Highs and Lows of Sympathetic Neuro-cardiovascular Transduction: Influence of Altitude Acclimatization and Adaptation
Vanden Berg, Emily
Busch, Stephen A.
Steele, Andrew R.
Meah, Victoria L.
Tymko, Michael M.
Ainslie, Philip N.
Moore, Jonathan P.
Steinback, Craig D.
American Physiological Society
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High-altitude (>2500m) exposure results in increased muscle sympathetic nervous activity (MSNA) in acclimatizing lowlanders. However, little is known about how altitude affects MSNA in 66 indigenous high-altitude populations. Additionally, the relationship between MSNA and blood 67 pressure regulation (i.e., neurovascular transduction) at high-altitude is unclear. We sought to 68 determine 1) how high-altitude effects neuro-cardiovascular transduction and 2) whether 69 differences exist in neuro-cardiovascular transduction between low and high-altitude 70 populations. Measurements of MSNA (microneurography), mean arterial blood pressure (MAP; 71 finger photoplethysmography), and heart rate (electrocardiogram) were collected in: I) 72 lowlanders (n=14) at low (344m) and high-altitude (5050m), II) Sherpa highlanders (n=8; 73 5050m), and III) Andean (with and without excessive erythrocytosis) highlanders (n=15; 74 4300m). Cardiovascular responses to MSNA burst sequences (i.e. singlet, couplet, triplet, and 75 quadruplets) were quantified using custom software (coded in MATLAB, v2015b). Slopes were 76 generated for each individual based on peak responses and normalized total MSNA. High 77 altitude reduced neuro-cardiovascular transduction in lowlanders (MAP slope: high-altitude, 78 0.0075±0.0060 vs low-altitude, 0.0134±0.080; p=0.03). Transduction was elevated in Sherpa 79 (MAP slope, 0.012±0.007) compared to Andeans (0.003±0.002; p=0.001). MAP transduction 80 was not statistically different between acclimatizing lowlanders and Sherpa (MAP slope, p=0.08) 81 or Andeans (MAP slope, p=0.07). When accounting for resting MSNA (ANCOVA), transduction 82 was inversely related to basal MSNA (bursts/min) independent of population (RRI, r= 0.578 83 p<0.001; MAP, r= -0.627 p<0.0001). Our results demonstrate transduction is blunted in 84 individuals with higher basal MSNA, suggesting blunted neuro-cardiovascular transduction is a 85 physiological adaptation to elevated MSNA rather than an effect or adaptation specific to 86 chronic hypoxic exposure.
American Journal of Physiology - Heart and Circulatory Physiology;
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., Figueroa-Mujíca, R., Vizcardo Galindo, G.A., Villafuerte, F.C., Gasho, C., Willie, C., Tymko, M., Ainslie, P., Stembridge, M., Moore, J.P. & Steinback, C.D. (2020) 'Highs and Lows of Sympathetic Neuro-cardiovascular Transduction: Influence of Altitude Acclimatization and Adaptation', American Journal of Physiology-Heart and Circulatory Physiology. https://doi.org/10.1152/ajpheart.00364.2020
Article published in AJP- Heart and Circulatory Physiology, available at https://doi.org/10.1152/ajpheart.00364.2020
Cardiff Metropolitan University (Grant ID: Cardiff Metropolian (Internal))
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