Cardiovascular pressures with venous gas embolism and decompression

Area of Science:

• Physiology
• Cardiovascular Science
• Diving and Aviation Medicine

Background:

• Venous gas embolism (VGE) occurs during decompression, potentially leading to neurological symptoms if bubbles cross into the arterial system.
• A patent foramen ovale (PFO) is present in 25-34% of the population, yet not all individuals with VGE experience neurological decompression illness.
• The pressure gradient across the heart's atria is hypothesized to be a protective mechanism against bubble arterialization.

Purpose of the Study:

• To investigate the effect of venous gas embolism (VGE), hyperbaric, and hypobaric decompression on the interatrial pressure gradient in dogs.
• To determine if pressure gradient reversals occur that would allow for bubble passage from venous to arterial circulation.

Main Methods:

• Anesthetized dogs (n=22) underwent VGE induction (0.025-0.15 ml.kg-1.min-1 for 180 min) or hyperbaric/hypobaric decompression.
• Left ventricular end-diastolic pressure was measured to estimate left atrial pressure.
• The pressure gradient across the atrial septum was continuously monitored.

Main Results:

• No sustained reversals of the mean pressure gradient across the atria were observed in 92 experimental evaluations.
• Only three transient reversals occurred during peak pressure changes.
• These findings suggest the normal pressure gradient is usually maintained during decompression stress.

Conclusions:

• The typical pressure gradient across the atria likely prevents significant arterialization of venous gas emboli.
• This mechanism may explain why neurological decompression illness is not more prevalent in individuals with patent foramen ovale and VGE.
• Further research may elucidate the precise conditions under which pressure gradients can be overcome.