Title
Highs and lows of sympathetic neurocardiovascular transduction: influence of altitude acclimatization and adaptation
Date Issued
24 November 2020
Access level
open access
Resource Type
journal article
Author(s)
Berthelsen L.F.
Fraser G.M.
Simpson L.L.
Vanden Berg E.R.
Busch S.A.
Steele A.R.
Meah V.L.
Lawley J.S.
Gasho C.
Willie C.K.
Tymko M.M.
Ainslie P.N.
Stembridge M.
Moore J.P.
Steinback C.D.
Publisher(s)
American Physiological Society
Abstract
High-altitude (>2,500 m) exposure results in increased muscle sympathetic nervous activity (MSNA) in acclimatizing lowlanders. However, little is known about how altitude affects MSNA in indigenous high-altitude populations. Additionally, the relationship between MSNA and blood pressure regulation (i.e., neurovascular transduction) at high-altitude is unclear. We sought to determine 1) how high-altitude effects neurocardiovascular transduction and 2) whether differences exist in neurocardiovascular transduction between low- and high-altitude populations. Measurements of MSNA (microneurography), mean arterial blood pressure (MAP; finger photoplethysmography), and heart rate (electrocardiogram) were collected in 1) lowlanders (n = 14) at low (344 m) and high altitude (5,050 m), 2) Sherpa highlanders (n = 8; 5,050 m), and 3) Andean (with and without excessive erythrocytosis) highlanders (n = 15; 4,300 m). Cardiovascular responses to MSNA burst sequences (i.e., singlet, couplet, triplet, and quadruplet) were quantified using custom software (coded in MATLAB, v.2015b). Slopes were generated for each individual based on peak responses and normalized total MSNA. High altitude reduced neurocardiovascular transduction in lowlanders (MAP slope: high altitude, 0.0075 ± 0.0060 vs. low altitude, 0.0134 ± 0.080; P = 0.03). Transduction was elevated in Sherpa (MAP slope, 0.012 ± 0.007) compared with Andeans (0.003 ± 0.002, P = 0.001). MAP transduction was not statistically different between acclimatizing lowlanders and Sherpa (MAP slope, P = 0.08) or Andeans (MAP slope, P = 0.07). When resting MSNA is accounted for (ANCOVA), transduction was inversely related to basal MSNA (bursts/minute) independent of population (RRI, r = 0.578 P < 0.001; MAP, r = -0.627, P < 0.0001). Our results demonstrate that transduction is blunted in individuals with higher basal MSNA, suggesting that blunted neurocardiovascular transduction is a physiological adaptation to elevated MSNA rather than an effect or adaptation specific to chronic hypoxic exposure. NEW & NOTEWORTHY This study has identified that sympathetically mediated blood pressure regulation is reduced following ascent to high-altitude. Additionally, we show that high altitude Andean natives have reduced blood pressure responsiveness to sympathetic nervous activity (SNA) compared with Nepalese Sherpa. However, basal sympathetic activity is inversely related to the magnitude of SNA-mediated fluctuations in blood pressure regardless of population or condition. These data set a foundation to explore more precise mechanisms of blood pressure control under conditions of persistent sympathetic activation and hypoxia.
Start page
H1240
End page
H1252
Volume
319
Issue
6
Language
English
OCDE Knowledge area
Sistema cardiaco, Sistema cardiovascular
Scopus EID
2-s2.0-85096887172
PubMed ID
Source
American Journal of Physiology - Heart and Circulatory Physiology
ISSN of the container
03636135
Sponsor(s)
This research has been funded by the Natural Sciences and Engineering Research Council of Canada (NSERC; GMF RGPIN 05205, CDS RGPIN 06637, PNA RGPIN 0821-01), the Physiological Society Research Grant Scheme (M.S.), Santander Mobility Fund (L.L.S., M.S., J.P.M.), and Gilchrist Educational Trust (L.L.S., J.P.M., M.S.). C.D.S. is funded by a Heart and Stroke Foundation of Canada Joint National and Alberta New Investigator Award (HSFC NNIA Steinback). P.N.A. is a Tier II Canada Research Chair in Cerebrovascular Physiology (950-230970).
Sources of information: Directorio de Producción Científica Scopus