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  • 1.
    Bakker, Emily
    et al.
    Norwegian Univ Sci & Technol, Dept Circulat & Med Imaging, Fac Med, KG Jebsen Ctr Exercise Med, N-7006 Trondheim, Norway..
    Engan, Harald
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. ;LHL Hlth, LHL Klinikkene Raros, Roros, Norway..
    Patrician, Alexander
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Karlsen, Trine
    Norwegian Univ Sci & Technol, Dept Circulat & Med Imaging, Fac Med, KG Jebsen Ctr Exercise Med, N-7006 Trondheim, Norway.;St Olavs Univ Hosp, Trondheim, Norway..
    Wisloff, Ulrik
    Norwegian Univ Sci & Technol, Dept Circulat & Med Imaging, Fac Med, KG Jebsen Ctr Exercise Med, N-7006 Trondheim, Norway..
    Gaustad, Svein Erik
    Norwegian Univ Sci & Technol, Dept Circulat & Med Imaging, Fac Med, KG Jebsen Ctr Exercise Med, N-7006 Trondheim, Norway..
    Acute dietary nitrate supplementation improves arterial endothelial function at high altitude: A double-blinded randomized controlled cross over study2015In: Nitric oxide, ISSN 1089-8603, E-ISSN 1089-8611, Vol. 50, p. 58-64Article in journal (Refereed)
    Abstract [en]

    Introduction: Dietary nitrate (NO3-) supplementation serves as an exogenous source of nitrite (NO3-) and nitric oxide (NO) through the NO3- NO3- NO pathway, and may improve vascular functions during normoxia. The effects of NO3- supplementation in healthy lowlanders during hypobaric hypoxia are unknown. Purpose: Determine the effect of acute oral NO3- supplementation via beetroot juice (BJ) on endothelial function (flow mediated dilation; FMD) in lowlanders at 3700 m. Methods: FMD was measured using ultrasound and Doppler in the brachial artery of 11 healthy subjects (4 females, age 25 +/- 5 yrs; height 1.8 +/- 0.1 m, weight 72 +/- 10 kg) sojourning to high altitude. In a randomized, double-blinded crossover study design, FMD was measured 3 h after drinking BJ (5.0 mmol NO3-) and placebo (PL; 0.003 mmol No-3(-)) supplementation at 3700 m, with a 24-h wash out period between tests. FMD was also measured without any BJ supplementation pre-trek at 1370 m, after 5 days at 4200 m and upon return to 1370 m after 4 weeks of altitude exposure (above 2500 m). The altitude exposure was interrupted by a decent to lower altitude where subjects spent two nights at 1370 m before returning to altitude again. Results: Ten subjects completed the NO3- supplementation. FMD (mean +/- SD) pre-trek value was 6.53 +/- 2.32% at 1370 m. At 3700 m FMD was reduced to 3.84 +/- 1.31% (p < 0.01) after PL supplementation but was normalized after receiving BJ (5.77 +/- 1.14% (p = 1.00). Eight of the subjects completed the interrupted 4-week altitude stay, and their FMD was lower at 4200 m (FMD 3.04 +/- 2.22%) and at post-altitude exposure to 1370 m (FMD 3.91 +/- 2.58%) compared to pre-trek FMD at 1370 m. Conclusion: Acute dietary NO3- supplementation may abolish altitude-induced reduction in endothelial function, and can serve as a dietary strategy to ensure peripheral vascular function in lowland subjects entering high altitude environments. (C) 2015 Elsevier Inc. All rights reserved.

