Nitric Oxide and Oxidative Stress Changes at Depth in Breath-Hold Diving

Abstract

BackgroundSeveral 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 MethodsBlood 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.ResultsWe 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.DiscussionThe 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.

Endothelial Nitric Oxide Production and Antioxidant Response in Breath-Hold Diving: Genetic Predisposition or Environment Related?

“…Unlike the previous paper (decrease of TAC: −60% to predive value) (Cialoni et al, 2021), TAC did not show any difference between pre-and post-diving in the present experiment. This fact suggests the absence of an oxidative stimulus at the end of the training session, despite the hyperbaric exposure.…”

“…In a recent study, data obtained from an underwater blood draw (−42 m) carried out on 12 expert BH-divers clearly showed the NOx kinetics in BH-diving. These data indicate a significant underwater increase in plasma NOx concentration (+410.5% compared with pre-dive value) and an immediate return to baseline values after reaching the surface (Cialoni et al, 2021). These data confirmed a significant use of NO during BH-diving, compatible with the well-known BH-divingrelated circulatory adaptations, but unexpectedly showed a swift return of circulating NOx to basal levels at the surface.…”

“…Hyperbaric exposure-related oxidative stress is the second aspect taken into account due to the consequences potentially affecting BH-divers. Indeed, BH-diving results in higher ROS production and oxidative stress, as confirmed by several authors (Theunissen et al, 2013a;Mrakic-Sposta et al, 2019;Cialoni et al, 2021), along with the activation of endogenous antioxidant defenses (Bulmer et al, 2008;Sureda et al, 2015). As recently suggested (Cialoni et al, 2021), oxidative stress is transitory, increasing in the underwater phases but returning near pre-dive levels after reaching the surface.…”

“…Therefore, the T30 post-diving reduction of NO x found in this experiment can be ascribed to the lower NO availability in the first few minutes after the dives caused by the higher use of this molecule during diving (Cialoni et al, 2021) to ensure the BH-diving related vascular adaptations. On the other hand, an increase at T60 could be a rebound of the efforts of the body to restore basal conditions after exceptional stress exposure (Figure 1).…”

High-Throughput Griess Assay of Nitrite and Nitrate in Plasma and Red Blood Cells for Human Physiology Studies under Extreme Conditions

“…NO plays a key role in subjects exposed to high hydrostatic pressures (i.e., the one of water during diving) [ 4 ], and recent measurements taken in SCUBA divers and breath-hold divers at −40 m depth showed remarkable increases in the plasma concentrations of NO derivatives [ 5 , 6 ]. Breathing air at hyperbaric conditions raises oxygen partial pressure (pO 2 ), leading to hyperoxia and causing vasoconstriction and oxidative stress [ 7 , 8 ], which is at the base of endothelial dysfunction.…”