Reproducibility of Visual Analog Scale Measurements of Dyspnea in Patients with Chronic Obstructive Pulmonary Dlsease'?
M. JEFFERY MADOR and THOMAS J. KUFEL
Introduction
A need exists for a method of reliably quantifying the degree of dyspnea in patients during exercise that would allow comparison between studies. The visual analog scale (VAS), a vertical line with two anchor points, one at each extreme (1), has been used to quantify the degree of dyspnea during exercise (2-5). VAS measurements of dyspnea during exercise are reproducible within an individual subject when exercise is repeated on the same day or severaldays after the initial study (2,4). The short-term reproducibility of VAS dyspnea measurements has been confirmed in both normal subjects and patients with chronic obstructive pulmonary disease (COPD) (2, 4). Studies in normal subjects suggest that the reproducibility of VAS measurements of dyspnea may deteriorate with time (2, 3). The moderate or long-term reproducibility of VAS dyspnea measurements in patients with COPD is unknown. This information is important to determine whether VAS measurements of dyspnea are likely to be useful in assessing the response to therapeutic interventions. The present study, therefore, evaluated the reproducibility of VAS measurements over an 8-wk period in patients with COPD. VAS measurements were obtained during incremental exercise on a cycle ergometer to a symptom-limited maximum. There is no universally accepted definition of dyspnea, but everybody has experienced the sensation and thus has an intuitive understanding of the phenomenon. Because of the lack of an accepted definition, some investigators have asked subjects to rate their degree of dyspnea without defining the sensation (6, 7). With this approach, it is possible that different subjects will be quantifying different sensations. Furthermore, the experimental subject's notion of dyspnea may be different from that of the inves82
SUMMARY The purpose of this study was to evaluate the reproducibility of Visual analog scale ratings of the effort to breathe (VAS.) and the degree of discomfort evoked by breathing (VASd) In patients with chronic obstructlva pulmonary disease (COPO) during exercise. Six subjects with moderately severe COPO (FEV, 1.12 :I: 0.29 L, FEV,/FVC 44 :I: 4%) underwent progresslva Incremental exercise testing to a symptom-limited maximum every week for 8 Wk. VAS. and VASd were highly correlated In each subJect (r 0.99 :I: 0.01). The slope of the VASdIVAS. relationship for all trials In all subJectswes not significantly different from 1, Indicating that our subJects were rating a common sensation with the two scales. VAS. at maximal exercise was reproducible In ev· ery subJect; the within-subJect coefficient of variation (CV)was 6% (range, 2 to 10%) and compared favorably with physiologic Indices: 7% (range, 3 to 12%) for oxygen consumption and 10% (range, 5 to 16%) for minute vantllallon (VI). In contrast, submaxlmal VAS ratings were highly variable. At 66% of the maximal work load, the within-subject CV for VAS. was 21% (range, 11 to 28%) compared with 6% (range, 4 to 7%) for ve, (p < 0.003) and 10% (range, 5 to 16%) for VI (p < 0.01). VAS. correlated linearly with VI and vo, In all SUbjects In all trials. Howevar, within an IndiVidual subJect the slopa and position of these relationships varied widely between trials. We conclude that although maximal VAS retlngs are reproducible, submaxlmal VAS ratings and the relationship be· tween VAS ratings and physiologic Indices vary considerably when exercise tests are performed at weekly Intervals In patients with COPO. AM REV RESPIR DIS 1"2; 148:82-87
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tigator. Other investigators have provided definitions for dyspnea ranging from those related to the amount of "difficulty" or "effort" involved in breathing (8, 9)to those related to the ''uncomfortable'' nature of the sensation (2, 3). In this study, we asked subjects to rate both the "effort to breathe" and the degree of "respiratory discomfort" on separate visual analog scales. The reproducibility of both visual analog scales and their relationship to each other were examined. Furthermore, the relationship between the two visual analogue scales and standard indicesof exercise intensitywas examined. Methods Subjects Six male subjects with established COPD, 63 ± 5.7 yr of age, were studied. Their mean weight and height were 76 ± 8.3 kg and 173 ± 7.2 em, respectively. The study was approved by the appropriate institutional review boards, and informed consent was obtained from all subjects. However, all subjects were naive to the purposes of the experiment. All subjects were clinically stable outpatients receiving a regular schedule of orally ad-
ministered or inhaled bronchodilators. Four subjects were receiving prednisone (dose range, 8 to 10 mg).
