1. health and fitness
2. exercise

Original Research
COPD
Perceptual and Physiologic Responses
During Treadmill and Cycle Exercise in
Patients With COPD*
James A. Murray, DO; Laurie A. Waterman, BS; Joseph Ward, RCPT;
John C. Baird, PhD; and Donald A. Mahler, MD
Background: Although the cycle ergometer is the traditional mode for exercise testing in patients
with respiratory disease, this preference over the treadmill does not consider perceptual responses.
Our hypotheses were as follows: (1) the regression slope between breathlessness and oxygen
consumption (V˙O2) is greater on the treadmill than on the cycle ergometer; and (2) the regression
slope between leg discomfort and V˙O2 is greater on the cycle ergometer than on the treadmill.
Methods: Twenty patients (10 men/10 women) with COPD (mean ⴞ SD postbronchodilator FEV1,
50 ⴞ 15% of predicted) used a continuous method to report changes in breathlessness and in leg
discomfort during cycle and treadmill exercise.
Results: Patients reported an earlier onset of breathlessness and leg discomfort during cycling. Peak
ratings of breathlessness were higher on the treadmill, whereas peak ratings of leg discomfort were
higher on the cycle ergometer. The regression slopes for breathlessness as a function of V˙O2 and of
minute ventilation (VE) were higher on the treadmill. The regression slopes between leg discomfort
and V˙O2 were similar for treadmill and cycle exercise. Peak V˙O2 was significantly higher with treadmill
exercise (mean ⌬ ⴝ 8%; p ⴝ 0.002).
Conclusions: Patients with COPD exhibit different perceptual and physiologic responses during
treadmill walking and cycling. Although ratings of breathlessness are initially higher with cycling at
equivalent levels of V˙O2, the changes in breathlessness as a function of physiologic stimuli (V˙O2 and VE)
are greater during treadmill exercise. Leg discomfort is the predominant symptom throughout
cycling.
(CHEST 2009; 135:384 –390)
Key words: continuous ratings of breathlessness; continuous ratings of leg discomfort; COPD; cycle ergometry; treadmill
exercise
Abbreviations: V˙co2 ⫽ carbon dioxide production; Ve ⫽ minute ventilation; V˙o2 ⫽ oxygen consumption
ergometry and walking tests are employed
C toycleevaluate
an individual’s responses as part of
cardiopulmonary exercise testing. With cycle ergometry, the work performed can be quantified, and the
*From Pulmonary Medicine and Critical Care (Dr. Murray),
Unity Health System, Rochester, NY; Pulmonary Function and
Cardiopulmonary Exercise Laboratories (Ms. Waterman and Mr.
Ward), Dartmouth-Hitchcock Medical Center, Lebanon, NH;
Section of Pulmonary and Critical Care Medicine (Dr. Mahler),
Dartmouth Medical School, Lebanon, NH; and Psychological
Applications, LLC (Dr. Baird), South Pomfret, VT.
Dr. Baird is Scientific Director of Psychological Applications,
LLC, which owns the copyright of the continuous measurement
program. The other authors have no conflicts of interest to
disclose.
Manuscript received May 23, 2008; revision accepted August 1,
2008.
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relationship between oxygen consumption (V˙o2) and
work rate can be used to identify abnormalities.1,2
Other advantages of the cycle ergometer are safety
and less weight bearing compared with the treadmill.2 For these reasons, the cycle ergometer has
been recommended for exercise testing of patients
with respiratory disease.1–3 However, the expressed
Reproduction of this article is prohibited without written permission
from the American College of Chest Physicians (www.chestjournal.
org/misc/reprints.shtml).
Correspondence to: Donald A. Mahler, MD, FCCP, Section of
Pulmonary and Critical Care Medicine, Dartmouth-Hitchcock
Medical Center, One Medical Center Dr, Lebanon, NH 037560001; e-mail: [email protected]
DOI: 10.1378/chest.08-1258
Original Research
preference for the cycle ergometer over the treadmill does not consider perceptual responses during
exercise.