  • 2.
    Bakker, Emily
    et al.
    Norwegian Univ Sci & Technol, N-7034 Trondheim, Norway.
    Engan, Harald
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Patrician, Alexander
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Karlsen, Trine
    Norwegian Univ Sci & Technol, N-7034 Trondheim, Norway.
    Wisloff, Ulrik
    Norwegian Univ Sci & Technol, N-7034 Trondheim, Norway.
    Gaustad, Svein Erik
    Norwegian Univ Sci & Technol, N-7034 Trondheim, Norway.
    Effects Of Dietary Nitrate Supplementation On Endothelial Function At High Altitude2014In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 46, no 5, p. 424-424Article in journal (Other academic)
  • 3.
    Engan, Harald
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Bakker, Emily
    Norwegian Univ Sci & Technol, Trondheim, Norway..
    Patrician, Alexander
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Gaustad, SE
    Norwegian Univ Sci & Technol, Trondheim, Norway..
    Karlsen, T
    Norwegian Univ Sci & Technol, Trondheim, Norway..
    Wisløff, U
    Norwegian Univ Sci & Technol, Trondheim, Norway..
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Reductions in endothelial function during altitude exposure2014Conference paper (Refereed)
  • 4.
    Engan, Harald
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Mattiason, S
    Norwegian Univ Sci & Technol, Trondheim, Norway..
    Bakker, Emily
    Norwegian Univ Sci & Technol, Trondheim, Norway..
    Patrician, Alexander
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Effect of dietary nitrate supplementation on blood pressure in native lowlanders at altitude2014Conference paper (Refereed)
  • 5. Fernández, FA
    et al.
    Patrician, Alexander
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Lodin-Sundström, Angelica
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Predicting static and dynamic apnea performance in elite divers using a 2-minute static apnea test2015Conference paper (Refereed)
  • 6.
    Johansson, Hampus
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Engan, Harald K.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Melin, Maja
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Patrician, Alexander
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Lodin-Sundström, Angelica
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    No effect of dietary nitrate on the human diving response in dry and wet apneas2015Conference paper (Refereed)
  • 7.
    Johansson, O
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Patrician, Alexander
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Wisniewski, Sarah
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Spirometry during ascent to altitude and its correlation to acute mountain sickness2014Conference paper (Refereed)
    Abstract [en]

    Easily measurable variables capable of predicting altitude sickness, before symptom onset, would be beneficial for those requiring slower ascent or even medical attention. Unfortunately few such reliable factors exist. Our objective was to test respiratory function during ascent in the Nepali Himalaya, to see if any correlations with altitude sickness, expressed by Lake Louis scores, could be identified. Eleven healthy subjects (six male and five female, mean(SD) age 26(9.3) years) travelled from 1370m to 4200m, and spent 9 days at or above this altitude. Variables of lung function, including vital capacity, forced expiratory volume over one second (FEV1) and peak expiratory flow were measured using a portable spirometer every-other morning before breakfast in the standing position. Subjects also completed the Lake Louis self-assessment questionnaire daily. Mean(SD) vital capacity and FEV1 decreased from 5.3(1.4) L and 4.5(0.9) L at 1370m to 4.8(1.4) L and 4.2(1.0) L at 4200m, respectively (p<0.05), but did not correlate to Lake Louis scores. Mean(SD) peak expiratory flow was 9.4(2.3) L/s at 1370m and did not change during ascent. However once at 4200m it increased from 9.2(2.7) L/s to 9.6(2.4) L/s following the stay at altitude (p<0.05). Interestingly, an absolute change in peak expiratory flow at 4200m compared to 1370m, showed a high correlation to Lake Louis scores at 3700m and 4200m (r= -0.971; p<0.001). We conclude that peak expiratory flow values were closely related to signs of altitude sickness, and should be explored further for determining their predictive value.

  • 8.
    Melin, Maja
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Lodin-Sundström, Angelica
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Johansson, Hampus
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Patrician, Alexander
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Engan, Harald K.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    The effect of dietary nitrate on spleen contraction and Hb increase during apnea2015Conference paper (Refereed)
  • 9.
    Patrician, Alexander
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Engan, Harald K.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Norwegian Heart & Lung Patient Org, LHL Klinikkene Roros, Oslo, Norway.
    Lundsten, David
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Grote, Ludger
    Sahlgrens Univ Hosp, Sleep Disorders Ctr, Pulm Med, Gothenburg.
    Vigetun-Haughey, Helena
    Capio St Gorans Hosp, Dept Clin Physiol, Stockholm.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    The Effect of Dietary Nitrate on Nocturnal Sleep-Disordered Breathing and Arterial Oxygen Desaturation at High Altitude2018In: High Altitude Medicine & Biology, ISSN 1527-0297, E-ISSN 1557-8682, Vol. 19, no 1, p. 21-27Article in journal (Refereed)
    Abstract [en]