Pulmonary Function Testing FVC, FEV.. and maximal voluntary ventilation were measured using a dry rolling-seal spirometer (Model 822; Ohio Instruments, Madison, WI). FRC and residual volume(RV) were measured by body plethysmography (P. K. Morgan, Chatham, Kent, UK). Arterial blood gas tensions wereobtained while patients breathed room air at rest using a pHI
(Received in original form July 19, 1991 and in revised form February 14, 1992) 1 From the Division of Pulmonary Medicine, State University of New York at Buffalo, and the Veterans Administration Medical Center, Buffalo, New York. 1 Supported by grants from the American Lung Association of New York and from the American Heart Association of New York and by VAMedical Research Funds. 3 Correspondence and requests for reprints should be addressed to M. Jeffery Mador, M.D., State University of New York at Buffalo (SUNY), Pulmonary Division, Department of Medicine, VA Medical Center, 3495 Bailey Avenue, Buffalo, NY 14215.
83
REPRODUCIBILITY OF DYSPNEA MEASUREMENTS IN COPO
blood gas analyzer (ABL-3; Radiometer, Copenhagen, Denmark). Predicted normal values werethose 0 f Crapo and coworkers (10, 11). Maximal inspiratory pressure (MIP) was measured with a differential pressure transducer (Model MP-45 ± 350 em H,O; Validyne Corp., Northridge, CA) while performing a maximal inspiratory effort against an occluded airway near RV(12). To prevent glottic closure, a small leak was produced by insertion of an 18-gauge needle in the mouthpiece. MIP maneuvers were repeated until three reproducible measurements that could be sustained for at least 1 s were recorded.
Apparatus The subjects breathed through a two-waynonrebreathing valve of low resistance and dead space (Model 2700; Hans Rudolph, Kansas City, MO). Inspiratory flow was measured with a pneumotachograph (Model 3813; Hans Rudolph) and a differential pressure transducer (Model MP-45; Validyne). Tidal volume (VT) was obtained by integration of the flow signal. Expired gas was passed through a mixing chamber and analyzed for 0, and CO, by a paramagnetic 0, analyzer and an infrared CO, analyzer, respectively. The heart rate (HR) was determined from the electrocardiograph. Average values of VI, VT, HR, 0, uptake (Vo,), and CO, production (Vco.) were calculated every 30 s. The inspiratory flow signal was recorded on a strip chart recorder (Gould Inc., Cleveland, OH), and inspiratory time (11), expiratory time (Th), and fractional inspiratory time (Tt/Ttot) weremeasured from this tracing. Oxygen saturation was measured with a pulse oximeter (Biox III; Ohmeda, Boulder, CO). Mouth occlusion pressure (Pe.i) was measured in a standard fashion (13) using a commercialinflatable balloon system (Model 9300; Hans Rudolph) attached to the inspiratory limb of the breathing circuit. A pneumatic hand switch, which controlled balloon inflation and deflation, was employed to occlude the inspiratory line of the circuit during expiration and to main- . tain this occlusion for the first 0.25 to 0.30 s of the subsequent inspiration. The pressure was measured at the mouth with a differential pressure transducer (Model MP-45; Validyne) and recorded on a strip chart recorder (Gould) run at a paper speed of 125 mm/s. The maximal pressure that developed 100ms after the start of inspiration (Pe.s) was calculated from the pressure tracing. Three to five occlusion pressures wereobtained during the first 30 s of each work load. Visual Analog Scale Patients were asked to rate both "the sense of effort" required to breathe and the degree of "discomfort" associated with breathing using separate visual analog scales (VAS). Both scalesconsisted of a verticalstraight line, 100mm in length. The first scale was labeled "breathing very very hard" at the top and "breathing very veryeasy" at the bottom. The second scale was labeled "breathing very very
uncomfortable" at the top and "no discomfort" at the bottom. For measurements of effort to breathe, patients were instructed to point to a spot on the line indicating the intensity of their sensation of respiratory effort at that particular point in time (an attendant made the actual mark on the line). The subjects were specifically instructed to scale their "effort to breathe" and to disregard any other sensations associated with whole-body exercise. For measurements of respiratory discomfort, the patients were instructed to rate the degree of discomfort evoked by breathing. The visual analog scales were presented in random order 10 s apart during the last 30 s of each work load.
