Sympathetic activity during passive heat stress in healthy aged humans

Daniel Gagnon, Zachary J. Schlader, Craig G. Crandall

Research output: Contribution to journalArticle

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Abstract

Cardiovascular adjustments during heat stress are generally attenuated in healthy aged humans, which could be due to lower increases in sympathetic activity compared to the young. We compared muscle sympathetic nerve activity (MSNA) between 11 young (Y: 28 ± 4 years) and 10 aged (A: 70 ± 5 years) subjects prior to and during passive heating. Furthermore, MSNA responses were compared when a cold pressor test (CPT) and lower body negative pressure (LBNP) were superimposed upon heating. Baseline MSNA burst frequency (Y: 15 ± 4 vs. A: 31 ± 3 bursts min<sup>-1</sup>, P ≤ 0.01) and burst incidence (Y: 26 ± 8 vs. A: 50 ± 7 bursts (100 cardiac cycles (CC))<sup>-1</sup>, P ≤ 0.01) were greater in the aged. Heat stress increased core temperature to a similar extent in both groups (Y: +1.2 ± 0.1 vs. A: +1.2 ± 0.0°C, P = 0.99). Absolute levels of MSNA remained greater in the aged during heat stress (burst frequency: Y: 47 ± 6 vs. A: 63 ± 11 bursts min<sup>-1</sup>, P ≤ 0.01; burst incidence: Y: 48 ± 8 vs. A: 67 ± 9 bursts (100 CC)<sup>-1</sup>, P ≤ 0.01); however, the increase in both variables was similar between groups (both P ≥ 0.1). The CPT and LBNP further increased MSNA burst frequency and burst incidence, although the magnitude of increase was similar between groups (both P ≥ 0.07). These results suggest that increases in sympathetic activity during heat stress are not attenuated in healthy aged humans.

Original languageEnglish (US)
Pages (from-to)2225-2235
Number of pages11
JournalJournal of Physiology
Volume593
Issue number9
DOIs
StatePublished - May 1 2015

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Hot Temperature
Muscles
Lower Body Negative Pressure
Heating
Incidence
Temperature

ASJC Scopus subject areas

  • Physiology

Cite this

Sympathetic activity during passive heat stress in healthy aged humans. / Gagnon, Daniel; Schlader, Zachary J.; Crandall, Craig G.

In: Journal of Physiology, Vol. 593, No. 9, 01.05.2015, p. 2225-2235.

Research output: Contribution to journalArticle

Gagnon, Daniel ; Schlader, Zachary J. ; Crandall, Craig G. / Sympathetic activity during passive heat stress in healthy aged humans. In: Journal of Physiology. 2015 ; Vol. 593, No. 9. pp. 2225-2235.
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