Introduction: Study of physiological adaptation in people breathing rarefied air in a cave.

Objective: To investigate the arrhythmogenic capacity of rarefied air and changes the autonomic nervous system (sympathetic and parasympathetic). To establish cutoff levels beyond which preventive measures must be taken.

Method: The study included 25 cavers, monitored by ECG Holter and blood pressure measurements in 2 situations at rest, one outside the cave breathing normal air composition (NA), and the other underground, breathing rarefied air of natural origin (RA) in a confined space (O2: 13.38 ± 1.5% and CO2: 2.23 ± 0.31%).

Results: Resting heart rate (NA: 81.9 ± 15.1 beats per minute (bpm) vs. RA: 83.8 ± 17.3 bpm; P ≤ .58). Systolic blood pressure (NA: 130.3 ± 17.2 mmHg vs. RA: 140.2 ± 21.3 mmHg; P ≤ .0003). Diastolic blood pressure (NA: 78.2 ± 11.0 mmHg vs. RA: 85.5 ± 11.2 mmHg; P ≤ .0002). Heart rate variability: RMSSD (NA: 25.9 ± 13.8 ms vs. RA: 36.9 ± 17.8 ms; P ≤ .003), NN50 (NA: 49.0 ± 66.2 bpm vs. RA: 111.7 ± 102.8 bpm; P ≤ .003); pNN50 (NA: 11.3% ± 7.5 vs. RA: 15.9 ± 15.8%; P ≤ .0013). Fourier analysis: TP (NA: 1,759.5 ms2 vs. RA: 2,611.5 ms2; P ≤ .04); HF (NA: 301.5 ± 329.4 ms2 vs. RA: 662.3 ± 762.8 ms2; P ≤ .02). An increase in arrhythmic events is detected when comparing the hour that included test 1 (HNA) in normal air with the hour that included test 2 (HRA) with rarefied air. There is a correlation of arrhythmic events in both situations: (ventricular ectopic beats in RA) = 2.9859 × (ventricular ectopic beats NA) + 1.5622; n = 24; r = 0.814; P <.0001.

Conclusions: Exposure to RA at rest for 10 minutes causes a pressor response in systolic and diastolic blood pressure compared to normal air (NA). Heart rate variability in a standardised situation and rest shows a parasympathetic response, with increased rMSSD and HF parameters when subjects are subjected to an atmosphere of RA. In RA, the subjects had three times more arrhythmic events when compared to NA.

© 2016 Consell Català de l’Esport. Generalitat de Catalunya. Published by Elsevier España, S.L.U. All rights reserved.