Exercise Testing Patients performed progressive incremental exercisetests to a symptom-limited maximum on an electronically braked cycle ergometer (Rodby Elektronik; Enhorna, Sweden). Tests were performed with the patients breathing room air. Prior to each test, the patients rested while sitting on the bicycle for 5 min to acclimatize to the breathing circuit. After 1 min of unloaded cycling,the work load was increased by 15 W each minute until the patient was unable to continue. All tests were stopped by the patients because of dyspnea. Predicted normal values for maximal oxygen consumption (Vo,max) based on age, height, and sex were those of Jones and coworkers (14). Predicted maximal heart rate (HRmax) was based on the equation: HRmax (beats/ min) = 210 - 0.65 age (15). Exercise testing was performed weedy for 8 wk. Spirometry was performed on each study day to determine whether lung function had remained stable. Patients were instructed to maintain their regular diets, and all of them were continued on their regular regimens of oral and inhaled bronchodilators throughout the study period. Exercise testing was performed at approximately the same time of day to avoid diurnal variation in pulmonary function. A long-acting aerosol bronchodilator (Albuterol, two puffs) was administered via a spacer device (Inspir-Ease) 1 h prior to exercise testing. Data Analysis Variability of objective and subjective mea-
surements was assessed from mean absolute values and from the coefficient of variation (4, 8, 16). To assess variability during submaximal exercise, the work loads that most closelyapproximated 33 and 66070 of the subject's maximal work load (Wmax) were determined, and subjective and objective measurements werecompared at these work loads in all trials for that subject. Statistical significance of differences in mean values of objective and subjective measurements was determined by repeated measures analysis of variance (17). If the F value was significant, Thkey's multiple comparison test was employed to determine which study days were responsible (18). The relationship between VAS score and objective indices (Vo" Vr, or po.,) was calculated by linear regression using the least squares method. Differences across study days in the relationship between VAS score and objective indices was determined by analysis of covariance (19).The results are expressed as the mean ± standard deviation unless otherwise stated, and p
M. JEFFERY MADOR and THOMAS J. KUFEL
Introduction
A need exists for a method of reliably quantifying the degree of dyspnea in patients during exercise that would allow comparison between studies. The visual analog scale (VAS), a vertical line with two anchor points, one at each extreme (1), has been used to quantify the degree of dyspnea during exercise (2-5). VAS measurements of dyspnea during exercise are reproducible within an individual subject when exercise is repeated on the same day or severaldays after the initial study (2,4). The short-term reproducibility of VAS dyspnea measurements has been confirmed in both normal subjects and patients with chronic obstructive pulmonary disease (COPD) (2, 4). Studies in normal subjects suggest that the reproducibility of VAS measurements of dyspnea may deteriorate with time (2, 3). The moderate or long-term reproducibility of VAS dyspnea measurements in patients with COPD is unknown. This information is important to determine whether VAS measurements of dyspnea are likely to be useful in assessing the response to therapeutic interventions. The present study, therefore, evaluated the reproducibility of VAS measurements over an 8-wk period in patients with COPD. VAS measurements were obtained during incremental exercise on a cycle ergometer to a symptom-limited maximum. There is no universally accepted definition of dyspnea, but everybody has experienced the sensation and thus has an intuitive understanding of the phenomenon. Because of the lack of an accepted definition, some investigators have asked subjects to rate their degree of dyspnea without defining the sensation (6, 7). With this approach, it is possible that different subjects will be quantifying different sensations. Furthermore, the experimental subject's notion of dyspnea may be different from that of the inves82
