Terziyski, Kiril MD; Marinov, Blagoi MD, PhD; Hodgev, Vladimir MD, PhD; Tokmakova, Maria MD, PhD; Kostianev, S. MD, PhD, DMSc
Multiple factors that influence oxygen uptake (V̇O2) or metabolic equivalents (METs), including cardiac function, musculoskeletal status, body composition, motivation, and tolerance of discomfort, affect perception of exertion.1 Oxygen uptake may also be increased in different disease states and has a distinctive impact on quality of life.2 Thus, the measure is commonly used in the assessment of rehabilitation and therapeutic interventions evaluating new drugs,3 and in referral for transplantation programs.1
However, because of the complex nature of exertion, perception does not always correlate with objective measures and functional capacity. Dissociation between exertional symptoms and cardiovascular hemodynamics, skeletal muscle dysfunction, and lung impairment has been documented by Wilson et al1 in patients with heart failure. Similar results in patients with chronic obstructive pulmonary disease (COPD) were found by Oga et al.4 These authors reported a weak correlation between exertion, assessed by the Borg score (Borg CR-10),5 and pulmonary function, exercise indices, health status, and psychological status, when analyzed individually. Although the Borg Rating of Perceived Exertion is the gold standard in the assessment of exercise perception, it represents only a subjective evaluation of exertion at peak workloads. Numerous disease states may prevent patients from reaching expected physiologic peak levels of exertion. Therefore, a meaningful way of standardizing the rating of perceived exertion at the end of exercise test would seem valuable for clinical practice.
The resting MET is defined as the energy utilized at rest while sitting quietly6 and is approximately 3.5 mL·kg-1.min-1. Exercise level is often expressed in multiples of resting metabolism, that is, METs. We believe that this parameter provides a more specific expression of individual levels of exertion in gauging exercise intensity. In addition, using METs instead of peak oxygen uptake (V̇O2peak) standardizes the equation in respect to body weight.
Standardized peak exercise perception score (SPEPS) is an index derived from the following equation: SPEPS= Borg/METs, where Borg is the Borg CR-10 at maximal exercise intensity and METs represent maximal METs values. The purpose of the study was to assess the validity of SPEPS in patients with COPD, CHF, and controls and to examine its applicability for evaluation of exercise training outcomes.
Prior to inclusion in the study, all patients were explained the associated risks and benefits and written informed consent was obtained. Procedures used in this study complied with the declaration of Helsinki and were approved by the Institutional Ethics Committee at the Medical University of Plovdiv.
Seventeen patients with chronic heart failure (CHF) (New York Heart Association [NYHA] II and III functional class; ejection fraction [EF]= 31 ± 14%), 16 COPD patients (forced expiratory volume in 1 second [FEV1%]= 51 ± 14%), and 16 age- and body mass index (BMI)–matched controls formed the primary study group. To test the effect of exercise training on SPEPS, we also recruited an additional 30 ambulatory patients with stable CHF (NYHA II–III). Twenty of these subjects were randomized to 8 weeks of supervised endurance exercise training (EET), forming CHF-EET group, and the rest (n = 10) formed the nontraining (NT) group. Randomization of CHF patients was accomplished by consecutive order of appearance, irrespective of any patient characteristics. Patients from the NT group were left to maintain their usual physical activity. All participants were clinically stable for at least 1 month prior to the study. Patients having an acute or chronic illness that may have impaired exercise performance, except for the primary diagnosis (CHF or COPD), were excluded from the study. Patients treated with β-blockers in the last 10 days prior to enrollment were also excluded.
