Background: Enhanced hypercapnic chemoreflex in chronic heart failure could modulate sympathetic nerve activity in a different manner depending on the severity of heart failure. This study was designed to evaluate the dynamic aspects of sympathoexcitation caused by central hypercapnic chemoreflex in patients with chronic heart failure.
Methods and results: In 21 patients with chronic heart failure, wavelet analysis was applied to elucidate the spectral components of muscle sympathetic nerve activity (MSNA) and instantaneous ventilation during hypercapnic chemoreceptor stimulation. Hypercapnia increased MSNA (83+/-8 versus 29+/-9 %, P<.01) and ventilation (209+/-27 versus 190+/-21%, P<.05) more in 12 symptomatic patients than in 9 asymptomatic patients. This hypercapnic chemoreflex exerted a greater influence on the sympathetic limb than on the ventilatory limb in the symptomatic patients. The wavelet analysis revealed that the within-breath sympathoinhibition in the symptomatic patients was attenuated as compared with that in the asymptomatic patients (0.33+/-0.03 vs. 0.44+/-0.04, P<.05).
Conclusions: The enhanced chemoreflex sympathetic drive and relative attenuation of ventilatory sympathoinhibition could contribute to exaggerated sympathoexcitation in patients with heart failure when they are exposed to carbon dioxide during exercise or sleep apnea.