SUMMARY The purpose of this study was to evaluate the reproducibility of Visual analog scale ratings of the effort to breathe (VAS.) and the degree of discomfort evoked by breathing (VASd) In patients with chronic obstructlva pulmonary disease (COPO) during exercise. Six subjects with moderately severe COPO (FEV, 1.12 :I: 0.29 L, FEV,/FVC 44 :I: 4%) underwent progresslva Incremental exercise testing to a symptom-limited maximum every week for 8 Wk. VAS. and VASd were highly correlated In each subJect (r 0.99 :I: 0.01). The slope of the VASdIVAS. relationship for all trials In all subJectswes not significantly different from 1, Indicating that our subJects were rating a common sensation with the two scales. VAS. at maximal exercise was reproducible In ev· ery subJect; the within-subJect coefficient of variation (CV)was 6% (range, 2 to 10%) and compared favorably with physiologic Indices: 7% (range, 3 to 12%) for oxygen consumption and 10% (range, 5 to 16%) for minute vantllallon (VI). In contrast, submaxlmal VAS ratings were highly variable. At 66% of the maximal work load, the within-subject CV for VAS. was 21% (range, 11 to 28%) compared with 6% (range, 4 to 7%) for ve, (p < 0.003) and 10% (range, 5 to 16%) for VI (p < 0.01). VAS. correlated linearly with VI and vo, In all SUbjects In all trials. Howevar, within an IndiVidual subJect the slopa and position of these relationships varied widely between trials. We conclude that although maximal VAS retlngs are reproducible, submaxlmal VAS ratings and the relationship be· tween VAS ratings and physiologic Indices vary considerably when exercise tests are performed at weekly Intervals In patients with COPO. AM REV RESPIR DIS 1"2; 148:82-87
=
=
=
tigator. Other investigators have provided definitions for dyspnea ranging from those related to the amount of "difficulty" or "effort" involved in breathing (8, 9)to those related to the ''uncomfortable'' nature of the sensation (2, 3). In this study, we asked subjects to rate both the "effort to breathe" and the degree of "respiratory discomfort" on separate visual analog scales. The reproducibility of both visual analog scales and their relationship to each other were examined. Furthermore, the relationship between the two visual analogue scales and standard indicesof exercise intensitywas examined. Methods Subjects Six male subjects with established COPD, 63 ± 5.7 yr of age, were studied. Their mean weight and height were 76 ± 8.3 kg and 173 ± 7.2 em, respectively. The study was approved by the appropriate institutional review boards, and informed consent was obtained from all subjects. However, all subjects were naive to the purposes of the experiment. All subjects were clinically stable outpatients receiving a regular schedule of orally ad-
ministered or inhaled bronchodilators. Four subjects were receiving prednisone (dose range, 8 to 10 mg).
Pulmonary Function Testing FVC, FEV.. and maximal voluntary ventilation were measured using a dry rolling-seal spirometer (Model 822; Ohio Instruments, Madison, WI). FRC and residual volume(RV) were measured by body plethysmography (P. K. Morgan, Chatham, Kent, UK). Arterial blood gas tensions wereobtained while patients breathed room air at rest using a pHI
(Received in original form July 19, 1991 and in revised form February 14, 1992) 1 From the Division of Pulmonary Medicine, State University of New York at Buffalo, and the Veterans Administration Medical Center, Buffalo, New York. 1 Supported by grants from the American Lung Association of New York and from the American Heart Association of New York and by VAMedical Research Funds. 3 Correspondence and requests for reprints should be addressed to M. Jeffery Mador, M.D., State University of New York at Buffalo (SUNY), Pulmonary Division, Department of Medicine, VA Medical Center, 3495 Bailey Avenue, Buffalo, NY 14215.
83
REPRODUCIBILITY OF DYSPNEA MEASUREMENTS IN COPO
blood gas analyzer (ABL-3; Radiometer, Copenhagen, Denmark). Predicted normal values werethose 0 f Crapo and coworkers (10, 11). Maximal inspiratory pressure (MIP) was measured with a differential pressure transducer (Model MP-45 ± 350 em H,O; Validyne Corp., Northridge, CA) while performing a maximal inspiratory effort against an occluded airway near RV(12). To prevent glottic closure, a small leak was produced by insertion of an 18-gauge needle in the mouthpiece. MIP maneuvers were repeated until three reproducible measurements that could be sustained for at least 1 s were recorded.