Lung function measurements were performed in a laboratory compliant with American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines.7 Spirometry (the highest values from the best of at least 3 acceptable efforts) for forced vital capacity and FEV1, diffusion capacity (mean of 2 single-breath measurements), maximal inspiratory pressure from residual volume (PImax), and maximal expiratory pressure from total lung capacity (PEmax) (the best from at least 3 measurements) were measured using MasterScreen Diffusion (E Jaeger, Wuerzburg, Germany). All measurements were performed in a seated position with a nose clip. Predicted values for lung function parameters were calculated according to ERS.8
Echocardiographic assessment of left ventricle function was performed (Hewlett Packard PSonos 2500, Andover, Massachusetts) according to a standardized protocol. Left ventricular volumes were estimated by the area-length method (volume= 0.85 × area2/length) and an echocardiographic EF was calculated [EF= (diastolic volume × systolic volume)/diastolic volume]. A 6-minute walking test (6MWT)9 and symptom-limited incremental exercise tests were performed in all the participants. Exercise tests were performed on a motor-driven, electronically controlled treadmill by utilizing a standard Bruce protocol.10 Patients participating in the EET program (substudy) were assigned to an initial symptom limited ramp cardiopulmonary exercise test (CPET) on an electronically braked cycle ergometer (Ergometrics 900, Ergoline, Bitz, Germany). Throughout these exercise tests, gas exchange variables were determined with an online computerized system CardiO2 (MedGraphics, St Paul, Minnesota). Twelve-lead electrocardiograms (ECG) were recorded every 3 minutes, and heart rate (HR), ECG, and O2 saturation (SpO2, Pulsox OP8, Minolta, Osaka, Japan) were monitored continuously. Blood pressure was measured automatically by the system-integrated cuff sphygmomanometer every 3 minutes.
The training program was individually adjusted for each patient in the CHF-EET group, based on the baseline CPET results. Training load corresponded to 50% of peak oxygen uptake from the initial test. Each training session lasted for 40 minutes, and patients were instructed to maintain a cycling frequency between 60 and 70 rpm. The duration of exercise training program was 8 weeks with 5 visits per week (40 sessions). After the completion of the training program, a final CPET was performed. The Minnesota Living with Heart Failure questionnaire (MQ)3 was completed by CHF-EET and NT groups at baseline and at the end of the study.
All values are expressed as mean ± SD. The results from maximal exercise, lung function measurements, and anthropometric variables were assessed using descriptive statistics, ANOVA, paired samples t test, and Spearman ρ correlation in SPSS for Windows (SPSS Inc, Chicago, Illinois). Paired samples t tests were used to compare patient primary exercise parameters, SPEPS, and quality of life before and after rehabilitation. ANOVA was applied in the comparisons of the 3 main groups (CHF, COPD, and controls) for anthropometric, spirometric and exercise parameters.
Cardiopulmonary variables (V̇O2, ventilation [V.E], HR) served as criterion variables and the SPEPS and Borg CR-10 as concurrent variables. Construct validity was established by correlating SPEPS with CR-10 Borg Score. The Borg Scale was the criterion metric, and the SPEPS was the conditional metric.11
Characteristics of the studied groups are shown in Table 1. Peak V̇O2 (mL·kg-1.min-1) was significantly lower for the CHF and COPD groups than for control: 18.8 ± 3.8 (CHF) versus 21.1 ± 5.1 (COPD) versus 29.9 ± 5.2 (control), P < .001. Exercise duration and 6MWT were also significantly lower in COPD and CHF patients in comparison with controls. No statistically significant differences were observed for these parameters between CHF and COPD patients.
The CHF group showed a higher Borg rating of perceived exertion than COPD patients and controls, while Borg ratings between the latter 2 groups did not differ significantly. SPEPS showed better discriminative ability resulting in significant differences between each group. As shown in Figure 1, patients with CHF reveal more scattered SPEPS values with wider extremes.
