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* From the Centre for Exercise Science and Medicine, Institute of Biomedical and Life Sciences (Dr. Grant, Ms. Henderson, and Mr. Christie), and the Department of Statistics (Dr. Zare and Mr. Aitchison), University of Glasgow; and the Department of Cardiology (Drs. McMurray and Dargie), Western Infirmary, Glasgow, UK.
Correspondence to: S. Grant, PhD, Institute of Biomedical and Life Sciences, University of Glasgow, 64 Oakfield Ave, Glasgow, G12 8LT, UK; e-mail: S.Grant{at}bio.gla.ac.uk
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Abstract |
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 TOP Abstract IntroductionMaterials and MethodsResultsDiscussionThe Relationship Between the...ConclusionReferences |
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Design: Prospective clinical study.
Setting: Exercise laboratory.
Participants: Twenty-three physically active male subjects (mean ± SD age of 30 ± 4 years old) were recruited.
Intervention: Each subject attended
the exercise laboratory on four occasions at intervals of 1 week. Three
subjective scales were used: (1) the VAS (continuous scale); (2) the
Borg scale (12 fixed points); and (3) the Likert scale (LS; 5 fixed
points). Four identical submaximal tests were given (2 min at 60%
maximum oxygen uptake [
O2max] and 6
min at 70% O2max). Two tests
were undertaken to assess the reproducibility of scores that were
obtained with each subjective scale. Two other tests were undertaken to
assess the sensitivity of each scale to a change in symptom perception:
a double-blind treatment with propranolol, 80 mg, (ie,
active therapy; to increase the sensation of breathlessness and general
fatigue during exercise) or matching placebo. The subjective
scale scores were measured at 1 min 30 s, 5 min 30 s, and 7
min 15 s of exercise. Reproducibility was defined as the
proportion of total variance (ie, between-subject plus
within-subject variance) explained by the between-subject variance
given as a percentage. Sensitivity was defined as the effect of the
active drug therapy over the variation within subjects.
Results: Overall, the VAS performed best in terms of reproducibility for breathlessness and general fatigue, with reproducibility coefficients as high as 78%. For sensitivity, the VAS was best for breathlessness (ratio, 2.7) and the Borg scale was most sensitive for general fatigue (ratio, 3.0). The relationships between the respective psychological and physiologic variables were reasonably stable throughout the testing procedure, with overall typical correlations of 0.73 to 0.82
Conclusion: This study suggests that subjective scales can reproducibly measure symptoms during steady-state exercise and can detect the effect of a drug intervention. The VAS and Borg scales appear to be the best subjective scales for this purpose.
Key Words: breathlessness • exercise testing • general fatigue • reproducibility • sensitivity • subjective scales
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionThe Relationship Between the...ConclusionReferences |
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A comparison of the responses to these three scales would help determine which scale, if any, is more reproducible or more sensitive to change than the others. No study has compared the VAS, the Borg scale, and the LS. There is also limited information on subjective scales during steady-state exercise. In addition, little research has been done to determine the ability of the above scales to detect changes in status. The monitoring of subjective scales and physiologic variables provides information on the relationship between the variables. It may be expected that any differences in the physiologic stimuli would result in changes in the perception of breathlessness and general fatigue. A linkage of the perception of symptoms to physiologic variables may shed light on how symptoms are provoked. In addition, the establishment of an association between physiologic variables and subjective scales may provide an understanding of the mechanisms by which pharmacologic intervention can alleviate symptoms. If a cause and effect for symptoms could be identified, it may be possible to target a particular area in the treatment of patients.
The aims of this study are as follows: (1) to assess which subject scale, the VAS, the Borg scale, or the LS, if any, is decidedly more reproducible and sensitive to change in the assessment of symptoms; (2) to determine the magnitude of the visit and therapy effects of the subjective scales and physiologic variables; and (3) to compare the subjective scales with the physiologic responses to exercise.
