Muscle sympathetic reactivity to apneic and exercise stress in high-altitude Sherpa

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Author
Busch, Stephen
Simpson, Lydia
Sobierajski, Frances
Riske, Laurel
Ainslie, Philip
Willie, Chris
Stembridge, Mike
Moore, Jonathan
Steinback, Craig
Date
2020-01-08Acceptance date
2019-12-16
Type
Article
Publisher
American Physiological Society
ISSN
0363-6119
1522-1490 online
Metadata
Show full item recordAbstract
Lowland-dwelling populations exhibit persistent sympathetic hyperactivity at altitude that may
alter vascular function. High altitude populations, such as Sherpa, exhibit greater peripheral
blood flow in response to acute stress, suggesting Sherpas may exhibit lower sympathetic
activity and reactivity to stress than Lowlanders. Muscle sympathetic activity (MSNA;
microneurography) including frequency (bursts/min), incidence (bursts/100HB), amplitude (% of
max burst), was measured at rest in Lowlanders (n=14; age=27±6yrs) at 344m and following a 8-
9 days of graded ascent to 5050m. Sherpa (age=32±11yrs) were tested at 5050m (n=8).
Neurovascular reactivity (i.e., change in MSNA patterns) was measured during maximal end
expiratory apnea, isometric hand-grip (IHG; 30% maximal voluntary contraction for 2 minutes)
and post exercise circulatory occlusion (PECO; 3 minutes). Total normalized SNA (au/min) was
calculated over 10 cardiac cycles during baseline and pre-volitional apnea breakpoint. Lowlander
burst frequency (11±5 bursts/min to 30±7 bursts/min; Mean±SD; p<0.001) and burst incidence
(25±13 bursts/100HB to 53±15 bursts/100HB; p<0.001) increased at 5050m. In contrast, Sherpas
had lower burst frequency (23±11 bursts/min; p<0.05) and incidence (30±13 bursts/100HB;
p<0.05) at 5050m. MSNA increases in Lowlanders and Sherpa during apnea at 5050m were
significantly lower than Lowlanders at 344m (both P<0.05), with a possible sympathetic ceiling
reached in Lowlanders at 5050m. MSNA increased similarly during the IHG/PECO in
Lowlanders at 334m and 5050m altitude and Sherpa at 5050m. Sherpa demonstrate overall lower
sympathetic activity and reactivity during severe stress. This may be a result of improved
systemic hemodynamic function associated with evolutionary adaptations to permanent
residency at altitude.
Journal/conference proceeding
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology;
Citation
Busch, S.A., Simpson, L.L., Sobierajski, F., Riske, L., Ainslie, P.N., Willie, C.K., Stembridge, M., Moore, J.P. and Steinback, C.D. (2020) 'Muscle Sympathetic Reactivity to Apneic and Exercise Stress in High-Altitude Sherpa', American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.
Description
Article published in American Journal of Physiology-Regulatory, Integrative and Comparative Physiology on 08 January 2020, available at: https://doi.org/10.1152/ajpregu.00119.2019.
Sponsorship
Cardiff Metropolitan University (Grant ID: Cardiff Metropolian (Internal))
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