    Patrician, Alexander, Harald Engan, David Lundsten, Ludger Grote, Helena Vigetun-Haughey, and Erika Schagatay. The effect of dietary nitrate on nocturnal sleep-disordered breathing and arterial oxygen desaturation at high altitude. High Alt Med Biol 00:000-000, 2017.Sleep-disordered breathing and fluctuations in arterial oxygen saturation (SaO(2)) are common during sleep among lowlanders ascending to high altitude. Dietary nitrate (NO3-) supplementation has been shown to lower the O-2 consumption in various conditions. Our objective was to investigate whether dietary NO3- could reduce sleep-disordered breathing and SaO(2) desaturation during sleep at altitude. Cardiorespiratory responses during sleep were measured in 10 healthy lowlanders at 330m and then again in the Himalayas at 3700-4900m. Each subject received two 70mL shots of either beetroot juice (BR; approximate to 5.0mmol NO3- per shot) or placebo (PL: approximate to 0.003mmol NO3- per shot) in a single-blinded, weighted order over two consecutive nights at altitude. At 2.5-4.5 hours into sleep at altitude, BR increased the SaO(2) desaturation drop (4.2 [0.1]% with PL vs. 5.3 [0.4]% with BR; p=0.024) and decreased the SaO(2) desaturation duration (14.1 [0.9] seconds with PL to 11.1 [0.9] seconds with BR; p=0.0.041). There was a reduction in breaths with flow limitation (p=0.025), but no changes in Apnea-Hypopnea Index (AHI), mean and minimum SaO(2). The study suggests BR supplementation does not improve AHI or oxygenation, but may increase fluctuations in arterial O-2 saturation during sleep at altitude in native lowlanders.

  • 10.
    Patrician, Alexander
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Engan, Harald
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Lundsten, David
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Effects of Dietary Nitrate on Sleep at Altitude2014Conference paper (Refereed)
  • 11.
    Patrician, Alexander
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Johansson, Hampus
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Melin, Maja
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Lodin-Sundström, Angelica
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Engan, Harald K.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    The effect of dietary nitrate on spleen contraction and diving response during apnea2015Conference paper (Refereed)
  • 12.
    Patrician, Alexander
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Dietary nitrate enhances arterial oxygen saturation after dynamic apnea2017In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 27, no 6, p. 622-626Article in journal (Refereed)
    Abstract [en]

    Breath-hold divers train to minimize their oxygen consumption to improve their apneic performance. Dietary nitrate has been shown to reduce the oxygen cost in a variety of situations, and our aim was to study its effect on arterial oxygen saturation (SaO2) after dynamic apnea (DYN) performance. Fourteen healthy male apnea divers (aged 33 ± 11 years) received either 70 mL of concentrated nitrate-rich beetroot juice (BR) or placebo (PL) on different days. At 2.5 h after ingesting the juice, they were asked to perform 2 × 75 m DYN dives in a pool with 4.5-min recovery between dives. Each dive started after 2-min countdown and without any warm-up apneas, hyperventilation, or lung packing. SaO2 and heart rate were measured via pulse oximetry for 90 s before and after each dive. Mean SaO2 nadir values after the dives were 83.4 ± 10.8% with BR and 78.3 ± 11.0% with PL (P &lt; 0.05). At 20-s post-dive, mean SaO2 was 86.3 ± 10.6% with BR and 79.4 ± 10.2% with PL (P &lt; 0.05). In conclusion, BR juice was found to elevate SaO2 after 75-m DYN. These results suggest an oxygen conserving effect of dietary nitrate supplementation, which likely has a positive effect on maximal apnea performance.

