Regional chest wall volumes during exercise in chronic obstructive pulmonary disease.
BACKGROUND
Dynamic hyperinflation of the lungs impairs exercise performance in chronic obstructive pulmonary disease (COPD). However, it is unclear which patients are affected by dynamic hyperinflation and how the respiratory muscles respond to the change in lung volume.


METHODS
Using optoelectronic plethysmography, total and regional chest wall volumes were measured non-invasively in 20 stable patients with COPD (mean (SD) forced expiratory volume in 1 second 43.6 (11.6)% predicted) and dynamic hyperinflation was tracked breath by breath to test if this was the mechanism of exercise limitation. Resting ventilation, breathing pattern, symptoms, rib cage and abdominal volumes were recorded at rest and during symptom limited cycle ergometry. Pleural, abdominal, and transdiaphragmatic pressures were measured in eight patients.


RESULTS
End expiratory chest wall volume increased by a mean (SE) of 592 (80) ml in 12 patients (hyperinflators) but decreased by 462 (103) ml in eight (euvolumics). During exercise, tidal volume increased in euvolumic patients by reducing end expiratory abdominal volume while in hyperinflators tidal volume increased by increasing end inspiratory abdominal and rib cage volumes. The maximal abdominal pressure was 22.1 (9.0) cm H(2)O in euvolumic patients and 7.6 (2.6) cm H(2)O in hyperinflators. Euvolumic patients were as breathless as hyperinflators but exercised for less time and reached lower maximum workloads (p<0.05) despite having better spirometric parameters and a greater expiratory flow reserve.


CONCLUSIONS
Dynamic hyperinflation is not the only mechanism limiting exercise performance in patients with stable COPD. Accurate measurement of chest wall volume can identify the different patterns of respiratory muscle activation during exercise.
Dipartimento di Bioingegneria, Politecnico di Milano, Italy. andrea.aliverti@polimi.it
A
A
Aliverti
N
N
Stevenson
R L
RL
Dellacà
A
A
Lo Mauro
A
A
Pedotti
P M A
PM
Calverley
D000368:Aged; D015444:Exercise / Q000502:physiology*; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D011312:Pressure; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D035441:Thoracic Wall / Q000502:physiology; D014797:Vital Capacity / Q000502:physiology; D014939:Work of Breathing / Q000502:physiology