Chemoreflex mediated arrhythmia during apnea at 5,050 m in low-but not high-altitude natives
Van Diepen, S
Ainslie, Philip N.
American Physiological Society
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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 ± 6 yr) and Nepalese Sherpa (n = 8; age = 32 ± 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 ± 15 vs. 61 ± 15 beats/min; P < 0.01) that was similar to Sherpa (71 ± 5 beats/min; P = 0.94). High-altitude apnea caused arrhythmias in 11 of 14 Lowlanders [junctional rhythm (n = 4), 3° atrioventricular block (n = 3), sinus pause (n = 4)] not present at low altitude and larger marked bradycardia (nadir −39 ± 18 beats/min; P < 0.001). Sherpa exhibited a reduced bradycardia response during apnea compared with Lowlanders (P < 0.001) and did not develop arrhythmias. Hyperoxia blunted bradycardia (nadir −10 ± 14 beats/min; P < 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 < 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.
Journal of Applied Physiology;
Busch, S.A., Davies, H.E., Van Diepen, S., Simpson, L.L., Sobierajski, F., Riske, L., Stembridge, M., Ainslie, P.N., Willie, C.K., Hoiland, R.L. and Moore, J.P. (2017) 'Chemoreflex Mediated Arrhythmia during Apnea at 5050m in Low but not High Altitude Natives', Journal of Applied Physiology, 124(4), pp.930-937
Article published in Journal of Applied Physiology on 12 April 2018 - available at https://doi.org/10.1152/japplphysiol.00774.2017
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