Paradoxical sympathetic nerve response to baroreceptor reflex activation

Spectral analysis revealed an enhancement of cardiac-related postganglionic sympathetic nerve discharge (SND) in response to elevated blood pressure in cats. Most of the enhancement occurred at blood-pressure levels above which coherence of SND to the arterial pulse at the frequency of the heart beat became maximal. This raises the possibility that the enhancement is due to mechanisms other than improved phase locking of SND to pulse-synchronous baroreceptor afferent nerve activity.