Normal subjects were chosen for this study because it was considered that they would tolerate the test protocol better than patients and would provide information that could be applied to a patient population. In some instances, it is also difficult or undesirable to change transiently the status of some patient groups. It was hoped that submaximal exercise testing with a reproducible rating scale that was sensitive to change would provide an improved method of assessing therapeutic interventions in patients with CHF. In order to test the sensitivity of the scales, it is necessary to disrupt the normal status of the subjects so that the capability of the scales to detect change can be assessed. It was decided to use ß-blockade to elicit a change in the perception of breathlessness and general fatigue.
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Materials and Methods |
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The study received approval from the local ethical committee. All of the subjects completed a medical history questionnaire, underwent a medical examination, and signed a consent form before entry to the study.
Research Design
Preliminary Tests:
The subjects reported to the laboratory
at the same time of day. A submaximal economy test (running economy,
defined as the steady state oxygen uptake for a particular
running velocity1
) and a maximum test were carried out so
that relative intensities could be determined. A submaximal economy
profile was established for each subject using at least three 4-min
periods of treadmill exercise. After a 30-min rest, each subject then
undertook a symptom-limited maximal treadmill test to measure maximum
oxygen uptake (O2max). Depending on
submaximal performance, either a "Lamb Normal Subject Treadmill
Protocol" or a "Lamb Athlete Treadmill Protocol"2
was used for this test so that treadmill time was around 10 min. This
time period has been shown to be optimal for eliciting
O2max values.3
A number of criteria4
were used to define the quality of a
maximum test. A plateau in oxygen uptake
(O2) was defined as an
increase of not > 2.1 mL/kg/min or an increase of not > 5% in
energy cost with an increase in workload; 15 of 23 subjects
demonstrated a plateau in O2
based on the these criteria. All of the subjects attained their
age-predicted maximum heart rate (ie, 220 beats/min minus
age). All of the subjects had a respiratory exchange ratio
> 1.05, and 17 subjects had a respiratory exchange ratio
> 1.10.
Submaximal Tests:
The results of the symptom-limited maximal
test and the submaximal economy profile were used to devise a
standardized submaximal exercise protocol for each individual. This
consisted of an initial work rate of 60%
O2max that increased after 2 min to
70% O2max, a rate that was maintained
for an additional 6 min. Previous pilot work and publications by
this group5
have shown that this relative intensity is
appropriate to evaluate symptom scales. Exercise testing at only
moderate intensities (described by the authors6
as
exercise with a heart rate < 150 beats/min) has shown that
propranolol had no effect on the rating of perceived exertion. Two
minutes at 60% O2max provides a
warm-up, and the remaining 6 min at around 70%
O2max is of sufficient intensity to
elicit symptoms. Intensities much > 70%
O2max may produce marked discomfort
to subjects undergoing ß-blockade.
Experimental Protocol
Visits and Treatments:
Each subject attended the exercise
laboratory on four occasions at intervals of 1 week. The order of
visits was randomized according to a Latin rectangle design. The visits
were termed "Reproducibility One" (R1), "Reproducibility Two"
(R2), "Placebo", and "Active" (propranolol treatment). On
visits R1 and R2, no medication was administered. On the other two
occasions, propranolol, 80 mg, or a matching placebo was taken 12
h and 2 h before the exercise test. To test sensitivity, the
subjects were randomized to receive either propranolol or a matching
placebo prior to the two tests. Propranolol, 80 mg, was administered
because it is known to increase the perception of breathlessness and
general fatigue. Pilot work using the exercise protocol outlined above
showed that this dose given 12 h and 2 h before the test produced
an increase in the symptoms of breathlessness and general
fatigue.
