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Communications to the Editor |

Testing for Exercise Limitation in Obstructive Lung DiseaseTesting for Exercise Limitation in Obstructive Lung Disease FREE TO VIEW

Marc Newton, MD; Katherine A. Webb, MSc; Denis E. O’Donnell, MD, FCCP
Author and Funding Information

Affiliations: Queen’s University Kingston, ON, Canada ,  Meakins-Christie Laboratories McGill University Montreal, QC, Canada



Chest. 1999;115(6):1755-1757. doi:10.1378/chest.115.6.1755-a
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In their recent article, Murariu and colleagues (October 1998)1report that exercise performance in patients with obstructive lung disease is likely linked to the degree of resting lung hyperinflation as indirectly measured by inspiratory capacity (IC). Certainly, there is increasing evidence that dynamic lung hyperinflation during exercise (as assessed by serial IC measurements) contributes to the intensity and quality of dyspnea, and thus exercise limitation in COPD.2,,3,,4 Furthermore, increases in dynamic IC have been shown to correlate well with improvement in dyspnea and exercise endurance following pharmacologic2,,3 and surgical volume reduction.5 The study by Murariu and colleagues is, however, the first to claim an association between the resting IC and exercise performance in patients with obstructive lung disease (COPD and asthma).

The authors report a correlation coefficient of 0.81 (p < 0.001) between maximal exercise power output (Ẇmax) and IC in 25 patients with mild COPD (FEV1, 0.68 ± 21) who had, on average, moderate exertional dyspnea (Borg 4 ± 1) and exercise curtailment Ẇmax (62 ± 29% predicted). There is, however, a significant confounding factor here that the authors did not correct for: the absolute Ẇmax and the IC would be expected to be linearly related, even in normal subjects. The predicted IC and Ẇmax are both functions of age, sex, and height. Simply stated, taller, younger male subjects would be expected to have high Ẇmax and IC, while shorter, older female subjects would have lower Ẇmax and IC. In fact, predicted Ẇmax is a linear equation of age, sex, and height.6 This explains the significant correlation between height and Ẇmax as reported by Murariu and colleagues (correlation coefficient, 0.61; p < 0.005).

To establish a causal relationship between reduced IC and diminished Ẇmax, both IC and Ẇmax should be normalized and expressed as percent predicted. In their article, Murariu and coworkers provided us with the respiratory function and Ẇmax data (reported as percent predicted) for all study subjects. When viewed in this way, the relationship is not as strong (Fig 1). In fact, the correlation coefficient is only 0.294 (p = 0.154).

In summary, it is not likely that a particular patient’s exercise limitation would be strongly predicted by a single static pulmonary function test. That is not to say that lung hyperinflation, and particularly dynamic hyperinflation during exercise, is not important in dyspnea causation and exercise limitation in many patients with COPD. However, spirometric testing does not obviate the need for direct cardiopulmonary exercise testing, which remains the best and only way to accurately evaluate exercise capacity.

Correspondence to: Marc Newton, MD, Division of Respiratory and Critical Care Medicine, Queen’s University, 102 Stuart St, Kingston, ON, Canada; e-mail: fmnewton@istar.ca

Figure Jump LinkFigure 1. Relationship between IC (percent predicted) and Ẇmax (percent predicted) in 25 patients with obstructive airways disease, compiled from data provided by Murariu et al.1Grahic Jump Location
Murariu, C, Ghezzo, H, Milic-Emili, J, et al (1998) Exercise limitation in obstructive lung disease.Chest114,965-968. [CrossRef]
 
O’Donnell, DE, Webb, KA Exertional breathlessness in patients with chronic airflow limitation: the role of lung hyperinflation.Am Rev Respir Dis1993;148,1351-1357. [CrossRef]
 
Belman, MJ, Botnick, WC, Shin, JW Inhaled bronchodilators reduce dynamic hyperinflation during exercise in patients with chronic obstructive pulmonary disease.Am J Respir Crit Care Med1996;153,967-975. [CrossRef]
 
O’Donnell, DE, Lam, M, Webb, KA Measurement of symptoms, lung hyperinflation and endurance during exercise in chronic obstructive pulmonary disease.Am J Respir Crit Care Med1998;158,1557-1565. [CrossRef]
 
Martinez, FJ, Montes de Oca, M, Whyte, RI, et al Lung-volume reduction improves dyspnea, dynamic hyperinflation and respiratory muscle function.Am J Respir Crit Care Med1997;155,1984-1990. [CrossRef]
 
Jones, NL, Makrides, L, Hitchcock, C, et al Normal standards for an incremental progressive cycle ergometer test.Am Rev Respir Dis1985;131,700-708
 

Testing for Exercise Limitation in Obstructive Lung Disease

To the Editor:

In normal subjects, there is a close association between maximal exercise power output (Ẇmax) and vital capacity, the variation coefficient (r2) amounting to 0.79.1-1 Nevertheless, in our patients with obstructive lung disease (OLD), the variation coefficient of Ẇmax to FVC was substantially weaker than that of inspiratory capacity (IC) (0.41 vs 0.66). Furthermore, in 21 patients with restrictive lung disease (RLD) who were included in our original manuscript, there was no significant correlation of Ẇmax to IC, though their exertional dyspnea and exercise curtailment were similar to those of the OLD patients. Thus, in OLD but not RLD patients, the resting IC is a better predictor of Ẇmax than either FVC or FEV1.

