Effect of a short-acting NO donor on bubble formation from a saturation dive in pigs

Abstract

It has previously been reported that a nitric oxide (NO) donor reduces bubble formation from an air dive and that blocking NO production increases bubble formation. The present study was initiated to see whether a short-acting NO donor (glycerol trinitrate, 5 mg/ml; Nycomed Pharma) given immediately before start of decompression would affect the amount of vascular bubbles during and after decompression from a saturation dive in pigs. A total of 14 pigs (Sus scrofa domestica of the strain Norsk landsvin) were randomly divided into an experimental (n = 7) and a control group (n = 7). The pigs were anesthetized with ketamine and alpha-chloralose and compressed in a hyperbaric chamber to 500 kPa (40 m of seawater) in 2 min, and they had 3-h bottom time while breathing nitrox (35 kPa O(2)). The pigs were all decompressed to the surface (100 kPa) at a rate of 200 kPa/h. During decompression, the inspired Po(2) of the breathing gas was kept at 100 kPa. Thirty minutes before decompression, the experimental group received a short-acting NO donor intravenously, while the control group were given equal amounts of saline. The average number of bubbles seen during the observation period decreased from 0.2 to 0.02 bubbles/cm(2) (P < 0.0001) in the experimental group compared with the controls. The present study gives further support to the role of NO in preventing vascular bubble formation after decompression.

Intramicroparticle nitrogen dioxide is a bubble nucleation site leading to decompression-induced neutrophil activation and vascular injury

“…Infusinġ NO donor drugs reduces injury in decompressed animals and decreases the number of intravascular bubbles in both animals and humans (6,23,34,39). Given the varied effects of˙NO these findings are not necessarily contradictory to observations in our study.…”

Could beaked whales get the bends?

“…Yet it is only under unusual circumstances that DCS symptoms are observed, suggesting the possibility that they may have additional specialized adaptations to reduce DCS risk during their normal diving routine. Research has shown a potential link between bubbles and nitric oxide levels in terrestrial mammals (Wisloff et al, 2004;Mollerlokken et al, 2006). It has been suggested that nitric oxide alters the endothelial interface and reduces bubble nuclei, thereby preventing formation of bubbles.…”

Effect of nitric oxide on spinal evoked potentials and survival rate in rats with decompression sickness

“…It has been suggested that NO induces alterations in the hydrophobicity of the endothelial wall, which reduces the stability and density of the nuclei precursors adhering to the surface (8, 28, 38, 39), causing less gas to evolve as bubbles. Furthermore, it has also been suggested that NO, through augmented blood flow, may increase the N 2 washout and thereby promote bubble shrinkage (28); however, as discussed by Moon (29) and Wisloff et al (39), GTN has a very short half-time, and, since reduced flow during decompression appears of minor importance, the first hypothesis seems more attractive (29,39).…”

“…The most widely accepted theory suggests that NO induces alterations in the hydrophobicity of the endothelial wall, which reduces the stability and density of the micronuclei precursors adhering to the surface (8,28,38,39). It has also been suggested that NO enhances the blood flow rate and thereby promotes bubble shrinkage through an increased N 2 washout from tissues (28).…”

“…In experimental settings, the nitric oxide (NO) releasing agents, glycerol trinitrate [nitroglycerine (GNT)] and isosorbide-5-mononitrate (ISMN), have been shown to significantly reduce intravascular bubble formation and to increase the survival rate during DCS from diving (8,28,38); however, the exact mechanism by which NO prevents DCS has not been clarified. The most widely accepted theory suggests that NO induces alterations in the hydrophobicity of the endothelial wall, which reduces the stability and density of the micronuclei precursors adhering to the surface (8,28,38,39).…”