Equipment (Treadmill, ECG, and Gas Analysis): Exercise testing was performed using a treadmill and ECG console (MAC2 Exercise Testing System; Marquette; Jupiter, FL). Heart rate was monitored using a three-lead ECG throughout all tests and was recorded during the last 10 s of each minute in all tests. Expired air was collected using a breathing valve (model 2700; Hans Rudolph; Kansas City, MO) with a mouthpiece that was attached by tubing to a metabolic cart (Classic Exercise System Model 2; Beckman Instruments; Anaheim, CA) that analyzed the expired gases. All subjects wore a noseclip. Before each test, the oxygen and carbon dioxide sensors were calibrated with standard gas mixtures. Volume was calibrated using the procedures outlined by the instruction manual (Beckman Instruments). Gas collection and analysis were continuous, and respiratory values for every 30 s were given on a printout.
Symptom Scales: During each test, symptom scales (see below) were administered at 1 min 30 s, 5 min 30 s, and 7 min 15 s. Two different scales were used at each time point. Each scale was used twice at each time point: once to measure breathlessness and once to measure general fatigue. In other words, a total of 12 symptom scores were recorded during each exercise test. The presentation of scales was alternated: VAS/other and other/VAS. Twelve subjects were randomized to the LS/VAS group, and 11 subjects were randomized to the Borg scale/VAS group. The symptom of breathlessness was always measured before general fatigue. With twice as many observations for the VAS, there will be a more precise estimate of reproducibility and sensitivity of VAS, but this in no way will that influence the magnitude of either reproducibility or sensitivity.
Each scale was administered using a computer (BBC Master; Acorn Computers; Cambridge, UK) and displayed on a color television screen placed at eye level in front of the subject while he exercised on the treadmill. The subject recorded his response using finger controls (see below), and the information was stored in the computer. An audible prompt was given each time a new scale appeared on the screen. On each occasion, the subjects had to move the lever before the cursor appeared on the screen (ie, before any score was displayed); therefore, the previous score was not displayed when the new scale was presented. A sliding lever allowed the subject to move the light cursor horizontally in either direction along the scale. Once the subject had chosen the desired score, he pressed a button to record it in the computer. At this point, another scale was displayed.
Subjective Scales: The VAS scale consisted of a horizontal line. The word "none" was placed at the left end of the scale, and "very severe" was placed at the right end of the scale. The VAS was scored from 0 to 100, but the subjects were unaware of the numbers. The Borg scale consisted of a vertical line labeled 0 to 10, with verbal descriptors at fixed points on the scale. The LS consisted of five boxes placed vertically, with the following verbal descriptors adjacent to each: not at all breathless, slightly breathless, moderately breathless, really quite breathless, and very breathless indeed. No study has used a LS to investigate breathlessness and general fatigue. Two symptoms were measured with the scales. The subjects were given the following instructions before each of the submaximal tests:
Breathlessness was described as follows: breathless, out of breath, air hunger, and unable to breathe enough. The subjects were asked to rate their sensation of breathlessness by referring to their common experience of an uncomfortable awareness of breathing and the descriptors outlined above. They were asked to avoid simply observing an increase in breathing and to disregard other sensations such as leg fatigue or general fatigue.
General fatigue was described as overall tiredness and overall fatigue. The subjects were asked to quantify general fatigue by referring to their common experience of general fatigue and the descriptors of general fatigue. They were instructed to disregard other sensations such as leg fatigue and breathlessness.
Statistical Methods
For each symptom scale and physiologic variable at each time
point, a generalized linear model was used to investigate possible
order of tests (ie, systematic learning effects),
differences among the tests, and treatment differences. The model also
included components of variability due to between-subject and
within-subject variation.
Reproducibility was defined as the proportion of the total variance (ie, between-subject plus within-subject variance) explained by the between-subject variance. Appropriate estimates of these were obtained using a generalized linear model incorporating visit, intervention, time point, and subject effects. In effect, this means that the subject differences are pooled to produce an estimate of the between-subject variance, while the residual sum of squares is the basis for the estimate of the within-subject variance. For example, if the between-subject variance was 278 and the within-subject variance was 63, the reproducibility coefficient would be 82% (ie, 278/[278 + 63]), a very good percentage. A score of 100% would signify perfect reproducibility (ie, no within-subject variability at all).
