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1 Division of Cardiology, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, Hershey 17033; 2 Lebanon Veterans Affairs Medical Center Lebanon, Pennsylvania 17042; and 3 Keesler Medical Center, Keesler Air Force Base, Mississippi 39534
Obstructive apnea and voluntary breath holding are associated
with transient increases in muscle sympathetic nerve activity (MSNA)
and arterial pressure. The contribution of changes in blood flow
relative to the contribution of changes in vascular resistance to the
apnea-induced transient rise in arterial pressure is unclear. We
measured heart rate, mean arterial blood pressure (MAP), MSNA (peroneal
microneurography), and femoral artery blood velocity (VFA, Doppler) in humans during voluntary
end-expiratory apnea while they were exposed to room air, hypoxia
(10.5% inspiratory fraction of O2), and hyperoxia (100%
inspiratory fraction of O2). Changes from baseline of leg
blood flow (
) and vascular resistance (R) were estimated from
the following relationships:
VFA, corrected for the heart rate, and R
MAP/
. During apnea, MSNA rose; this rise in MSNA was followed by a rise in MAP, which peaked a
few seconds after resumption of breathing. Responses of MSNA and MAP to
apnea were greatest during hypoxia and smallest during hyperoxia
(P < 0.05 for both compared with room air breathing). Similarly, apnea was associated with a decrease in
and an
increase in R. The decrease in
was greatest during hypoxia and
smallest during hyperoxia (
25 ± 3 vs.
6 ± 4%,
P < 0.05), and the increase in R was the greatest
during hypoxia and the least during hyperoxia (60 ± 8 vs. 21 ± 6%, P < 0.05). Thus voluntary apnea is associated with vasoconstriction, which is in part mediated by the sympathetic nervous system. Because apnea-induced vasoconstriction is most intense
during hypoxia and attenuated during hyperoxia, it appears to depend at
least in part on stimulation of arterial chemoreceptors.
obstructive sleep apnea; muscle sympathetic nerve activity; arterial chemoreflex
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