Inspiratory resistive loading does not increase sympathetic tone in COPD.
OBJECTIVE
Neurohumoral activation has been shown to be present in patients with chronic obstructive pulmonary disease (COPD). The increase in respiratory muscle work might be responsible for the observed elevation of sympathetic tone via a respiratory muscle ergoreflex in these patients. The aim of this study is to investigate whether moderately increasing inspiratory resistive loading will impact on sympathetic activity in healthy subjects and COPD patients.


METHODS
Efferent muscle sympathetic nerve activity, blood pressure, heart rate and respiratory movements were continuously measured in 15 patients and 15 healthy control subjects. In order to increase work of breathing as evaluated by the tension-time index, inspiratory resistive loading was performed while patients were breathing through a spirometer.


RESULTS
At baseline, sympathetic nerve activity was significantly elevated in patients. Resistive loading increased work of breathing (tension-time index) by roughly 110% (COPD) and 130% (controls) but did not significantly alter blood gases or sympathetic activity in either group.


CONCLUSIONS
Doubling the work of breathing does not affect sympathetic activation in COPD patients or healthy control subjects. Thus in COPD the respiratory muscle ergoreflex does not seem to play a major role in sympathoexcitation.
Raupach
Tobias
T
Department of Cardiology and Pneumology, University Hospital Goettingen, Robert-Koch-Strasse 40, D-37075 Goettingen, Germany. raupach@med.uni-goettingen.de
Bahr
Florian
F
Herrmann
Peter
P
Lüthje
Lars
L
Hasenfuss
Gerd
G
Andreas
Stefan
S
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000403:Airway Resistance / Q000502:physiology*; D000704:Analysis of Variance; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D007320:Inspiratory Capacity; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012132:Respiratory Muscles / Q000503:physiopathology*; D013147:Spirometry; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D014939:Work of Breathing / Q000502:physiology*