Sensitivity was defined as the ratio of the estimated effect of the active drug over the placebo divided by the estimated within-subject SD. The within-subject SD is based on the "usual" SD of the three non-ß-blocker observations for each subject pooled across all subjects. Ninety-five percent confidence intervals for sensitivity were used to determine if there was a significant "intervention" effect, ie, whether the active treatment was significantly different from the placebo intervention. The reason why this measure of sensitivity was chosen was to allow an assessment of the effect of the intervention on an individual basis, not on a group basis. For example, a sensitivity ratio of 1.5 for a particular intervention means that the effect of the intervention is to change the average level of the variable by one-and-a-half times the variability in the measurement seen across (within) any individual. Thus, sensitivity ratios < 1.0 would be considered to be of limited value because the change in the variable is not very different from the variability in the measurement seen across (within) any individual. All three time points were used to examine in detail any systematic order of visit/learning effect.
The relationship between each symptomatic scale and physiologic variable is complicated because it may be influenced not only by differences among subjects but also by the effects of any therapy, intervention or, indeed, the cumulative effect of exercise through the effect of time into a test itself.
Accordingly, the strategy adopted was, for each combination of subjective scale and physiologic variable, to produce sample correlation coefficients for each individual on each visit. For each individual, these were pooled across visits by simply taking the median of the four sample correlations from that subject’s four visits. To summarize the overall or typical correlation for this subjective scale and physiologic variable, the median across all the individuals’ "pooled correlations" was taken.
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionThe Relationship Between the...ConclusionReferences |
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Sensitivity: The Borg scale was significantly better than the LS at 5.5 min and 7.25 min and, perhaps surprisingly, better than the VAS at 5.5 min (Table 3) .
Visit and Therapy Effects
The 7.25-min time point was selected to provide a detailed and
representative example of visit and therapy effects. Analysis of the
other time points has shown broadly similar results, and, to save
unnecessary duplication, 7.25 min was chosen because its results were
typical of the other time points. Using a generalized linear model,
point estimates were produced for the visit and therapy effects of each
subjective scale separately. Table 4
shows the estimated visit and therapy effects for both breathlessness
and general fatigue, respectively. It is important to remember that
these estimated effects are all relative to the grand mean (in the
sense that all visit effects sum to zero). If the analysis of variance
test of a visit effect proved to be significant for the particular
variable under question, a Bonferroni-based multiple-comparisons
procedure was used to assess where the significant differences, if any,
lay.
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All scales (VAS, Borg scale, and LS) showed a significant therapy effect. The therapy effect was generally quite a bit higher than any of the individual visit effects in all scales.
General Fatigue: The VAS showed significant visit effects, again decreasing through visits. Formally, visit two and visit three were significantly lower than visit one, and visit four was significantly lower than the other three visits. Visit one for the Borg scale was significantly higher than the other three visits which were not significantly different from each other. The LS showed no significant visit effect.
All scales (VAS, Borg scale, and LS) showed a significant therapy effect. Again, the therapy effects were much higher than any of the visit effects.
Physiologic Variables
Aerobic Power and Submaximal Relative Intensity:
The mean O2max of 56.5 ± 5.8
mL/kg/min reflects the high aerobic fitness level of this group of
recreationally active male subjects. The projected steady-state
relative intensity was 70% O2max,
and the measured mean percent O2max
for the R1 test was 71 ± 6%. The fact that there was no significant
difference between the minute 6 and minute 8 values on R1, R2, and
placebo for O2, carbon dioxide
output (CO2), and minute
ventilation (E) indicates that a steady state
was achieved in these treatments. The variables investigated were as
follows: E, O2,
CO2, frequency of breathing,
tidal volume (VT), and heart rate. Table 5
gives a flavor of the physiologic data and shows the values for R1, R2,
placebo, and active therapy for minute 7.25, suggesting that there
differences in some variables between the active therapy and other
treatments.
