Multiple firing of single muscle vasoconstrictor neurons during cardiac dysrhythmias
in human heart failure.
Elam, Mikael, and Vaughan Macefield.
1Institute for Clinical Neuroscience, Department of Clinical Neurophysiology,
Sahlgren University Hospital, S-413 45 Göteborg, Sweden; and 2Prince of Wales
Medical Research Institute, Sydney, New South Wales 2031, Australia
APStracts 8:0244A, 2001.
Single vasoconstrictor nerve fibers in humans normally fire only once, but have the
capacity to fire as many as eight times, per cardiac interval. We recently demonstrated
that the mean firing frequency of individual vasoconstrictor fibers is more than doubled
in the sympathoexcitation associated with congestive heart failure (Macefield VG,
Rundqvist B, Sverrisdottir YB, Wallin BG, and Elam M. Circulation 100: 1708-1713,
1999). However, the propensity to fire only once per cardiac interval was retained. In the
present retrospective study, we tested the hypothesis that vasoconstrictor fibers fire more
than once per cardiac interval in response to transient sympathoexcitatory stimuli,
providing one mechanism for further increase of an already augmented sympathetic
discharge. Six patients with congestive heart failure (New York Heart Association
functional class II-IV; left ventricular ejection range 13-37, average 22%) were studied at
rest and during premature ectopic heartbeats. Analyzed for a total of 60 premature beats,
the average firing probability of 10 vasoconstrictor fibers increased from 61 to 80% in the
prolonged cardiac interval (i.e., reduced diastolic pressure) after premature beats. The
incidence of multiple within-burst firing increased markedly, two spikes being more
common than one. Our results illustrate two different mechanisms (increases in firing
probability and multiple within-burst firing), and indirectly indicate a third mechanism
(recruitment of previously silent fibers) for acute sympathoexcitatory responses.
Received 25 January 2001; accepted in final form 10 April 2001
APS Manuscript Number A75-1.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 18 June 2001