Venous Gas Bubbles: Production by Transient, Deep Isobaric Counterdiffusion of Helium Against Nitrogen

Abstract

When awake goats were subjected to isobaric gas switching from saturation (17 hours) on 4.7 atmospheres of nitrogen (0.3 atmosphere of oxygen) to 4.7 atmospheres of helium (0.3 atmosphere of oxygen), bubbles detected by 5-megahertz Doppler ultrasound in the posterior vena cava 20 to 60 minutes after the switch continued for 4 hours. Similar experiments carried out at 6.7 atmospheres of inert gas and 0.3 atmosphere of oxygen produced more bubbles for as long as 12 hours after the gas switch. This is believed to be the first objective demonstration of the phenomenon of deep isobaric supersaturation under transient operational diving conditions at relatively shallow diving depths. Detection of bubbles by Doppler ultrasound confirms the potential importance of the phenomenon to shallow saturation diving and holds promise for better quantitification of its effects as well as those of its counterpart, isobaric undersaturation, which can confer a decompression advantage.

Effect of isobaric breathing gas shifts from air to heliox mixtures on resolution of air bubbles in lipid and aqueous tissues of recompressed rats

“…This 2.6 times greater tissue–blood partition coefficient for N 2 relative to helium, causes adipose tissue to saturate (and desaturate) with helium more than twice as fast as with N 2 . Thus, upon an air to heliox breathing gas shift, a transient state of super saturation may be created, causing growth of N 2 bubbles (D’Aoust and Lambertsen 1982; D’Aoust et al 1977; Lambertsen and Idicula 1975). In aqueous tissues, this difference almost disappears, since the water/blood partition coefficient for N 2 is 0.966 as compared to 1.043 for helium.…”

“…Accordingly, if the rate of tissue saturation has any effect on bubble dynamics, one should expect this to be of importance in lipid as opposed to aqueous tissues, a fact corroborated by the results of the experiments presented here. D’Aoust BG and co-workers (1977) studied the continuous formation of intravascular gas bubble formation in goats, caused by an isobaric breathing gas shift from air to heliox breathing after a saturation exposure breathing 4.7 atmospheres (476 kPa) of nitrogen (0.3 atmosphere of oxygen). However, no adverse effects—or the development of DCS were reported in these animals.…”

“…In lipid tissues, the tissue–blood partition coefficient ratio for nitrogen is 2.6 times that of helium, which makes these tissues saturate (and desaturate) with helium more than twice as fast as with N 2 (Hyldegaard and Madsen 1989; Langø et al 1996; Weathersby and Homer 1980). Thus, a transient state of super-saturation may be created, that might cause growth of N 2 bubbles during breathing of a heliox mixture as suggested by Lambertsen and Idicula (1975) and D’Aoust et al (1977). …”

“…Super-saturation and formation of a gas phase induced by deep tissue isobaric counterdiffusion has been referred to in theoretical models and experimentally demonstrated by intravascular gas formation in animal models, when changing breathing gas from air to heliox (helium and oxygen mixture) in animals compressed to saturation on air (D’Aoust et al 1977; Lambertsen and Idicula 1975). Such a counterdiffusion phenomenon could in theory also cause growth of existing nitrogen-containing bubbles and thus deterioration of symptoms of air-diving-induced decompression sickness (DCS).…”

Decompression calculations for trimix dives with PC software: variations in the time-to-surface: where do they come from?

“…2.65); this factor is uniform to all compartments. This has been met with criticism from serious researchers in the fi eld (D'Aoust et al, 1979;Lightfoot et al, 1978;Rodchenkov and Skudin, 1992). Especially in newer experiments, the perfusion rates are viewed quite differently (Doolette, 2005).…”