Efficiency of neural drive during exercise in patients with COPD and healthy subjects.
BACKGROUND
It is unknown whether efficiency of neural drive as expressed by a ratio of ventilation to the diaphragm electromyogram (EMGdi) in patients with COPD differs from that of healthy subjects during exercise and whether maximal neural drive is exhibited at the point of exercise termination.


METHODS
We studied 12 male patients with COPD (mean ± SD age, 62.8 ± 10.3 years; FEV(1), 28.1 ± 10.2% predicted) and 12 age- and sex-matched healthy subjects (age, 61.1 ± 7.2 years, FEV(1), 101.5 ± 11.9% predicted). EMGdi was recorded from a multipair esophageal electrode during a constant work (80% of maximal oxygen consumption derived from a previous incremental exercise test) treadmill exercise. Minute ventilation and oxygen consumption were also measured.


RESULTS
Root mean square (RMS) of the EMGdi increased initially and reached a plateau at submaximal drive during constant load exercise in both patients with COPD and healthy subjects. The ratio of ventilation to EMGdi remained stable during exercise in healthy subjects from beginning to the end (100% ± 70% at the beginning and 100% ± 39% at the end, P > .05), whereas the ratio decreased gradually during exercise in patients with COPD (from 85% ± 66% to 42% ± 13%, P < .05).


CONCLUSIONS
Efficiency of neural drive decreases in patients with COPD during treadmill exercise. Neural respiratory drive reached a submaximal plateau during constant load exercise in both healthy subjects and patients with COPD, indicating that it may not be the only factor determining exercise capacity.
Qin
Yin-Yin
YY
State Key Laboratory of Respiratory Disease, Guangzhou 510120, China. ym3698@yahoo.com.cn
Steier
Joerg
J
Jolley
Caroline
C
Moxham
John
J
Zhong
Nan-Shan
NS
Luo
Yuan-Ming
YM
D000368:Aged; D002245:Carbon Dioxide / Q000378:metabolism; D016022:Case-Control Studies; D003964:Diaphragm / Q000502:physiology*; D004567:Electrodes, Implanted; D004576:Electromyography / Q000379:methods*; D005080:Exercise Test / Q000379:methods*; D005652:Functional Residual Capacity; D006801:Humans; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010101:Oxygen Consumption / Q000502:physiology; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis*; D012016:Reference Values; D012129:Respiratory Function Tests; D012137:Respiratory System / Q000503:physiopathology*; D012720:Severity of Illness Index; D014109:Total Lung Capacity
D002245:Carbon Dioxide