Apparatus The subjects breathed through a two-waynonrebreathing valve of low resistance and dead space (Model 2700; Hans Rudolph, Kansas City, MO). Inspiratory flow was measured with a pneumotachograph (Model 3813; Hans Rudolph) and a differential pressure transducer (Model MP-45; Validyne). Tidal volume (VT) was obtained by integration of the flow signal. Expired gas was passed through a mixing chamber and analyzed for 0, and CO, by a paramagnetic 0, analyzer and an infrared CO, analyzer, respectively. The heart rate (HR) was determined from the electrocardiograph. Average values of VI, VT, HR, 0, uptake (Vo,), and CO, production (Vco.) were calculated every 30 s. The inspiratory flow signal was recorded on a strip chart recorder (Gould Inc., Cleveland, OH), and inspiratory time (11), expiratory time (Th), and fractional inspiratory time (Tt/Ttot) weremeasured from this tracing. Oxygen saturation was measured with a pulse oximeter (Biox III; Ohmeda, Boulder, CO). Mouth occlusion pressure (Pe.i) was measured in a standard fashion (13) using a commercialinflatable balloon system (Model 9300; Hans Rudolph) attached to the inspiratory limb of the breathing circuit. A pneumatic hand switch, which controlled balloon inflation and deflation, was employed to occlude the inspiratory line of the circuit during expiration and to main- . tain this occlusion for the first 0.25 to 0.30 s of the subsequent inspiration. The pressure was measured at the mouth with a differential pressure transducer (Model MP-45; Validyne) and recorded on a strip chart recorder (Gould) run at a paper speed of 125 mm/s. The maximal pressure that developed 100ms after the start of inspiration (Pe.s) was calculated from the pressure tracing. Three to five occlusion pressures wereobtained during the first 30 s of each work load. Visual Analog Scale Patients were asked to rate both "the sense of effort" required to breathe and the degree of "discomfort" associated with breathing using separate visual analog scales (VAS). Both scalesconsisted of a verticalstraight line, 100mm in length. The first scale was labeled "breathing very very hard" at the top and "breathing very veryeasy" at the bottom. The second scale was labeled "breathing very very
uncomfortable" at the top and "no discomfort" at the bottom. For measurements of effort to breathe, patients were instructed to point to a spot on the line indicating the intensity of their sensation of respiratory effort at that particular point in time (an attendant made the actual mark on the line). The subjects were specifically instructed to scale their "effort to breathe" and to disregard any other sensations associated with whole-body exercise. For measurements of respiratory discomfort, the patients were instructed to rate the degree of discomfort evoked by breathing. The visual analog scales were presented in random order 10 s apart during the last 30 s of each work load.
Exercise Testing Patients performed progressive incremental exercisetests to a symptom-limited maximum on an electronically braked cycle ergometer (Rodby Elektronik; Enhorna, Sweden). Tests were performed with the patients breathing room air. Prior to each test, the patients rested while sitting on the bicycle for 5 min to acclimatize to the breathing circuit. After 1 min of unloaded cycling,the work load was increased by 15 W each minute until the patient was unable to continue. All tests were stopped by the patients because of dyspnea. Predicted normal values for maximal oxygen consumption (Vo,max) based on age, height, and sex were those of Jones and coworkers (14). Predicted maximal heart rate (HRmax) was based on the equation: HRmax (beats/ min) = 210 - 0.65 age (15). Exercise testing was performed weedy for 8 wk. Spirometry was performed on each study day to determine whether lung function had remained stable. Patients were instructed to maintain their regular diets, and all of them were continued on their regular regimens of oral and inhaled bronchodilators throughout the study period. Exercise testing was performed at approximately the same time of day to avoid diurnal variation in pulmonary function. A long-acting aerosol bronchodilator (Albuterol, two puffs) was administered via a spacer device (Inspir-Ease) 1 h prior to exercise testing. Data Analysis Variability of objective and subjective mea-
surements was assessed from mean absolute values and from the coefficient of variation (4, 8, 16). To assess variability during submaximal exercise, the work loads that most closelyapproximated 33 and 66070 of the subject's maximal work load (Wmax) were determined, and subjective and objective measurements werecompared at these work loads in all trials for that subject. Statistical significance of differences in mean values of objective and subjective measurements was determined by repeated measures analysis of variance (17). If the F value was significant, Thkey's multiple comparison test was employed to determine which study days were responsible (18). The relationship between VAS score and objective indices (Vo" Vr, or po.,) was calculated by linear regression using the least squares method. Differences across study days in the relationship between VAS score and objective indices was determined by analysis of covariance (19).The results are expressed as the mean ± standard deviation unless otherwise stated, and p
