{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,4]],"date-time":"2026-07-04T18:25:06Z","timestamp":1783189506092,"version":"3.54.6"},"reference-count":36,"publisher":"American Physiological Society","issue":"4","funder":[{"DOI":"10.13039\/501100002790","name":"Canadian Network for Research and Innovation in Machining Technology, Natural Sciences and Engineering Research Council of Canada","doi-asserted-by":"crossref","award":["RGPIN-2014-06637"],"award-info":[{"award-number":["RGPIN-2014-06637"]}],"id":[{"id":"10.13039\/501100002790","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100002790","name":"Canadian Network for Research and Innovation in Machining Technology, Natural Sciences and Engineering Research Council of Canada","doi-asserted-by":"crossref","award":["20150821-01"],"award-info":[{"award-number":["20150821-01"]}],"id":[{"id":"10.13039\/501100002790","id-type":"DOI","asserted-by":"crossref"}]},{"name":"Presidents Grant for Creative and Performance Arts - Human Performance Fund","award":["HPF-162"],"award-info":[{"award-number":["HPF-162"]}]},{"name":"Canadian Research Chair in Cerebrovascular Physiology","award":["950-230970"],"award-info":[{"award-number":["950-230970"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Journal of Applied Physiology"],"published-print":{"date-parts":[[2018,4,1]]},"abstract":"<jats:p> Peripheral chemoreflex mediated increases in both parasympathetic and sympathetic drive under chronic hypoxia may evoke bradyarrhythmias during apneic periods. We determined whether 1) voluntary apnea unmasks arrhythmia at low (344 m) and high (5,050 m) altitude, 2) high-altitude natives (Nepalese Sherpa) exhibit similar cardiovagal responses at altitude, and 3) bradyarrhythmias at altitude are partially chemoreflex mediated. Participants were grouped as Lowlanders ( n = 14; age = 27 \u00b1 6 yr) and Nepalese Sherpa ( n = 8; age = 32 \u00b1 11 yr). Lowlanders were assessed at 344 and 5,050 m, whereas Sherpa were assessed at 5,050 m. Heart rate (HR) and rhythm (lead II ECG) were recorded during rest and voluntary end-expiratory apnea. Peripheral chemoreflex contributions were assessed in Lowlanders ( n = 7) at altitude after 100% oxygen. Lowlanders had higher resting HR at altitude (70 \u00b1 15 vs. 61 \u00b1 15 beats\/min; P &lt; 0.01) that was similar to Sherpa (71 \u00b1 5 beats\/min; P = 0.94). High-altitude apnea caused arrhythmias in 11 of 14 Lowlanders [junctional rhythm ( n = 4), 3\u00b0 atrioventricular block ( n = 3), sinus pause ( n = 4)] not present at low altitude and larger marked bradycardia (nadir \u221239 \u00b1 18 beats\/min; P &lt; 0.001). Sherpa exhibited a reduced bradycardia response during apnea compared with Lowlanders ( P &lt; 0.001) and did not develop arrhythmias. Hyperoxia blunted bradycardia (nadir \u221210 \u00b1 14 beats\/min; P &lt; 0.001 compared with hypoxic state) and reduced arrhythmia incidence (3 of 7 Lowlanders). Degree of bradycardia was significantly related to hypoxic ventilatory response (HVR) at altitude and predictive of arrhythmias ( P &lt; 0.05). Our data demonstrate apnea-induced bradyarrhythmias in Lowlanders at altitude but not in Sherpa (potentially through cardioprotective phenotypes). The chemoreflex is an important mechanism in genesis of bradyarrhythmias, and the HVR may be predictive for identifying individual susceptibility to events at altitude. <\/jats:p><jats:p> NEW &amp; NOTEWORTHY The peripheral chemoreflex increases both parasympathetic and sympathetic drive under chronic hypoxia. We found that this evoked bradyarrhythmias when combined with apneic periods in Lowlanders at altitude, which become relieved through supplemental oxygen. In contrast, high-altitude residents (Nepalese Sherpa) do not exhibit bradyarrhythmias during apnea at altitude through potential cardioprotective adaptations. The degree of bradycardia and bradyarrhythmias was related to the hypoxic ventilatory response, demonstrating that the chemoreflex plays an important role in these findings. <\/jats:p>","DOI":"10.1152\/japplphysiol.00774.2017","type":"journal-article","created":{"date-parts":[[2017,12,25]],"date-time":"2017-12-25T02:40:39Z","timestamp":1514169639000},"page":"930-937","source":"Crossref","is-referenced-by-count":26,"title":["Chemoreflex mediated arrhythmia during apnea at 5,050 m in low- but not high-altitude natives"],"prefix":"10.1152","volume":"124","author":[{"given":"Stephen A.","family":"Busch","sequence":"first","affiliation":[{"name":"Neurovascular Health Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hannah","family":"Davies","sequence":"additional","affiliation":[{"name":"Neurovascular Health Laboratory, Faculty of Physical Education and Recreation, 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