Abstract
Impaired flow mediated dilation (FMD), an index of vascular stress, is known after SCUBA diving. This is related to a dysfunction of nitric oxide (NO) availability and a disturbance of the redox status, possibly induced by hyperoxic/hyperbaric gas breathing. SCUBA diving is usually performed with a mask only covering “half face” (HF) and therefore forcing oral breathing. Nasal NO production is involved in vascular homeostasis and, as consequence, can significantly reduce NO possibly promoting vascular dysfunction. More recently, the utilization of “full-face” (FF) mask, allowing nasal breathing, became more frequent, but no reports are available describing their effects on vascular functions in comparison with HF masks. In this study we assessed and compared the effects of a standard shallow dive (20 min at 10 m) wearing either FF or a HF mask on different markers of vascular function (FMD), oxidative stress (ROS, 8-iso-PGF2α) and NO availability and metabolism (NO2, NOx and 3-NT and iNOS expression). Data from a dive breathing a hypoxic (16% O2 at depth) gas mixture with HF mask are shown allowing hyperoxic/hypoxic exposure. Our data suggest that nasal breathing might significantly reduce the occurrence of vascular dysfunction possibly due to better maintenance of NO production and bioavailability, resulting in a better ability to counter reactive oxygen and nitrogen species. Besides the obvious outcomes in terms of SCUBA diving safety, our data permit a better understanding of the effects of oxygen concentrations, either in normal conditions or as a strategy to induce selected responses in health and disease.
Highlights
Recreational SCUBA diving is considered a safe leisure activity
The utilization of full-face masks during SCUBA diving allows breathing through the nose, which is a confirmed physiological strategy to increase circulating nitric oxide (NO) [8], potentially modulating the effects of diving on flow mediated dilation (FMD)
In the present study, targeting the effect of nasal breathing on NO production as related to oxidative stress due to increased oxygen partial pressure, we focused our attention on the inducible form, but we did not exclude that eNOS activity could be affected by a temporary alteration of intracellular Ca availability from the endoplasmic reticulum [50]. inducible nitric oxide synthase (iNOS) expression after a dive performed while breathing a hypoxic air mixture and wearing a mask that only allows mouth breathing can be due to the activation of NF-κB transcription factor, as confirmed by several publications [51]
Summary
Recreational SCUBA (self-contained underwater breathing apparatus) diving is considered a safe leisure activity. It is known to induce (generally mild) adaptive responses potentially interfering with different physiological pathways, some of them being possibly harmful. When SCUBA divers stay at depth, they are exposed to inert gas supersaturation that may be translated into vascular gas emboli (VGE) during and following ascent while decompressing [1]. Decompression-induced bubble formation is a pivotal event in decompression sickness (DCS), the exact pathophysiological mechanisms.
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