Correlations were calculated for complex samples including COPD, CHF, and controls (n = 49) groups. SPEPS showed strong positive correlation with the Borg rating (ρ= 0.763, P < .001) and strong negative correlation with METs (ρ= −0.778, P < .001). SPEPS correlated significantly and to a greater extent than the Borg rating, with the V.E/V.CO2AT (ventilatory equivalent for CO2 at the anaerobic threshold, AT) (ρ= 0.52, P < .01), and with the 6MWT (ρ= −0.56, P < .001). Of note, the 6MWT showed no significant correlation with Borg scores. SPEPS also correlated negatively with oxygen pulse (V̇O2/HR) (ρ= −0.394, P= .005). SPEPS showed a significant negative correlation with basic spirometric and diffusion parameters: FEV1 (ρ= −0.391, P= .006) and diffusion coefficient (DLCO; ρ= −0.391, P= .008). A significant negative correlation was also present with PImax values (ρ= −0.392; P= .018).
Fifteen of the 20 patients assigned to EET completed the entire program (age= 51.3 ± 9.7 years; BMI= 27.0 ± 3.1 kg·m-2; rest HR= 83.7 ± 14.6 beats · min-1; EF= 33.4 ± 6.4%; peak V̇O2= 1123 ± 365 mL.min-1). Seven of the 10 patients constituting the NT group were in the study at week 8. Subjects were matched by anthropometric, clinical, and functional parameters (n = 7; age= 53.6 ± 9.0 years; BMI= 26.6 ± 4.0 kg.m-2; rest HR= 86.0 ± 7.4 beats. min-1; EF= 34.3 ± 5.9%; peak V̇O2= 1165 ± 148 mL.min-1). Dropouts (5 patients from CHF-EET group and 3 patients from the NT group) did not differ from the remainder of the subjects with respect to baseline anthropometric and functional parameters. No subject discontinued the rehabilitation program for medical reasons; discontinuation in all cases was due to poor motivation to complete the entire program.
The basic outcome parameters in CHF-EET patients in regard to exercise training are shown on Table 2. Exercise training led to a clinically significant improvement of functional capacity. Objective improvement in physical capacity was represented by an increase in exercise duration time, peak V̇O2, V̇O2/kg, and oxygen uptake at AT (V̇O2AT). Significant reduction in subjective perception of exercise exertion was also detected by a decrease in Borg rating. SPEPS was significantly reduced after the completion of the training protocol. Among the investigated exercise parameters, SPEPS showed the most significant change after the rehabilitation program.
Baseline quality of life, assessed by MQ,3 did not differ significantly between the training (CHF-EET) and NT groups (35.3 ± 15.4 vs 41.2 ± 16.0). MQ scores decreased significantly after the training. Reduction in MQ scores and SPEPS values at the end of the training program showed a strong correlation (ρ= .748, P < .001; n = 22). Figure 2 shows a scatter plot of change in SPEPS (dSPEPS) versus change in MQ (dMQ) after 8 weeks of training in the CHF-EET group and the NT group. NT patients did not reveal significant change in SPEPS and MQ values over time in contrast to CHF-EET group.
No significant differences were observed in the NT group between the initial test and final test for objective and subjective CPET parameters: peak V̇O2 (mL·kg-1.min-1) (15.3 ± 2.3 vs 15.5 ± 2.8; SPEPS= 1.94 ± 0.68 vs 1.86 ± 0.74; P >.05 for both) and MQ score (35.3 ± 15.4 vs 31.9 ± 11.6; P= .150). The effects of exercise training on SPEPS in CHF-EET patients and respective values in NT subjects are presented on Figure 3. It is evident that exercise training resulted in a significant decrease of SPEPS values.
We found that SPEPS can effectively differentiate between the studied groups, being highest in CHF and lowest in the controls. SPEPS showed better discriminative capacity and higher correlation with basic rest and CPET parameters than the Borg score alone. SPEPS was significantly reduced after exercise training and therefore appears to be a useful tool for the evaluation of outcomes in rehabilitation programs.
