Patent Foramen Ovale
By Brad Starks 2002-11-26
As you can see from the above illustrations, blood normally travels from the body into the right atrium (Venous circulation), then into the right ventricle and to the lungs. From the lungs blood travels to the left atrium and into left ventricle and lastly to the rest of the body. In a normal individual, If a bubble were to form in the venous circulation (i.e. air embolism) it would travel back to the right atrium and into the right ventricle and to the lungs. If the bubble is too large to pass through the pulmonary capillary bed then it would become lodged there and cause a pulmonary air embolism. If it was small enough to pass through the pulmonary capillary bed it would next travel to the left atrium, into the left ventricle, and into the systemic circulation. If the atmospheric pressure continued to decrease the bubble would enlarge and become lodged somewhere en route. It may be in the systemic circulation or it may be in the venous circulation. Where the bubble will lodge is purely dependent on its size and the size of the vessel it is passing through.
In the case of a PFO, the process is similar. In this case, however, if the bubble formed in the venous circulation and was small enough to continue to the right atrium, it MAY pass into the left atrium and bypass the lungs thereby entering the systemic circulation. If the atmospheric pressure continued to decrease, while the bubble was in the systemic circulation, then the bubble would enlarge and become lodged. If it continued to be small, it would then travel back to the right atrium where again it MAY pass into the left atrium or it may go to the lungs. The point is....in either a normal individual or an individual with a PFO, the bubble will lodge somewhere and cause blood flow to cease thus causing hypoxia.....then anoxia...and finally cell death.
The possibility of a bubble traveling from the right atrium into the left atrium ( in the case of PFO) is increased only when there is an increase in the right atrial pressure ( as in the case of pulmonary artery atresia, stenosis, or an obstructive lung disease. Normally, even with a PFO, the right atrium has an equal or lower pressure then the left atrium so if anything blood will be forced into the right atrium from the left.
As you can see, PFO's do not increase the risk of an air embolism. It may have an effect on where the bubble lodges, but the result is the same. I hope this clears up any confusion. If anyone disagrees with my synopsis, please feel free to refer me to a research article that states the contrary. I am always interested in learning new ideas. Thank you!
Brad Starks MSII