Inspiratory resistive loading does not increase sympathetic tone in COPD

Abstract

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. 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. 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. 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.