Even though perception of effort is often great in patients, different exercise limitations may prevent them from reaching high Borg ratings. Therefore, we believe that effort perception should be interpreted in the context of corresponding V̇O2 level. Similar to other indices such as V̇O2/Watts,12 SPEPS is designed to express exertion by relative values for a given amount of exercise rather than end-test values, in order to avoid the aforementioned shortcoming. In the SPEPS formula, perceived effort is intentionally divided by METs rather than by other basic parameters of physical capacity (V̇O2, V̇O2/kg), because 1 MET represents the perceived effort increase corresponding to the metabolic increase from resting metabolism to various levels of energy expenditure. MET values for a number of household and recreational activities have been presented elsewhere6,13 and SPEPS may be easily calculated in these cases. The aforementioned arguments seem reasonable since SPEPS correlated much better with different rest and cardiopulmonary exercise parameters than the Borg rating, further implying its construct validity and improved discriminative ability at maximal exercise in different disease states.
Contrary to SPEPS results, we did not find significant correlations between the Borg rating with major objective indices, which is in concordance with the observations of Wilson et al1 in CHF patients. Similar results were reported among COPD patients by Oga et al,4 who found that the Borg score at the end of exercise correlated weakly with pulmonary function, exercise indices, health status, and psychological status. Contradictory results indicating a correlation between the Borg rating and FEV1 and PImax have also been reported.14 A possible explanation may be in the difference in sample size and/or the multifactorial nature of fatigue.4
Exercise results and exertion sensation are influenced by a complex myriad of factors and, logically, SPEPS is also expected to result from numerous determinants. Nevertheless, existing correlations with other parameters may shed light on the main influencing factors. The negative correlation of SPEPS with FEV1, VC%, DLCO, and V.E/V.CO2AT show significant contribution of pulmonary factors to worsening subjective perceptions during exercise, but cardiac factors are also important, as demonstrated by the correlation of SPEPS with V̇O2/HR. The correlation between PImax and SPEPS is not surprising since there is evidence that respiratory muscle strength is related to dyspnea sensation and that inspiratory muscle training alleviates dyspneic symptoms.15 Meanwhile 45% of the patients with COPD, asthma, and pulmonary hypertension cannot distinguish between dyspnea and fatigue because of the complex relationship of these factors.2 Inspiratory muscles play a key role in exercise perception in CHF patients as well, which has been demonstrated by the positive effects of inspiratory muscle training on exercise performance and tolerability.16 Therefore, cardiopulmonary and musculoskeletal influences on SPEPS are present, but psychological factors, which are of great importance in chronic fatigue,2 may also contribute.
All basic exercise parameters (exercise duration, absolute and relative maximal oxygen uptake, Borg rating) revealed significant improvement after completion of the exercise training protocol. These results are in concordance with previous studies, investigating the effect of different exercise rehabilitation on objective17 and subjective18 CPET parameters. Since a successful training program is related to an increase in physical capacity and a decrease in subjective evaluation of perceived exertion, it would be expected that SPEPS would significantly decrease after training and thus may also be used in the assessment of exercise training programs outcome. This was confirmed by our results. SPEPS even demonstrated itself to be the most sensitive among the investigated parameters in relation to rehabilitation outcomes.
The benefits of therapeutic and rehabilitation programs in CHF are often assessed by MQ score.3 In the present study, MQ also changed as a result of the exercise training and appeared to be as sensitive as SPEPS. However, with the strong correlation between the MQ and SPEPS observed here, it is clear that SPEPS has the ability to also detect changes in quality of life. In addition, comparable MQ and SPEPS improvement, as well as data regarding Borg reproducibility19 and small within-subject variation of V̇O2peak (METS),20 suggests a good level of SPEPS reproducibility. This hypothesis was confirmed by our results from the CHF control group patients, which showed no significant difference between the initial and final SPEPS values.
