The Magnitude of Diving Bradycardia During Apnea at Low-Altitude Reveals Tolerance to High Altitude Hypoxia.

Pontus Holmström,Prakash Limbu,Eric Mulder,Angelica Lodin Sundström,Erika Schagatay

doi:10.3389/fphys.2019.01075

Abstract

Acute mountain sickness (AMS) is a potentially life-threatening illness that may develop during exposure to hypoxia at high altitude (HA). Susceptibility to AMS is highly individual, and the ability to predict it is limited. Apneic diving also induces hypoxia, and we aimed to investigate whether protective physiological responses, i.e., the cardiovascular diving response and spleen contraction, induced during apnea at low-altitude could predict individual susceptibility to AMS. Eighteen participants (eight females) performed three static apneas in air, the first at a fixed limit of 60 s (A1) and two of maximal duration (A2–A3), spaced by 2 min, while SaO2, heart rate (HR) and spleen volume were measured continuously. Tests were conducted in Kathmandu (1470 m) before a 14 day trek to mount Everest Base Camp (5360 m). During the trek, participants reported AMS symptoms daily using the Lake Louise Questionnaire (LLQ). The apnea-induced HR-reduction (diving bradycardia) was negatively correlated with the accumulated LLQ score in A1 (rs = −0.628, p = 0.005) and A3 (rs = −0.488, p = 0.040) and positively correlated with SaO2 at 4410 m (A1: r = 0.655, p = 0.003; A2: r = 0.471, p = 0.049; A3: r = 0.635, p = 0.005). Baseline spleen volume correlated negatively with LLQ score (rs = −0.479, p = 0.044), but no correlation was found between apnea-induced spleen volume reduction with LLQ score (rs = 0.350, p = 0.155). The association between the diving bradycardia and spleen size with AMS symptoms suggests links between physiological responses to HA and apnea. Measuring individual responses to apnea at sea-level could provide means to predict AMS susceptibility prior to ascent.

Highlights

Recreational trekking has become a popular sporting activity, and approximately 40 million people travel to high altitude (HA; ≥3000 m) each year (Neupane and Swenson, 2017)
The principal findings were that: (I) the apnea-induced associated with SaO2 at high altitude (HA); (III) resting bradycardia for at m (A1) and A3 was negatively associated with spleen volume was negatively associated with accumulated Lake Louise Questionnaire (LLQ) accumulated LLQ score; (II) the apnea-induced bradycardia was score with ascent
We found that the group with least Acute mountain sickness (AMS) symptoms, had both larger resting spleen volume and maximal spleen volume reduction compared to the group who developed most AMS symptoms, indicating the superior contractile function of the bigger spleens, allowing a greater increase in red blood cells (RBCs), which is associated with tolerance to HA hypoxia

Summary

Introduction

Recreational trekking has become a popular sporting activity, and approximately 40 million people travel to high altitude (HA; ≥3000 m) each year (Neupane and Swenson, 2017). As both the individual rate of acclimatization (Schoene et al, 1984; Gallagher and Hackett, 2004) as well as the individual susceptibility to acute mountain sickness (AMS) varies greatly (Oliver et al, 2012), the prediction of individual susceptibility is imperative to reduce AMS incidence. At 3500 and 4300 m both resting SaO2 and post-exercise SaO2 were lower in participants who developed AMS at higher altitudes. Some researchers have failed to find any association between AMS and SaO2 at altitude (Wagner et al, 2012)

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