  • 13.
    Patrician, Alexander
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Dietary nitrate reduces oxygen cost for dynamic apnea2014Conference paper (Refereed)
  • 14.
    Rodríguez-Zamora, Lara
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Lodin-Sundström, Angelica
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Engan, Harald K.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Höök, Martina
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Patrician, Alexander
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Degerström, E
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Effects of altitude acclimatization on spleen volume and contraction during submaximal and maximal work in lowlanders2015Conference paper (Refereed)
  • 15.
    Rodríguez-Zamora, Lara
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Patrician, Alexander
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Starfelt, Victor
    Olander, Carl
    Lodin-Sundström, Angelica
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Schagatay, Erika
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Physiological responses to apnea at sea level predict SaO2 at simulated 5300 m altitude2016Conference paper (Refereed)
  • 16.
    Schagatay, Erika
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Patrician, Alexander
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Engan, Harald
    LHL Klinikkene Roros, Roros, Norway.
    Lodin-Sundström, Angelica
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Spleen Contraction and Hb Increase after Nitrate Ingestion may Explain Enhanced Apneic Diving Performance2017In: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 219, no S710, p. 32-32, article id P-42Article in journal (Refereed)
    Abstract [en]

    INTRODUCTION: Ingesting nitrate-rich beetroot juice (BJ) has been suggested to enhance physical performance by reducing the oxygen cost, which could be useful in apneic diving. We previously found that after ingestion of BJ, arterial oxygen saturation was higher after static apneas (Engan et.al, Resp. Physiol & Neurobiol, 2012) and after dynamic apneas involving exercise (Patrician & Schagatay. Scand.J.Med.Sci.Sports, 2016). Our aim was to investigate the effect of BJ ingestion on spleen contraction and the resulting Hb increase, a mechanism known to prolong apneas (Schagatay et.al, J.Appl.Physiol, 2001).

    MATERIALS AND METHODS: Eight volunteers aged 24±2 years simulated diving by performing maximal apneas with face immersion during prone rest ~2.5h after ingesting 70 ml BJ (5 mmol NO3-) or placebo (0.003 mmol NO3-) on separate days in a weighted order. We measured spleen diameters for volume calculation and capillary Hb before and after "dives".

    RESULTS: Baseline (mean±SE) spleen volume was 269±33 mL with placebo and 206±27 mL after BJ ingestion (P<0.05). Post "dive" spleen volumes were smaller, but similar at 168±35 mL and 193±25 mL, respectively (NS). Baseline Hb was 145.4±3.4 g/L with placebo and 149.8±2.6 g/L with BJ (P<0.05). Post "dive" Hb had increased to 152.0±4.8 g/L with placebo and 153.7±3.0 g/L with BJ (NS). 

    CONCLUSION: With BJ ingestion spleen volume was reduced and Hb elevated even before the "dive". The elevated Hb at the start of apnea would likely have a positive effect on apneic duration by enhancing circulating oxygen stores. The positive effect of nitrate on performance in various sports could in part be due to its spleen-emptying effect, causing a natural blood boosting, which is a novel finding.

  • 17.
    Sjöström, Rita
    et al.
    Umeå Universitet; Östersund sjukhus.
    Söderström, Lars
    Östersunds sjukhus.
    Klockmo, Carolina
    Kommunförbundet Västernorrland.
    Patrician, Alexander
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Sandström, Thomas
    Umeå Universitet.
    Björklund, Glenn
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Hanstock, Helen
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Stenfors, Nikolai
    Umeå Universitet.
    Qualitative identification and characterisation of self-reported symptoms arising in humans during experimental exposure to cold air2019In: International Journal of Circumpolar Health, ISSN 2242-3982, E-ISSN 2242-3982, Vol. 78, no 1, article id 1583528Article in journal (Refereed)
    Abstract [en]

    Background: Exposure to cold air is associated with increased morbidity and mortality in the general population. It is difficult to study the effects of whole-body exposure to cold air under controlled conditions in real life. Objectives: The aim of this study was to (1) explore and describe the experience of symptoms in humans during experimental and controlled exposures to cold air, by using controlled environmental chamber exposures and qualitative methodology, and to (2) categorise the symptoms. Method: The study used a randomised, double blind design, in which 34 subjects undertook rest and moderate-intensity exercise in an environmental chamber set to two or three different temperatures (0, −10, and −17°C) on separate occasions. During the chamber exposures, subjects were interviewed. Qualitative content analysis was selected as the method of analysis. Findings: Subjects reported 50 distinct symptoms during the exposures. The symptoms were grouped into ten sub-categories and two major categories; airway versus whole-body symptoms. Conclusion: We have identified a broad range of symptoms in humans undertaking rest and moderate-intensity exercise at sub-zero temperatures. The symptoms and their categories may well be used to more extensively and quantitatively map cold-induced morbidity.