Limitations of the study should be mentioned. First, subjects consisted of only white males, which limits the applicability of findings to gender and race. The sample size was relatively small, although statistical significance was reached. Since SPEPS proved to be the most sensitive parameter to describe the effects of exercise training, it would be interesting to compare its values for everyday life activities before and after a rehabilitation program. How maximal values correlate with submaximal efforts including household and recreational activities was beyond the scope of the current analysis. An interesting direction for future research of SPEPS may be its predictive ability of morbidity and mortality in different patient groups.
Results suggest that SPEPS is a reliable new index in discriminating perceived exertion at the end of exercise test in different groups of patients (COPD and CHF), presenting both construct and concurrent validity. It is an important parameter for evaluation of the outcomes in training programs.
1. Wilson JR, Rayos G, Yeoh TK, Gothard P, Bak K. Dissociation between exertional symptoms and circulatory function in patients with heart failure. Circulation
2. Breslin E, van der Schans C, Breukink S, et al. Perception of fatigue and quality of life in patients with COPD. Chest
3. Rector TS, Cohn JN. Assessment of patient outcome with the Minnesota Living with Heart Failure questionnaire: reliability and validity during a randomized, double blind, placebo-controlled trial of pimobendan. Am Heart J
4. Oga T, Nishimura K, Tsukino M, Hajiro T, Mishima M. Dyspnoea with activities of daily living versus peak dyspnoea during exercise in male patients with COPD. Respir Med
5. Borg GA. Psychophysical bases of perceived exertion. Med Sci Sports Exerc
6. Jetté M, Sidney K, Blümchen G. Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity. Clin Cardiol
7. Miller MR, Hankinson J, Brusasco V, et al. Standardisation of spirometry. Eur Respir J
8. Quanjer PH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R, Yernault JC. Lung volumes and forced ventilatory flows. Report Working Party Standardization of Lung Function Tests, European Community for Steel and Coal. Official Statement of the European Respiratory Society. Eur Respir J Suppl
9. American Thoracic Society statement: guidelines for the six-minute walk test. Am J Respir Crit Care Med
10. Bruce RA, Blackmon JR, Jones JW, et al. Exercise testing in adult normal subjects and cardiac patients. Pediatrics
11. Utter A, Robertson R, Green JM, Suminski R, McAnulty S, Nieman D. Validation of the Adult OMNI scale of perceived exertion for walking/running exercise. Med Sci Sports Exerc
12. Wasserman K, Hansen JE, Sue DY, Stringer WW, Whipp BJ. Principles of Exercise Testing and Interpretation
. 4th ed. Baltimore, PA: Lippincott Williams & Wilkins; 2005.
13. Gunn S, Brooks A, Withers R, et al. Determining energy expenditure during some household and garden tasks. Med Sci Sports Exerc
14. Mancini DM, Henson D, La Manca J, Donchez L, Levine S. Benefit of selective respiratory muscle training on exercise capacity in patients with chronic congestive heart failure. Circulation
15. Beckerman M, Magadle R, Weiner M, Weiner P. The effects of 1 year of specific inspiratory muscle training in patients with COPD. Chest
16. Padula C, Yeaw E. Inspiratory muscle training: integrative review of use in conditions other than COPD. Res Theory Nurs Pract
17. Van Laethem C, Van De Veire N, De Backer G, et al. Response of the oxygen uptake efficiency slope to exercise training in patients with chronic heart failure. Eur J Heart Fail
18. Kulcu DG, Kurtais Y, Tur BS, Gülec S, Seckin B. The effect of cardiac rehabilitation on quality of life, anxiety and depression in patients with congestive heart failure. A randomized controlled trial, short-term results. Eura Medicophys
19. Wilson RC, Jones PW. Long-term reproducibility of Borg scale estimates of breathlessness during exercise. Clin Sci
20. Midgley AW, McNaughton LR, Carroll S. Effect of the V̇O2
time-averaging interval on the reproducibility of V̇O2
max in healthy athletic subjects. Clin Physiol Funct Imaging
© 2010 Lippincott Williams & Wilkins, Inc.