Exercise tests are “symptom-limited” because individuals stop due to intolerable or unpleasant experiences.2,4 In general, patients with COPD report
that breathlessness limits walking but describe more
intense leg effort/fatigue with cycling.5–7 In these
comparative studies,5–7 patients rated symptom intensity only at the end of the exercise test. Although
such ratings indicate which symptom causes a person
to stop exercise, peak values do not discriminate
between healthy individuals and patients with cardiorespiratory disease and are not responsive to
therapy.8 –10 The recommended procedure is for the
individual to rate the intensity of symptoms throughout exercise.2 Both discrete (patient is queried at
specific periods) and continuous (patient provides a
rating whenever he/she experiences a change) methods are available.9 With either method, the functional relationship between perceptual and physiologic continua can be assessed.
The major purpose of the present study was to
compare perceptual and physiologic responses obtained during cycle ergometry and treadmill exercise. Patients used the continuous method to report
whenever there was a change in breathlessness or a
change in leg discomfort throughout exercise. Our
hypotheses were as follows: (1) the regression slope
between breathlessness and V˙o2 is greater on the
treadmill than on the cycle ergometer; and (2) the
regression slope between leg discomfort and V˙o2 is
greater on the cycle ergometer than on the treadmill.
Preliminary results of this investigation have been
presented in abstract form.11
Materials and Methods
sorMedics; Yorba Linda, CA) 关randomized order兴, and practiced
using the continuous method for rating breathlessness and leg
discomfort. For treadmill exercise, a modified Balke protocol was
used. The highest speed that the subject could maintain for 10
min at visit 1 was used for subsequent testing, and the incline was
increased by 0.5% each minute. For cycle ergometry, a ramp
protocol (8 to 12 W/min) was used.
The subject was instructed not to take any inhaled bronchodilator medications for 12 h prior to visits 2 and 3. At these visits,
the subject performed spirometry before and 20 min after
inhaling two puffs of albuterol (180 ␮g) via metered-dose inhaler,
and then completed an incremental exercise test randomized by
mode of exercise (cycle ergometer or treadmill).
Expired gas was analyzed for minute ventilation (Ve), V˙o2, and
carbon dioxide production (V˙co2) for every breath using a
metabolic measurement system (MedGraphics Cardiorespiratory
Diagnostic Systems; MedGraphics; St. Paul, MN). The system
was calibrated before each test. Oxygen saturation was recorded
using pulse oximeter (Nellcor; Hayward, CA). At each visit, the
patient read written instructions and provided separate ratings of
breathlessness and leg discomfort throughout exercise16:
This is a scale for rating breathlessness and leg discomfort.
The number 0 represents no breathlessness and no leg
discomfort. The number 10 represents the strongest or
greatest breathlessness or leg discomfort that you have
ever experienced. You should adjust the length of the blue
bar to represent your perceived level of breathlessness by
pressing the left button on the mouse. You should adjust
the length of the red bar to represent your perceived level
of leg discomfort by pressing the right button on the
mouse. Use the written descriptions to the right of the
numbers to help guide your selection. You should increase
the length of each bar whenever you experience a change
in breathlessness or leg discomfort.
An illustration of the computer display is shown in Figure 1.
The methodology has been described previously.17 At the end of
each test, the subject was asked, “Why did you stop exercise:
breathlessness, leg discomfort, or both?”
Statistical Analysis
The primary outcomes were the relationships between ratings
of breathlessness and of leg discomfort as a function of V˙o2.17–20
Subjects
Inclusion criteria were as follows: age ⱖ 50 years; diagnosis of
COPD12; ⱖ 10 pack-year history of cigarette smoking; ability to
exercise on the cycle ergometer and treadmill; and clinically
stable COPD. Institutional review board approved the study, and
written informed consent was obtained from each participant.