Although we argue that there is predictably a close association between Ẇmax and IC in OLD patients because of expiratory flow limitation, we do not state that “a particular patient’s exercise limitation can be strongly predicted by IC.” In fact, the r2 between Ẇmax and IC was only 0.66, reflecting substantial scatter of the data.

Prediction of Ẇmax and IC is a nettlesome problem in old individuals, such as our OLD population. In fact, there are many predictive equations for Ẇmax, each giving a different value.1-1 Furthermore, the predicted normal values of IC are obtained as the difference between predicted total lung capacity and FRC. Thus, assessment of the relationship of Ẇmax (% predicted) to IC (% predicted) may be problematic, particularly in small numbers of patients with moderate exercise limitation. In 34 OLD patients with a more marked decrease in Ẇmax (39% predicted on average), a significant correlation was found both between the absolute and the predicted values of Ẇmax and IC, with IC being the only significant contributor to Ẇmax (O. Diaz Patiño, MD, C. Lisboa, MD, J. Milic-Emili, MD; unpublished observations, July 1998).

In conclusion, we think that resting IC, the Cinderella of lung function testing, not only provides useful information about the effects of bronchodilators1-2 and surgical treatment1-3 on hyperinflation in OLD patients, but it also gives a useful estimate of a patient’s exercise capacity. If the actual Ẇmax in a given OLD patient is lower than that predicted by our regression equation, it is likely that the patient should benefit substantially by exercise rehabilitation because the exercise performance is probably mostly limited by mechanisms other than lung function impairment.

Correspondence to: Joseph Milic-Emili, MD, Meakins Christie Laboratories, McGill University, 3626 St. Urbain Street, Montreal QC H2X 2P2, Canada; e-mail: milic@meakins.lan.mcgill.ca

References
Jones, NJ Clinical exercise testing 4th ed.1997,243 WB Saunders. Philadelphia, PA:
 
Tantucci, C, Duguet, A, Similowski, T, et al Effect of salbutamol on dynamic hyperinflation in chronic obstructive pulmonary disease patients.Eur Respir J1998;12,799-804. [CrossRef]
 
Boczkowski, J, Murciano, D, Pichot, M-H, et al Expiratory flow limitation in stable asthmatic patients during resting breathing.Am J Respir Crit Care Med1997;156,752-757. [CrossRef]
 

Figures

Figure Jump LinkFigure 1. Relationship between IC (percent predicted) and Ẇmax (percent predicted) in 25 patients with obstructive airways disease, compiled from data provided by Murariu et al.1Grahic Jump Location

Tables

References

Murariu, C, Ghezzo, H, Milic-Emili, J, et al (1998) Exercise limitation in obstructive lung disease.Chest114,965-968. [CrossRef]
 
O’Donnell, DE, Webb, KA Exertional breathlessness in patients with chronic airflow limitation: the role of lung hyperinflation.Am Rev Respir Dis1993;148,1351-1357. [CrossRef]
 
Belman, MJ, Botnick, WC, Shin, JW Inhaled bronchodilators reduce dynamic hyperinflation during exercise in patients with chronic obstructive pulmonary disease.Am J Respir Crit Care Med1996;153,967-975. [CrossRef]
 
O’Donnell, DE, Lam, M, Webb, KA Measurement of symptoms, lung hyperinflation and endurance during exercise in chronic obstructive pulmonary disease.Am J Respir Crit Care Med1998;158,1557-1565. [CrossRef]
 
Martinez, FJ, Montes de Oca, M, Whyte, RI, et al Lung-volume reduction improves dyspnea, dynamic hyperinflation and respiratory muscle function.Am J Respir Crit Care Med1997;155,1984-1990. [CrossRef]
 
Jones, NL, Makrides, L, Hitchcock, C, et al Normal standards for an incremental progressive cycle ergometer test.Am Rev Respir Dis1985;131,700-708
 
Jones, NJ Clinical exercise testing 4th ed.1997,243 WB Saunders. Philadelphia, PA:
 
Tantucci, C, Duguet, A, Similowski, T, et al Effect of salbutamol on dynamic hyperinflation in chronic obstructive pulmonary disease patients.Eur Respir J1998;12,799-804. [CrossRef]
 
Boczkowski, J, Murciano, D, Pichot, M-H, et al Expiratory flow limitation in stable asthmatic patients during resting breathing.Am J Respir Crit Care Med1997;156,752-757. [CrossRef]
 
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