Duration at high altitude influences the onset of arrhythmogenesis during apnea

Berthelsen, Lindsey F.; Diepen, Sean van; Steele, Andrew R.; Berg, Emily R. Vanden; Bird, Jordan; Thrall, Scott; Skalk, Alexandra; Byman, Britta; Pentz, Brandon; Wilson, Richard J. A.; Jendzjowsky, Nicholas G.; Day, Trevor A.; Steinback, Craig D.

doi:10.1007/s00421-021-04842-x

Cited by 3 publications

(1 citation statement)

References 44 publications

(66 reference statements)

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“…Our study is in agreement with previous work from our group assessing SSCD with ascent (Berthelsen et al, 2022 ; Bird, Kalker, et al, 2021 ; Bird, Leacy, et al, 2021 ; Bruce et al, 2018 ; Leacy et al, 2021 ). In the present study, we clearly demonstrate that SSCD captures VA with incremental ascent to 4240 m over 7 days in a large group of lowlanders.…”

Section: Discussionsupporting

confidence: 93%

Steady‐state chemoreflex drive captures ventilatory acclimatization during incremental ascent to high altitude: Effect of acetazolamide

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Bruce

Marullo

et al. 2022

Physiological Reports

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Ventilatory acclimatization (VA) is important to maintain adequate oxygenation with ascent to high altitude (HA). Transient hypoxic ventilatory response tests lack feasibility and fail to capture the integrated steady‐state responses to chronic hypoxic exposure in HA fieldwork. We recently characterized a novel index of steady‐state respiratory chemoreflex drive (SSCD), accounting for integrated contributions from central and peripheral respiratory chemoreceptors during steady‐state breathing at prevailing chemostimuli. Acetazolamide is often utilized during ascent for prevention or treatment of altitude‐related illnesses, eliciting metabolic acidosis and stimulating respiratory chemoreceptors. To determine if SSCD reflects VA during ascent to HA, we characterized SSCD in 25 lowlanders during incremental ascent to 4240 m over 7 days. We subsequently compared two separate subgroups: no acetazolamide (NAz; n = 14) and those taking an oral prophylactic dose of acetazolamide (Az; 125 mg BID; n = 11). At 1130/1400 m (day zero) and 4240 m (day seven), steady‐state measurements of resting ventilation (V̇ I ; L/min), pressure of end‐tidal (P ET )CO 2 (Torr), and peripheral oxygen saturation (SpO 2 ; %) were measured. A stimulus index (SI; P ET CO 2 /SpO 2 ) was calculated, and SSCD was calculated by indexing V̇ I against SI. We found that (a) both V̇ I and SSCD increased with ascent to 4240 m (day seven; V̇ I : +39%, p < 0.0001, Hedges' g = 1.52; SSCD: +56.%, p < 0.0001, Hedges' g = 1.65), (b) and these responses were larger in the Az versus NAz subgroup (V̇ I : p = 0.02, Hedges' g = 1.04; SSCD: p = 0.02, Hedges' g = 1.05). The SSCD metric may have utility in assessing VA during prolonged stays at altitude, providing a feasible alternative to transient chemoreflex tests.

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Section: Discussionsupporting

confidence: 93%

Steady‐state chemoreflex drive captures ventilatory acclimatization during incremental ascent to high altitude: Effect of acetazolamide

Cates

Bruce

Marullo

et al. 2022

Physiological Reports

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The influence of training status and parasympathetic blockade on the cardiac rate, rhythm, and functional response to autonomic stress

Berthelsen

Douglas

Dawkins

et al. 2023

Appl. Physiol. Nutr. Metab.

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Apnea (breath-holding) elicits co-activation of sympathetic and parasympathetic nervous systems, affecting cardiac control. In situations of autonomic co-activation (e.g., cold water immersion), cardiac arrhythmias are observed during apnea. Chronic endurance training reduces resting heart rate in part via elevation in parasympathetic tone, and has been identified as a risk factor for development of arrhythmias. However, few studies have investigated autonomic control of the heart in trained athletes during stress. Therefore, we determined whether heightened vagal tone resulting from endurance training promotes a higher incidence of arrhythmia during apnea. We assessed the heart rate, rhythm (ECG lead II), and cardiac inotropic (speckle-tracking echocardiography) response to apnea in 10 endurance trained and 7 untrained participants. Participants performed an apnea at rest and following sympathetic activation using post-exercise circulatory occlusion (PECO). All apneas were performed prior to (CON) and following vagal block using glycopyrrolate (GLY). Trained participants had lower heart rates at rest (p=0.03) and during apneas (p=0.009) under CON. At rest, 3 trained participants exhibited instances of junctional rhythm and 4 trained participants developed ectopy during CON apneas, whereas 3 untrained participants developed ectopic beats only with concurrent sympathetic activation (PECO). Following GLY, no arrhythmias were noted in either group. Vagal block also revealed increased cardiac chronotropy (heart rate) and inotropy (strain rate) during apnea, demonstrating a greater sympathetic influence in the absence of parasympathetic drive. Our results highlight that endurance athletes may be more susceptible to ectopy via elevated vagal tone, whereas untrained participants may only develop ectopy through autonomic conflict.

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Case Studies in Physiology: Is blackout in breath-hold diving related to cardiac arrhythmias?

Mulder

Längle

Pernett

et al. 2023

Journal of Applied Physiology

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Syncope or "blackout" (BO) in breath-hold diving (freediving) is generally considered to be caused by hypoxia. However, it has been suggested that cardiac arrhythmias affecting the pumping effectivity could contribute to BO. BO is fairly common in competitive freediving, where athletes aim for maximal performance. We recorded heart rate (HR) during a static apnea (STA) competition, to reveal if arrhythmias occur. Four male freedivers with STA personal best (PB) of 349±43s, volunteered during national championships, where they performed STA floating face down in a shallow indoor pool. A non-coded Polar T31 chest strap recorded R-R intervals and a water- and pressure proof pulse oximeter arterial oxygen saturation. Three divers produced STA near their PB without problems, while one diver ended with BO at 5min17s, which was 12s beyond his PB. He was immediately brought up by safety divers and resumed breathing within 10s. All divers attained similar lowest diving HR (47±4bpm), but HR recordings displayed a different pattern for the diver ending with BO. After a short tachycardia the three successful divers developed bradycardia which became more pronounced during the second half of the apnea. The fourth diver developed pronounced bradycardia earlier, and at 2.5min into the apnea HR started alternating between approximately 50 and 140 bpm, until the diver lost consciousness. At resumed breathing, HR returned to baseline. Nadir oxygen saturation was similar for all divers. We speculate that arrhythmia could have contributed to BO, by lowering stroke volume leading to a systolic blood pressure drop, affecting brain perfusion.

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Duration at high altitude influences the onset of arrhythmogenesis during apnea

Cited by 3 publications

References 44 publications

Steady‐state chemoreflex drive captures ventilatory acclimatization during incremental ascent to high altitude: Effect of acetazolamide

Steady‐state chemoreflex drive captures ventilatory acclimatization during incremental ascent to high altitude: Effect of acetazolamide

The influence of training status and parasympathetic blockade on the cardiac rate, rhythm, and functional response to autonomic stress

Case Studies in Physiology: Is blackout in breath-hold diving related to cardiac arrhythmias?

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