Chest wall volume regulation during exercise in COPD patients with GOLD stages II to IV

The present study investigated how end-expiratory ribcage and abdominal volume regulation during exercise is related to the degree of dynamic chest wall hyperinflation in patients with different spirometric severity of chronic obstructive pulmonary disease (COPD) based on the Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification.

In total, 42 COPD patients and 11 age-matched healthy subjects were studied during a ramp-incremental cycling test to the limit of tolerance (Wpeak). Volume variations of the chest wall (at end expiration (EEVcw) and end inspiration) and its compartments (ribcage (Vrc) and abdominal (Vab)) were computed by optoelectronic plethysmography.

At Wpeak, only patients in GOLD stages III and IV exhibited a significant increase in EEVcw (increase of 454±509 and 562±363 mL, respectively). These patients did not significantly reduce end-expiratory Vab, whereas patients in GOLD stage II resembled healthy subjects with significantly reduced end-expiratory Vab (decrease of 287±350 mL). In patients, the greater the increase in EEVcw at Wpeak, the smaller the reductions in end-expiratory Vab and the greater the increase in end-expiratory Vrc.

In chronic obstructive pulmonary disease patients with different spirometric disease severity, greater degrees of exercise-induced dynamic chest wall hyperinflation were accompanied by lower degrees of end-expiratory abdominal volume displacement and larger increases in end-expiratory ribcage volume.

Exercise-induced dynamic hyperinflation refers to the temporary increase in end-expiratory lung volume above the baseline value that takes place not only in patients with moderate and severe chronic obstructive pulmonary disease (COPD) 1, 2 but also in patients with mild COPD 3, thereby limiting their exercise tolerance. Therapeutic interventions, such as bronchodilators 4, 5, oxygen supplementation 6, 7 and rehabilitative exercise training 8, 9 improve exercise tolerance by reducing the degree of dynamic hyperinflation. Measurement of operational lung volumes is therefore crucial in order to evaluate the effectiveness of these therapeutic interventions. To this end, optoelectronic plethysmography (OEP) has become a very useful method because it assesses breath-by-breath volume variations of the total chest wall and its compartments during exercise, i.e. ribcage and abdominal 1, 4, 9, 10.

Two recent studies by Aliverti et al. 4 and Georgiadou et al. 9 investigated the effects of bronchodilators and exercise training, respectively, on the chest wall volume regulation during exercise, using the OEP method. They concluded that the changes seen in exercise-induced chest wall hyperinflation after these interventions were almost exclusively attributable to changes of the abdominal and not the ribcage compartmental volumes. Interestingly, in the study by Georgiadou et al. 9, the training-induced reduction in end-expiratory abdominal volume was significantly correlated with the improvement in exercise tolerance.

In addition, it has been documented that patients who progressively hyperinflate during exercise are not effective in reducing their end-expiratory abdominal volume, whereas those who delay or even avoid increasing end-expiratory chest wall volume (EEVcw) with increasing exercise intensity exhibit significant reductions in end-expiratory abdominal volume 1, 10. Furthermore, in a recent study documenting reductions in exercise-induced chest wall hyperinflation after bronchodilator therapy, the essential difference between those patients who improved their exercise tolerance (improvers) and those who did not (nonimprovers) was in the degree of end-expiratory abdominal volume change; it was suggested that there was a different degree of expiratory muscle recruitment between improvers and nonimprovers 4. Earlier reports on different patterns of expiratory muscle recruitment in patients with COPD were controversial 11, 12. Potter et al. 11 suggested that in some patients, excessive recruitment of expiratory muscles during exercise may lead to dynamic airway compression, thus limiting expiratory flow, whereas Leaver and Pride 12 maintained that expiratory transthoracic pressures meet but do not exceed the critical closure pressure during exercise in COPD.

Based on the previous studies, it is apparent that the pattern of end-expiratory dynamic chest wall hyperinflation and its modulation during exercise depends on the regulation of end-expiratory abdominal volume 1, 4, 9, 10. As previous studies 9, 10 have suggested, the likelihood of exhibiting dynamic chest wall hyperinflation during exercise increases with increasing lung disease severity, manifested by the greater degrees of resting airway obstruction 9, 10 and expiratory flow limitation 2, 3. The present authors therefore reasoned that in COPD patients with different lung disease severity, greater degrees of exercise-induced dynamic chest wall hyperinflation would be accompanied by lesser reductions in end-expiratory abdominal volume. The purpose of the present study was therefore to determine how end-expiratory abdominal volume regulation during exercise is related to the degree of dynamic chest wall hyperinflation in patients with different spirometric severity of COPD based on Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification.