Hyperbaric hyperoxia induces a neuromuscular hyperexcitability: assessment of a reduced response in elite oxygen divers

Abstract

We compared the changes in compound muscle mass action potential (M-wave) recorded in vastus lateralis in response to hyperbaric hyperoxia (HBO) in nine combat divers who dived daily while breathing 100% O2 or O2-enriched mixture (O2 divers) to those measured in eight recreational divers who dived occasionally using compressed air/21% O2 (air divers). The O2 divers completed a 6-h HBO exposure in which the inspired oxygen pressure (PiO2) varied from 1.15 to 2.7 absolute atmospheres (ATA), PiO2 being maintained at 1.15 ATA throughout the first 2-h period, whereas the air divers only completed a 2-h HBO exposure with PiO2 constant at 1.15 ATA. Before HBO exposure, there were no intergroup differences between baseline M-wave characteristics (amplitude and duration), but the conduction time was significantly shorter in O2 divers compared with air divers. After 90 min of HBO (1.15 ATA) the air divers demonstrated neuromuscular hyperexcitability, as evidenced by an increased M-wave amplitude (13%, P<0.01 versus baseline), shortened M-wave duration (5%, P<0.05 versus baseline), and reduced conduction time (5%, P<0.01 versus baseline). In O2 divers, similar HBO-induced M-wave changes were only observed when PiO2 was greater than 1.50 ATA. We conclude that HBO elicites neuromuscular hyperexcitability, attenuated in elite O2 divers.

Effect of hyperoxic and hyperbaric conditions on the adenosinergic pathway and CD26 expression in rat

“…In this respect, it is worthwhile to note here that 1) the hyperoxic conditions achieved in our experiments mimic conditions that are used in human, inasmuch as 1-bar O 2 is a common treatment of CO poisoning and 2-bar O 2 is used notably by combat divers (31), suggesting that the effects we observed here can be found in humans; 2) the way hyperoxia regulates the adenosine response, as shown here, contributes to explain how and why hyperoxia promotes vasoconstriction (24); 3) our data are consistent with the observation that a low oxygen level induces adenosine release and high A 2A R expression, in particular in peripheral blood mononuclear cells (13,22,35,56,63).…”

“…Hyperbaric conditions, notably hyperbaric oxygenation, have established medical, mountaineering, and diving applications because of their capacity to increase the oxygen level in tissues, 1-atmosphere oxygen being used for example in the treatment of carbon monoxide poisoning and 2-atmosphere oxygen being used as breathing gas by divers in extreme conditions (31,62). Although it displays major side effects such as production of reactive oxygen species (3), the use of hyperoxygenation is strongly growing.…”

Hyperoxia enhances metaboreflex sensitivity during static exercise in humans

“…Another explanation could be that hyperoxia elicits neuromuscular hyperexcitability (20). Greater MSNA and MBP responses were observed not only during hyperoxic exercise but also during PE-CA in hyperoxia, when metaboreceptors are activated in the absence of other reflex mechanisms.…”

“…Finally, there is evidence in animal studies that hyperoxia markedly increases the activation of sensory endings in skeletal muscle and enhances the discharge of group IV muscle afferents (4,20). However, in healthy young subjects, short periods of hyperoxia did not affect sympathetic activation to rhythmic exercise (38).…”

“…However, in skeletal muscle with hyperoxia, this may not prevail over activation of sensory endings (4,20) because BL is only one of numerous mediators of the metaboreflex response (40). We decided, therefore, to test the hypothesis that prolonged hyperoxia enhances the MSNA and BP responses to isometric exercise even in the presence of reduced BL production.…”