Nitric Oxide And Oxidative Stress Changes At Depth in Breath-Hold Diving
Authors: Danilo Cialoni, Andrea Brizzolari, Michele Samaja, Gerardo Bosco, Matteo Paganini, Massimo Pieri, Valentina Lancellotti and Alessandro Marroni
DOI / Source: https://doi.org/10.3389/fphys.2020.609642
Date: 07 January 2021
Reading level: Intermediate
Why This Matters for Freedivers
Deep dives can trigger short, intense internal shifts that disappear quickly at the surface, so “post-dive normal” doesn’t always mean “nothing happened.” Just because it's not easy to observe changes, that doesn't mean damage hasn't been done to cells that requires adequate recovery. It supports being conservative with pacing and recovery, especially when doing repeated deep dives.
Synopsis
When you freedive, your body rapidly adjusts blood flow to protect vital organs. A key chemical involved is nitric oxide (NO), which helps blood vessels relax and can improve circulation. But deep dives also change oxygen pressure and stress the body, which can briefly increase oxidative stress (reactive molecules your body has to neutralize).
In this study, 14 experienced freedivers dove in the Y-40 pool to −42 m, and researchers took blood samples before, at the bottom, right after surfacing, and 30–60 minutes later. At depth, divers showed a strong rise in NO “footprints” (NOx increased roughly fourfold) and a big drop in the blood’s antioxidant “buffer” (TAC fell by about 60%). The striking part is how fast this reversed: as soon as they surfaced, both values returned to normal and stayed normal afterward. Another marker linked to fat/lipid damage (TBARS) did not change, suggesting no clear sign of that type of damage from this protocol. The main message is that important physiological changes may happen only at depth and can be missed if you measure only after the dive.
Abstract
Background: Several mechanisms allow humans to resist the extreme conditions encountered during breath-hold diving. Available nitric oxide (NO) is one of the major contributors to such complex adaptations at depth and oxidative stress is one of the major collateral effects of diving. Due to technical difficulties, these biomarkers have not so far been studied in vivo while at depth. The aim of this study is to investigate nitrate and nitrite (NOx) concentration, total antioxidant capacity (TAC) and lipid peroxidation (TBARS) before, during, and after repetitive breath-hold dives in healthy volunteers.
Materials and Methods: Blood plasma, obtained from 14 expert breath-hold divers, was tested for differences in NOx, TAC, and TBARS between pre-dive, bottom, surface, 30 and 60 min post-dive samples.
Results: We observed a statistically significant increase of NOx plasma concentration in the “bottom blood draw” as compared to the pre-dive condition while we did not find any difference in the following samples We found a statistically significant decrease in TAC at the bottom but the value returned to normality immediately after reaching the surface. We did not find any statistically significant difference in TBARS.
Discussion: The increased plasma NOx values found at the bottom were not observed at surface and post dive sampling (T0, T30, T60), showing a very rapid return to the pre-dive values. Also TAC values returned to pre- diving levels immediately after the end of hyperbaric exposure, probably as a consequence of the activation of endogenous antioxidant defenses. TBARS did not show any difference during the protocol.