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E, the active therapy was significantly
higher than the other three interventions after minute 3; (2)
O2, the active therapy
was significantly lower than the other three interventions at all times
until the last 2 min; (3)
CO2, at minutes 1 and 2,
the active therapy was significantly lower, while at minute 8, it was
significantly higher than the other three interventions; (4) frequency
of breathing, after 2 min, the active therapy was significantly higher
than the other three interventions; (5) VT, at 2
min and 6 min, the active therapy was significantly higher than the
second reproducibility replicate only; and (6) heart rate, the active
therapy was significantly lower than the other three interventions at
all time points during exercise.
Visit and Therapy Effects
Only E and frequency of breathing produced
significant visit effects, although O2
was close to the significance borderline. Table 6
shows that there was a trend for most variables to decrease over time:
the variables tended to be highest in test one and decreased through
the remaining three visits.
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E,
O2, CO2,
frequency of breathing, heart rate, and VT are shown in
Table 7
.
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E,
O2,
CO2, frequency of breathing,
heart rate, and VT. For E,
O2,
CO2, and heart rate, and all
the subjective scales, overall pooled correlations were
> 0.90. A wide range in the minimum and maximum (individual
and pooled) visit correlations was found for all the subjective scales
and the physiologic variables. These findings indicate that there is a
very good correlation between the subjective scales and
E, O2,
CO2, frequency of breathing,
heart rate, and VT. For all three time points, all three subjective scales were significantly different at each time point except for the LS (breathlessness), which showed no change between the time points of 5.5 min and 7.25 min. The difference between 5.5 min and 7.25 min was 3.8 for the VAS (breathlessness). For VAS (general fatigue), the difference between 5.5 min and 7.25 min was 3.2. The Borg scale (breathlessness) was significantly higher (0.25) at 7.25 min compared to 5.5 min. On the Borg scale (general fatigue), the 7.25 min score was 0.22 higher than the 5.5 min score. On the LS (general fatigue), the 7.25 min value was 0.24 higher than the 5.5 min value. From 5.5 min to 7.25 min, the perception of breathlessness and general fatigue increased despite the fact that there was no change in a range of physiologic variables.
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Discussion |
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Several groups have shown that the VAS allows reproducible
measurement of breathlessness in the short term in both normal subjects
and patients.7
8
9
Wilson and Jones10
11
have
shown that Borg scale measurements of breathlessness are also
reproducible in both the short and long term. Due to different exercise
protocols and statistical methods of evaluation, it is impossible to
say from these studies whether one scale is more reproducible than the
other. There have, however, been no descriptions of the reproducibility
of LS measurements of breathlessness during exercise. In the only other
direct comparison of the repeatability of the VAS and the Borg scale,
Wilson and Jones10
reported that the Borg scale was more
reproducible over the short term (a 2- to 6-week period) than the VAS.
For this reason, and the fact that the Borg scale correlated more
closely with E, Wilson and Jones10
favored the Borg scale. These authors, however, made repeatability
measurements of the slope of the relationship between the
breathlessness score and E, and not on scores at
fixed time points, as was done in this study.
The VAS demonstrated significantly better sensitivity at 5.5 min and 7.25 min than the Borg scale. The LS tended to be higher than the Borg scale and the VAS higher than the LS, but there were no significant differences. Some studies have induced a greater degree of breathlessness using resistive loading and have found that the VAS and the Borg scale to be responsive to this type of intervention. El-Manshawi et al12 used the Borg scale to quantify the intensity of breathlessness associated with exercise and respiratory resistive loading. They found that the perception of breathlessness increased at any given workload with resistive loading. Using bronchodilator treatment in chronic obstructive airways disease patients, the VAS has been shown to be sensitive to change.13 In a comparison of the Borg 6–20 scale and the VAS, Muza et al14 reported that the VAS may be twice as sensitive an indicator of change than the Borg 6–20 scale, and that the VAS may be of particular value in measuring subtle differences in the sensation of respiratory effort. In the present study, the VAS was the most sensitive for detecting change in breathlessness following pharmacologic intervention, though it should be noted that this change was in a different direction (ie, increased symptom intensity) than in the study by Stark et al.13
General Fatigue:
In this study, the VAS tended to be the most reproducible scale. The
Borg scale tended to perform better than the LS but not as well as the
VAS. There appears to be limited information on the reproducibility of
general fatigue.
