Abstract
We tested the hypothesis that breath-hold divers (BHD) attain higher level of sympathetic
activation than controls due to the duration of breath-hold rather than a different
recruitment strategy. In 6 control subjects and 8 BHD we measured muscle sympathetic
neural activity (MSNA) prior to and during functional residual capacity (FRC) and
total lung capacity (TLC) breath-holding. On a subset of subjects we applied a new
technique for the detection of action potentials (APs) in multiunit MSNA. Compared
with controls, BHD group had lower burst AP content (13±7 vs. 6±3 AP/burst; P=0.05) and number of active clusters (5±1 vs. 3±1 clusters/burst; P=0.05) at baseline. However, the overall sympathetic AP/unit-time was comparable between
the groups (131±105 vs. 173±152 AP/min; P=0.62) due to increased burst frequency in BHD group (20±4 bursts/min) vs. controls (13±3 bursts/min) (P=0.039). The achieved level in total MSNA during FRC breath-holds was higher in divers
(2298±780 vs. 1484±575 a.u./min; P=0.039). Total MSNA at the end of TLC breath-hold was comparable between the groups
(157±50 (controls) vs. 214±41 s (BHD); P=0.61). FRC and TLC breath-holds increased AP frequency, burst AP content and active
clusters/bursts in both groups but the response magnitude was determined by the type
of the breath-hold. The divers used fewer number of APs/burst and active clusters/burst.
In both groups breath-holds resulted in similar increases in MSNA which were reached
both by an increase in firing frequency and by recruitment of previously silent, larger
(faster conducting) sympathetic neurons, and possibly by repeated firing within the
same burst.
Keywords
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Article info
Publication history
Published online: June 06, 2011
Accepted:
May 17,
2011
Received in revised form:
May 10,
2011
Received:
January 10,
2011
Identification
Copyright
© 2011 Elsevier B.V. Published by Elsevier Inc. All rights reserved.
