PFO and left to right shunting

[Red Sea Shadow]

We know right to left shunting might cause venous blood (containing inert gas bubbles) to bypass the lungs, where it should be filtered, and pass to the arterial side to be pumped around the body. We know also that bubbles can arterialize not only through PFO, but also through the pulmonary capillaries (so that's not what I'd be asking for).

Now what do you think would be the effect of left to right shunting on DCS? In other words, oxygen-rich blood from the arterial side passing through the foramen ovale to mix with the venous blood (containing bubbles); would that alter the risk of DCS?

 

[DocVikingo]

Hi RSS,

Left-to-right shunts can cause a diver to become short of breath, and feel weak and fatigued. They also can involve a number a potentially quite serious developments, such as damage to the pulmonary vasculature and irreversible pulmonary hypertension.

However, the implications of uncomplicated left-to-right shunts for DCS per se would be negligible.

Regards,

DocVikingo

 

[Red Sea Shadow]

Thanks DV.

 

[Dr Deco]

That would be my answer.

 

[TSandM]

An intracardiac left to right shunt diminishes the blood circulating to oxygenate the tissues, and increases the blood circulating through the lungs. The result can be a combination of inadequate forward flow to support any degree of increased demand, and pulmonary hypertension as the result of overcirculation. Both of these things will occur in the situation of large ventricular septal defects, for example.

However, the pressure differential between the atria is small and there is really no driving force to shunt blood from the left atrium to the right. On the other hand, Valsalva or other maneuvers that temporarily effect large increases in cardiac venous return can create small right to left pressure gradients, which is why we see bubbles passing from right to left on testing.