The Borg scale was clearly much more sensitive to change than the other two scales for general fatigue. It is unknown why the Borg scale was the most sensitive of the three scales. Furthermore, it is unclear why the Borg scale for general fatigue is much more sensitive than the Borg scale for breathlessness; ie, why is the Borg scale able to detect change so much better in general fatigue than with breathlessness? The fact that there is such a great difference in the performance of the Borg scale between breathlessness and general fatigue indicates that the subjects were able to differentiate between breathlessness and general fatigue.
Other studies15 16 17 18 have reported mixed findings on the ability of subjective scales to establish differences in the perception of fatigue. Explanations for these different findings may be attributed to the fact that a range of exercise intensities and exercise protocols have been employed and a variety of pharmacologic agents and regimens have been used to promote fatigue.
Comparison of Breathlessness/General Fatigue Differences and
Scales:
Reproducibility coefficients for breathlessness and general fatigue
were highest for the VAS throughout the three time points, but they
were only statistically significant at minute 5.5 for breathlessness.
Indeed, the reproducibility coefficients for breathlessness and general
fatigue follow a similar pattern. It could be hypothesized that the
subjects were unable to distinguish between the two symptoms. However,
all of the subjects reported that they could discriminate between
breathlessness and general fatigue. Instructions to the subjects were
clearly given before each test, and the subjects confirmed that they
could clearly differentiate between breathlessness and fatigue. It may
be expected that the VAS would be the most sensitive scale because it
offers finer adjustment. In breathlessness, this is the case; but
perhaps somewhat surprisingly for general fatigue, the Borg scale is
the most sensitive of the three scales. The variation in
responses between the various time points may be a result of varying
perceptions of sensations over time and the time to adapt to the level
of exercise.
It is speculated here that it is necessary for large changes in status to occur before subjects are likely to move to another point on the LS. If this were true, it would be anticipated that the LS would be very reproducible in similar conditions. However, any movement in a subject’s scores is likely to heavily "penalize" the LS scale because a change of one is equivalent to 20% of the range of possible scores. Word descriptors did not restrict the use of the LS because a score of four was given for LS (breathlessness and general fatigue) on the active therapy, R1, and placebo. Previous studies using 4-, 5-, and 7-point LSs have produced inconclusive results. Guyatt et al19 stated that a seven-point LS compared to a VAS did not result in a response difference. However, they concluded that the ease of administration of the LS and "the extent to which clinicians intuitively grasp its results" pointed to the use of the LS instead of VAS.
Comparison of the Visit and Therapy Effects:
The VAS (breathlessness and general fatigue) and LS (breathlessness)
showed a significant visit effect. These visit effects were small
compared to therapy effects, but were fairly large in comparison to the
absolute scores. Care has to be taken in the use of this protocol
because it has been shown that there is a visit effect for some scales.
Despite the fact that the therapy effect was much greater than the
visit effect, it is advisable to incorporate a run-in period when this
protocol is used.
Physiologic Variables:
E was increased from 3 to 8 min compared to
placebo. The increase in E during high-intensity
steady-state exercise during the later stages of the exercise bout is
in agreement with the literature that indicates that subjects need to
exercise at fairly high intensities before a significant increase in
E is found.20
21
22
23
An increase in plasma
potassium during exercise after ß-blockade, due to reduced re-uptake
in inactive tissues, has been found.24
This could result
in an increased ventilatory drive via the peripheral
chemoreceptors.25
Twentyman et al20
concluded
that the increase in E at the end of the 70% steady
state cannot be explained by depression of central or peripheral
ventilatory control by propranolol or changes in lung mechanics.
