Prolonged surges of baroreflex-resistant muscle sympathetic drive during periodic breathing.

We report unusual muscle sympathetic nerve activity (MSNA) in patients with Cheyne-Stokes respiration (CSR), one suffering congestive heart failure (CHF) and three with obstructive sleep apnea syndrome (OSAS). MSNA was recorded via a tungsten microelectrode in the peroneal nerve. Our index patient had severe CHF (LVEF 15%) and showed typical MSNA for this condition, with large sympathetic bursts occurring with every heart beat. However, superimposed on this pattern appeared broad surges of increased MSNA which lasted for 6-8 cardiac intervals. Although the cardiac rhythmicity of MSNA was preserved during these surges, the baroreceptor-mediated inhibition was never complete, resulting in an increase in baseline neural activity during the surge. Because their occurrence can be explained by the periodicity of the CSR and the estimated circulation time from the lung to the carotid bodies, we suggest that these surges in MSNA reflect a chemoreceptor-mediated increase in muscle vasoconstrictor drive.