Experimental Protocol
Each patient was tested at three visits, separated from each
other by 2 to 4 days. At visit 1, the following assessments were
made: medical history, vital signs, current medications, physical
examination, resting ECG, and self-administered computerized
version of the baseline dyspnea indexes.13 Spirometry and diffusing capacity (Collins model CPL; Collins; Louisville, CO) were
performed. Predicted values were taken from Crapo et al14 and
from Gaensler and Smith,15 respectively. The patient then walked
on the treadmill (Full Vision; Newton, KS), pedaled on an
electronically braked cycle ergometer (Ergo-Metrics 800S; Senwww.chestjournal.org
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Figure 1. Display of dual ratings of breathlessness and leg
discomfort during exercise. The subject provides ratings throughout exercise by clicking the left (for a change in breathlessness) or
right (for a change in leg discomfort) buttons of the computer
mouse. Only the final ratings are shown in the illustration.
CHEST / 135 / 2 / FEBRUARY, 2009
385
Table 1—Descriptive Characteristics of Patients*
Characteristics
Data
Female/male gender, No.
Age, yr
Height, cm
Weight, kg
FVC, L
% predicted
FEV1
Baseline, L
% predicted
Post-BD, L
% predicted
Post-BD FEV1/FVC, %
Diffusing capacity, mL/min/mm Hg
% predicted
Baseline dyspnea index†
10/10
62 ⫾ 7
167.6 ⫾ 7.9
75.4 ⫾ 14.0
3.05 ⫾ 0.74
83 ⫾ 13
1.18 ⫾ 0.35
45 ⫾ 13
1.32 ⫾ 0.42
50 ⫾ 15
41 ⫾ 13
13.8 ⫾ 3.7
58 ⫾ 18
5.9 ⫾ 1.4
*Data are presented as mean ⫾ SD unless otherwise indicated.
Post-BD ⫽ postbronchodilator.
†Self-administered and computerized version.13
Both linear regression and power function models were fit to the
data.21,22 For each subject, Pearson correlation coefficients were
calculated to determine the best-fitting linear and power relationships. Secondary outcomes were the onset of breathlessness
and of leg discomfort as previously defined.17,20 In addition,
ratings of breathlessness and of leg discomfort were compared
between treadmill walking and cycling at a standardized V˙o2.
Comparisons of study conditions were performed using paired
t tests. Data are reported as mean ⫾ SD. The Cochran Q test was
used to test for differences in the reported symptoms that limited
exercise under different conditions; p ⱕ 0.05 (two-tailed test) was
considered statistically significant.
Results
Descriptive characteristics of the 20 patients are
given in Table 1. There were no significant differences
for postbronchodilator values for lung function at the
two visits. Respiratory medications included the following: albuterol metered-dose inhaler (n ⫽ 20); inhaled
long-acting ␤-agonist (n ⫽ 13); inhaled short- or
long-acting anticholinergic medications (n ⫽ 15); inhaled corticosteroids (n ⫽ 10); and oral theophylline
(n ⫽ 4).
Physiologic and perceptual results from incremental cardiopulmonary exercise tests are presented in
Tables 2 and 3, respectively. Because there were no
differences in the magnitude of the correlations
between linear and power function models (all values were ⱖ 0.91 for individual patients), the results
from the linear model are presented.
Physiologic Responses
With treadmill exercise, patients exercised longer,
had a higher peak V˙o2 (mean ⌬ ⫽ 8%; Fig 2), but
exhibited similar values for peak heart rate and peak
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Table 2—Postbronchodilator FEV1 and Physiologic
Results of Cardiopulmonary Exercise Testing*
Variables
Treadmill
Cycle
Ergometer
Post-BD FEV1, L
% predicted
Peak values
Heart rate,
beats/min
V˙o2, mL/kg/min
Ve, L/min
Respiratory rate,
breaths/min
V˙co2, L/min
Sao2, %
Change from rest
1.34 ⫾ 0.48
50 ⫾ 15
1.32 ⫾ 0.37
50 ⫾ 14
130 ⫾ 17
129 ⫾ 19
16.3 ⫾ 5.1
38.7 ⫾ 12.2
31.8 ⫾ 7.8
15.1 ⫾ 4.4†
42.1 ⫾ 13.9†
36.1 ⫾ 7.9†
1.10 ⫾ 0.41
90.4 ⫾ 4.8
⫺ 5.4 ⫾ 4.6
1.16 ⫾ 0.33
93.8 ⫾ 2.8†
⫺ 2.7 ⫾ 2.7†
*Sao2 ⫽ arterial oxygen saturation.
