Borg scale as a change greater than 1 point and for the VAS a 20-mm change.27,2827,28 In our study, the Borg scale was able to detect significant statistical and clinical (MCID) changes in dyspnea before and after the 6MWT. The Borg scale was easy to administer during activity and provided clinically relevant information. The VAS took longer to complete and could not be administered during activity. Others have suggested that the greater number of scoring levels with the VAS may contribute to increased intersubject variation.45 The baseline scores between the Borg and VAS were discordant in the HFrEF group and not the HFpEF group; it is difficult to speculate why we found this difference. Some patients may have had difficulty or felt uncomfortable using the VAS when it was first administered. However, the Bland-Altman plots, which were used to provide a visual understanding of our findings, indicated that the agreement between the Borg and VAS was moderate at both time points, with less agreement at baseline and greater variability as dyspnea intensity increased. The variation in response is not surprising because the patients’ perception of dyspnea may be influenced by previous experiences with dyspnea and their ability to “work through” their dyspnea.34
As expected and similar to others, we found that the MRC grades were inversely correlated to the 6MW distance. This finding validates that the 6MWT was an effective method for provoking dyspnea in patients with HFrEF and HFpEF. Future HF studies using the MRC may help to determine if the MRC grade, in conjunction with other measures, can be used to predict or monitor the impact of dyspnea on functional outcomes.
Given the importance of dyspnea and its association with poor outcomes, further study of how to best measure dyspnea is warranted. This is especially important for AAs with HF who develop HF at a younger age; these patients have not been represented in many HF trials. The current literature suggests that the progression of HF in AAs may be characterized by predominantly nonischemic etiologies and development of HFpEF. Also, AAs may respond differently to pharmacotherapy.18 Thus, our understanding and treatment of HF in AAs are limited, making it important to investigate symptoms in this high-risk population.
The evaluation of dyspnea in HF patients must include a comprehensive history and examination. The use of dyspnea instruments such as the Borg scale or VAS will allow for a rating of intensity and measurement of the patient’s perception of his/her breathing. These instruments are short and simple for the patient to use. However, the reliability and sensitivity of these instruments for capturing changes resulting from interventions or monitoring treatment over time remain to be determined. During the early stages of HF, some patients may experience dyspnea only on exertion and may learn to “work through” their dyspnea, whereas in later stages, patients experience unrelieved dyspnea. The influence of disease progression on patients’ perceptions of the intensity of dyspnea and subsequent self-reported scores over time may vary with the individual. Therefore, using the MRC or the 6MWT may be helpful in evaluating the impact and functional impairment imposed by dyspnea.
These findings related to the experience of dyspnea and dyspnea measures in the understudied and vulnerable population of AAs with HFrEF and HFpEF are important. We used multiple dyspnea instruments and assessed patients’ dyspnea intensity at baseline and after activity with the 6MWT. This approach allows clinicians and researchers to examine dyspnea in an ambulatory setting.
Limitations include a small sample size and the use of a convenience sample from a single HF center. Because enrollment was limited to AA patients older than 50 years, findings may not be applicable to younger AA with HF or to other ethnic groups. Also, we used unidimensional instruments that did not capture all domains of dyspnea, especially the psychological component.
Summary and Implications
Dyspnea is a prevalent symptom in AA patients with HFpEF and HFrEF. Understanding how to measure and interpret changes in dyspnea in ambulatory patients is important. Acute dyspnea episodes will occur, and it is important to understand if these episodes represent worsening HF or lack of response to new medications or other interventions. Also, some patients will simply limit activity to avoid dyspnea, thereby promoting deconditioning. Therefore, measuring dyspnea subjectively and only at rest may not be best for determining the effect of dyspnea on daily functioning. The Borg scale was an effective instrument for detecting clinically meaningful change in dyspnea during and immediately after activity. More research is needed to determine which instrument(s) may be the most reliable to measure dyspnea at baseline and over a period, such as weeks to months. It is important to monitor dyspnea at rest and with activity to develop treatment strategies that optimize a patient’s ability to maintain daily functions, especially in the high-risk AA population.
What’s New and Important
- African Americans with stable chronic HFpEF and HFrEF receiving guideline-directed therapy experience a high prevalence of dyspnea at baseline and after activity.
- The increase in the intensity of dyspnea in response to activity was similar between patients with HFpEF and patients with HFrEF.
- The validity and reliability of single-dimension dyspnea instruments vary with the patient’s condition (baseline or rest vs activity).
The authors thank Alana Steffen, PhD, for her statistical assistance and Kevin Grandfield for editorial assistance.
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Keywords:Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved
African Americans; dyspnea; heart failure; modified Borg scale