  • 18.
    Tymko, Michael M.
    et al.
    Univ British Columbia, Sch Hlth & Exercise Sci, Ctr Heart Lung & Vasc Hlth, Kelowna, BC, Canada.
    Tremblay, Joshua C.
    Queens Univ, Sch Kinesiol & Hlth Studies, Cardiovasc Stress Response Lab, Kingston, ON, Canada.
    Steinback, Craig D.
    Univ Alberta, Fac Phys Educ & Recreat, Edmonton, AB, Canada.
    Moore, Jonathan P.
    Bangor Univ, Extremes Res Grp, Sch Sport Hlth & Exercise Sci, Bangor, Gwynedd, Wales.
    Hansen, Alex B.
    Univ British Columbia, Sch Hlth & Exercise Sci, Ctr Heart Lung & Vasc Hlth, Kelowna, BC, Canada.
    Patrician, Alexander
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Howe, Connor A.
    Univ British Columbia, Sch Hlth & Exercise Sci, Ctr Heart Lung & Vasc Hlth, Kelowna, BC, Canada.
    Hoiland, Ryan L.
    Univ British Columbia, Sch Hlth & Exercise Sci, Ctr Heart Lung & Vasc Hlth, Kelowna, BC, Canada.
    Green, Daniel J.
    Univ Western Australia, Sch Sports Sci Exercise & Hlth, Crawley, WA, Australia; Liverpool John Moores Univ, Res Inst Sport & Exercise Sci, Liverpool, Merseyside, England.
    Ainslie, Philip N.
    Univ British Columbia, Sch Hlth & Exercise Sci, Ctr Heart Lung & Vasc Hlth, Kelowna, BC, Canada.
    UBC-Nepal Expedition: acute alterations in sympathetic nervous activity do not influence brachial artery endothelial function at sea level and high altitude2017In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 123, no 5, p. 1386-1396Article in journal (Refereed)
    Abstract [en]

    Evidence indicates that increases in sympathetic nervous activity (SNA), and acclimatization to high altitude (HA), may reduce endothelial function as assessed by brachial artery flow-mediated dilatation (FMD); however, it is unclear whether such changes in FMD are due to direct vascular constraint, or consequential altered hemodynamics (e.g., shear stress) associated with increased SNA as a consequence of exposure to HA. We hypothesized that 1) at rest, SNA would be elevated and FMD would be reduced at HA compared with sea-level (SL);and 2) at SL and HA, FMD would be reduced when SNA was acutely increased, and elevated when SNA was acutely decreased. Using a novel, randomized experimental design, brachial artery FMD was assessed at SL (344 m) and HA (5,050 m) in 14 participants during mild lower-body negative pressure (LBNP; -10 mmHg) and lower-body positive pressure (LBPP; -10 mmHg). Blood pressure (finger photoplethysmography), heart rate (electrocardiogram), oxygen saturation (pulse oximetry), and brachial artery blood flow and shear rate (Duplex ultrasound) were recorded during LBNP, control, and LBPP trials. Muscle SNA was recorded (via microneurography) in a subset of participants (n = 5). Our findings were 1) at rest, SNA was elevated (P < 0.01), and absolute FMD was reduced (P = 0.024), but relative FMD remained unaltered (P = 0.061), at HA compared with SL; and 2) despite significantly altering SNA with LBNP (+60.3 +/- 25.5%) and LBPP (-37.2 +/- 12.7%) (P < 0.01), FMD was unaltered at SL (P = 0.448) and HA (P = 0.537). These data indicate that acute and mild changes in SNA do not directly influence brachial artery FMD at SL or HA.

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