†p ⬍ 0.05 comparing results on treadmill vs cycle ergometer.
V˙co2 compared with cycle ergometry. Peak values
for Ve and respiratory rate were higher with cycling
than with walking. Resting values for oxygen saturation were similar, but patients had significantly
greater desaturation with treadmill exercise (mean
⌬ ⫽ ⫺ 5.4%) compared with cycle ergometry (mean
⌬ ⫽ ⫺ 2.7%) 关p ⬍ 0.001兴.
Perceptual Responses
Individual and mean values for the slopes of the
regressions between breathlessness and V˙o2 (Fig 3)
Table 3—Perceptual Responses of Cardiopulmonary
Exercise Testing*
Variables
Symptom ratings
Breathlessness
No. of ratings
Peak value
Leg discomfort
No. of ratings
Peak value
Reason for stopping
Breathlessness
Leg discomfort
Both the same
Onset of symptoms
V˙o2, mL/kg/min
Breathlessness
Leg discomfort
Calculated slopes
V˙o2, breathlessness
V˙e, breathlessness
V˙o2, leg discomfort
Treadmill
Cycle Ergometer
17.4 ⫾ 6.1
8.5 ⫾ 2.2
11.1 ⫾ 4.5†
6.7 ⫾ 3.1†
11.4 ⫾ 6.2
5.5 ⫾ 3.2
11.7 ⫾ 3.7
6.8 ⫾ 2.6†
19
0
1
8
10
2
11.9 ⫾ 4.0
12.4 ⫾ 4.2
9.4 ⫾ 3.6†
9.0 ⫾ 3.1†
1.90 ⫾ 0.91
0.76 ⫾ 0.46
1.37 ⫾ 0.90
1.17 ⫾ 0.68†
0.43 ⫾ 0.33†
1.11 ⫾ 0.63
*Data are presented as mean ⫾ SD. Onset of symptoms ⫽ V˙o2 value
corresponding to a rating of “just noticeable” or ⱖ 0.5 on the 0 –10
scale. The slope refers to linear regression between selected variables.
†Treadmill vs cycle ergometer, p ⬍ 0.05.
Original Research
Figure 2. Individual values for peak V˙o2 with cycle ergometry
and treadmill walking. Paired t tests show that mean values are
significantly higher with treadmill walking (p ⫽ 0.002).
and between breathlessness and Ve were significantly higher on the treadmill than on the cycle
ergometer (p ⬍ 0.001 for each comparison). Individual and mean values for the slopes of the
regression between leg discomfort and V˙o2 were
similar between treadmill and cycle exercise (Fig 4)
关p ⫽ 0.11兴.
The onset of breathlessness (Fig 3) and leg
discomfort (Fig 4) occurred at a lower V˙o2 with
cycling compared with treadmill walking (p ⬍ 0.05
for each comparison). Peak ratings of breathlessness were significantly higher on the treadmill
(⌬ ⫽ 1.8 ⫾ 1.6 U; p ⬍ 0.001). Peak ratings of leg
discomfort were significantly higher on the cycle
ergometer (⌬ ⫽ 1.3 ⫾ 1.1 U; p ⫽ 0.03). The main
reason for stopping exercise was breathlessness on
the treadmill and leg discomfort on the cycle
ergometer (p ⬍ 0.05).