Twentyman et al20
suggested that the increase in
E in the latter stages of the 70%
O2max steady state was the
E responding to increased levels of lactic acid.
Airway resistance and lung mechanics are not usually influenced to any
great extent by propranolol at rest or during exercise in normal
subjects and cannot explain the increase in
E.26
On the active therapy, the frequency of breathing was significantly increased from minute 2 onwards, but there were only two time points when VT was lowered with propranolol. Joyner et al27 reported a small decrease in VT after nonselective blockade that was compensated by an increased frequency of breathing, whereas Pearson et al21 found that VT was increased with atenolol but not with propranolol.
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The Relationship Between the Subjective Scales and Physiologic Variables |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionThe Relationship Between the...ConclusionReferences |
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E, O2,
CO2, frequency of breathing,
heart rate, and VT. However, it must be stressed that a
high correlation does not necessarily imply a causal relationship. When
using VAS and Borg scales, a good correlation has been reported between
E and the perception of
breathlessness.10
14
However, it would be wrong to suggest
that the perception of breathlessness is simply a sensing of
E. With no increase in E,
O’Neill et al7
found that their subjects reported
a rise in breathlessness. Other studies suggest that
E per se is not the most important factor
impinging on breathlessness. The cause of an increase in
E and the time delay between an increase
in breathlessness and an increase in E
should be taken into consideration.28
29
In this study,
E remained stable between 5.5 min and 7.25
min in the R1, R2, and placebo treatments but rose by 4 L/min in the
active therapy. Despite the stability of all respiratory variables on
R1, R2, and placebo, the perception of breathlessness increased as
measured by the VAS and the Borg scale. The correlation between breathlessness (VAS) and frequency of breathing was 0.85 and 0.89 for the correlation between VT and the LS was (the highest correlations for frequency of breathing and VT). The findings of Chronos et al29 cast doubt on a direct linkage between frequency of breathing and VT with breathlessness. They found that there was no relationship between the changes in breathlessness and changes in frequency of breathing or VT.
General Fatigue:
All three scales showed very high correlations between
E, O2,
CO2, heart rate, and general
fatigue. A review by Carton and Rhodes30
reported that it
is E and frequency of breathing that are most
closely related to perception of effort. In this study, the
correlations for E and frequency of breathing and
the three scales were around 0.92 and 0.80, respectively. The fact that
there was no significant difference in E and
frequency of breathing between 5.5 min and 7.25 min in R1, R2, and
placebo, as well as the fact that the perception of general fatigue was
higher at 7.25 min compared to 5.5 min, suggests that the perception of
general fatigue is not directly linked to E and
frequency of breathing.
This study found a high correlation between heart rate and the
subjective scales. A good relationship has been reported between the
rating of perceived exertion and heart rate,31
but
a causal link has been rejected. The fact that heart rate can be
changed at a given O2 with no
effect on the rate of perceived exertion substantiates this
hypothesis.32
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Footnotes |
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CO2 = carbon
dioxide output; E = minute ventilation;
O2 = oxygen uptake;
O2max = maximum oxygen uptake;
VT = tidal volume Received for publication September 23, 1997. Accepted for publication June 8, 1999.
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionThe Relationship Between the...ConclusionReferences |
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 M A Dentener, E C Creutzberg, A M W J Schols, A Mantovani, C van`t Veer, W A Buurman, and E F M Wouters Systemic anti-inflammatory mediators in COPD: increase in soluble interleukin 1 receptor II during treatment of exacerbations Thorax, September 1, 2001; 56(9): 721 - 726. [Abstract] [Full Text] [PDF]
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