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

Abstract

Deep tissue isobaric counterdiffusion that may cause unwanted bubble formation or transient bubble growth has been referred to in theoretical models and demonstrated by intravascular gas formation in animals, when changing inert breathing gas from nitrogen to helium after hyperbaric air breathing. We visually followed the in vivo resolution of extravascular air bubbles injected at 101 kPa into nitrogen supersaturated rat tissues: adipose, spinal white matter, skeletal muscle or tail tendon. Bubbles were observed during isobaric breathing-gas shifts from air to normoxic (80:20) heliox mixture while at 285 kPa or following immediate recompression to either 285 or 405 kPa, breathing 80:20 and 50:50 heliox mixtures. During the isobaric shifts, some bubbles in adipose tissue grew marginally for 10–30 min, subsequently they shrank and disappeared at a rate similar to or faster than during air breathing. No such bubble growth was observed in spinal white matter, skeletal muscle or tendon. In spinal white matter, an immediate breathing gas shift after the hyperbaric air exposure from air to both (80:20) and (50:50) heliox, coincident with recompression to either 285 or 405 kPa, caused consistent shrinkage of all air bubbles, until they disappeared from view. Deep tissue isobaric counterdiffusion may cause some air bubbles to grow transiently in adipose tissue. The effect is marginal and of no clinical consequence. Bubble disappearance rate is faster with heliox breathing mixtures as compared to air. We see no reason for reservations in the use of heliox breathing during treatment of air-diving-induced decompression sickness.

Mechanical ventilation and resuscitation under water: Exploring one of the last undiscovered environments – A pilot study

“…However, the general risk of decompression sickness due to isobaric counterdiffusion appears to be low. 20 Nevertheless, HeliOx gas mixtures are expensive, and less costly approaches like a further modification of the Oxylator ® to permit higher gas flows during the inspiratory cycle are more promising. A depth-dependent increase in the flow rates inside the Oxylator ® would probably be the best solution.…”

Comparison of treatment recompression tables for neurologic decompression illness in swine model

“…The counter-diffusion phenomenon has been proposed as another mechanism for potentially detrimental effects of heliox recompression treatment by causing growth of nitrogen-containing bubbles. Experimental studies have yielded heterogeneous results [22][23][24].…”

“…22), heart rate (p = 0.48), respiratory rate (p = 0.53), or pulse oxygen saturation (p = 0.99).Qualitative comparison of the spinal cord histological samples identified the thoracic region of the spinal cord, roughly corresponding to slidesnumbers 7-12 (Fig 6A), as the most severely damaged (Fig 6B). Representative samples are shown in Fig 7.…”