At the onset of breathlessness on the treadmill, a
V˙o2 of 12 mL/kg/min was associated with perceptual
ratings of 0.4 ⫾ 1.3; at the same V˙o2 level, breathlessness ratings on the cycle were 3.0 ⫾ 2.6
(p ⬍ 0.001). For this same V˙o2, ratings of leg discomfort on the treadmill were 0.6 ⫾ 0.4 compared
with 3.6 ⫾ 2.1 on the cycle ergometer (p ⬍ 0.001).
Discussion
Our study demonstrates that patients with COPD
exhibit different perceptual and physiologic responses during treadmill walking and cycling. The
unique findings are as follows: (1) regression slopes
between breathlessness as a function of V˙o2 and of
Ve are significantly higher on the treadmill than on
the cycle ergometer; (2) the onset of breathlessness
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Figure 3. Top, A: Individual values for the regression slope
between breathlessness and V˙o2 during cycle and treadmill
exercise. The dashed line is the line of identity. Bottom, B: Mean
values for the relationship between breathlessness and V˙o2
during cycle and treadmill exercise. The onset of breathlessness
occurs at a lower V˙o2 during cycling than with treadmill exercise
(p ⬍ 0.001). Peak ratings for breathlessness are higher on the
treadmill than on the cycle ergometer (p ⬍ 0.001).
and leg discomfort occurs at a lower V˙o2 with cycling
compared with treadmill walking; and (3) leg discomfort is the predominant symptom throughout
cycle exercise compared with treadmill walking.
In 2000, Palange and colleagues6 reported that
nine patients with COPD had higher ratings of
breathlessness at the end of a shuttle walk test and
higher ratings of leg effort at the end of cycle
ergometry. Man and colleagues5 confirmed these
results in 84 patients with COPD, although Pepin
et al7 found no difference in peak ratings of dyspnea
between incremental cycling exercise and incremental shuttle walking. Although peak ratings can identify the reason that an individual stops exercise, the
peak intensity of a symptom is neither discriminative
nor responsive.8 –10 A more comprehensive approach
is recommended to examine the continuum of perceptual responses over a range of stimuli.2,10,23
CHEST / 135 / 2 / FEBRUARY, 2009
387
Figure 4. Top, A: Individual values for the regression slope
between leg discomfort and V˙o2 with the continuous method
during cycle and treadmill exercise. The dashed line is the line of
identity. Bottom, B: Mean values for the relationship between leg
discomfort and V˙o2 during cycle and treadmill exercise. The
onset of leg discomfort occurs at a lower V˙o2 during cycling than
with treadmill exercise (p ⬍ 0.001). Peak ratings for leg discomfort are higher on the cycle ergometer than on the treadmill
(p ⫽ 0.048).
After familiarization and practice at the initial
visit, our patients successfully used the continuous
method to report changes in breathlessness and in
leg discomfort throughout exercise. Although the
testing protocols that we used (modified Balke and
ramp of 8 to 12 W/min) are standard exercise tests,1,2
it is possible that different increments of work could
have altered the results. Regression analyses showed
higher slopes for breathlessness as a function of V˙o2
and of Ve with treadmill walking compared with
cycling (Table 3, Fig 3). These findings indicate that
once breathlessness is “just noticeable” by the patient, it increases faster with walking than with
cycling for comparable changes in metabolic load
and in the level of ventilation.
The regression slope between breathlessness and
V˙o2 has been used by various investigators18 –20,24 –26
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to discriminate between different populations and to
examine treatment effects. The regression slope for
an individual, however, depends to a great extent on
the initial (ie, the onset of symptoms) and final (ie,
peak ratings) data points. The continuous rating
method used in the present study enables the calculation of the onset of symptoms using different
procedures than typically employed in sensory psychophysics.21,22 A major finding in our study is that
patients had an onset of breathlessness at a lower
V˙o2 with cycling compared with treadmill walking
(Fig 3). Although we did not investigate possible
mechanisms for this finding, differences in metabolic
requirements and efficiency of the exercising muscles are evident with different modes of activity. For
example, during cycling the work is primarily performed by the quadriceps muscles. Man and colleagues5 showed that low frequency fatigue develops
in the quadriceps muscle after cycling, but not after
walking. Cycling uses less muscle mass, but produces
higher levels of blood lactate compared with walking.6,27 Higher blood lactate could contribute to the
earlier onset of breathlessness as observed in our
patients.
One or more mechanisms may explain the higher
regression slopes for breathlessness as a function of
V˙o2 and of Ve with treadmill walking compared with
cycling. Our patients exhibited greater oxygen desaturation with treadmill walking than with cycle
exercise, as has been previously reported by investigators.5–7 Palange and colleagues6 attributed this
difference to ventilation/perfusion mismatching during walking based on differences in body posture,
operating lung volumes, and/or pulmonary hemodynamics. With walking, the arm muscles are active
and could be a source of neurogenic impulses to the
respiratory center.6 In contrast, with cycling, the
hands are in a fixed position resting on the handle
bars, and the arms would be a less likely source of
neurogenic reflexes. This stabilized position supports
the shoulders and enables accessory muscles to
contribute to breathing. Any differences in coupling
between the muscles of locomotion and respiration
(ie, entrainment) and the magnitude of dynamic
hyperinflation between cycling and walking remain
to be determined.
The regression slopes between perceptual and
physiologic variables in this study represent a
continuum of changes throughout exercise. Examination of Figure 3, Bottom, B, shows that breathlessness is higher with cycle exercise compared
with treadmill exercise at low-to-moderate intensities of exertion. For example, at a standardized
V˙o2 of 12 mL/kg/min, patients reported higher
ratings of breathlessness with cycle exercise than
with treadmill walking. These observations highOriginal Research
light the fact that different aspects of the same
data may be relevant, depending on the objective
of the investigation.
Our results did not support the hypothesis that the
regression slope between leg discomfort and V˙o2 is
greater on the cycle ergometer than with treadmill
walking. However, Figure 4, Bottom, B demonstrates
clearly that leg discomfort is the predominant symptom throughout cycling. The earlier onset of leg
discomfort with cycling compared with treadmill
walking may be related to higher levels of lactate
being produced during cycling.6,27
The cycle ergometer has been used as the traditional mode for exercise testing in patients with lung
disease.2,4,28 Cycling is considered safer for the patient than a walking test because body weight is
supported and enables the workload to be quantified. Several investigations25,26,28 –31 have demonstrated improvements in cycling endurance time
and/or breathlessness ratings after bronchodilator
therapy. Although walking is a familiar activity for
most patients with COPD, cycling is an uncommon
physical effort. Man and colleagues5 showed that
cycling caused low-frequency fatigue of the quadriceps muscle and higher ratings of “leg effort” by
patients compared with breathlessness. With treadmill walking, our patients with COPD achieved a
significantly higher peak V˙o2 compared with cycling
(⌬ ⫽ 8%), and reported that breathlessness was the
major symptom limiting exercise. Pepin and colleagues7 reported an increase in walking endurance
time with the shuttle test after a single dose of
nebulized ipratropium bromide (500 ␮g), whereas
there was no significant change in cycling endurance
time. Morgan and Singh32 have proposed that walking may be a more appropriate exercise task to
demonstrate symptomatic benefit with bronchodilator therapy rather than cycling.
In conclusion, the present study extends our previous work by demonstrating that patients with
COPD are able to use the continuous method to
report breathlessness and leg discomfort concurrently throughout exercise tests. The results enhance
our knowledge by showing that patients with COPD
exhibit different perceptual and physiologic responses during treadmill walking and cycling. Measurement of the onset of symptoms, calculation of
regression slopes, along with recording peak ratings
provide comprehensive information about the relationship between perceptual responses and physiologic stimuli throughout exercise. We encourage
additional investigations to compare the efficacy of
therapies on perceptual and physiologic responses
associated with walking and cycling.
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Original Research