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Hope this question hasn't been asked before. Apologies if it has.
I'm a little confused about how a patent foramen ovale (as opposed to atrial septal defect) can predispose to DCI.
I can see that a PFO would allow direct access of bubbles in the venous circulation to the arterial side, but given that left atrial pressures are higher than right atrial pressures, how can flow occur along an uphill pressure gradient and, in any case, would not the "flap valve" remain closed?
Or does right atrial pressure exceed left atrial pressure during left atrial diastole?
beche de mer once bubbled... Hope this question hasn't been asked before. Apologies if it has.
I'm a little confused about how a patent foramen ovale (as opposed to atrial septal defect) can predispose to DCI.
I can see that a PFO would allow direct access of bubbles in the venous circulation to the arterial side, but given that left atrial pressures are higher than right atrial pressures, how can flow occur along an uphill pressure gradient and, in any case, would not the "flap valve" remain closed?
Or does right atrial pressure exceed left atrial pressure during left atrial diastole?
Thanks.
During periods of exertion, or even a decent cough, the PFO can open and allow bubbles to pass thru the opening to the "wrong" side. The pressure reverses for a short period of time during the cough.
My cardiologist told me a sad story about a local weightlifter. He was in a competition, and collapsed. Seems that he had a PFO and when he exerted himself, some pieces of cholesterol (they believe) transferred to the wrong side. He's now in really bad shape.
When you take an ultrasound with a bubble study, you are asked to cough strongly when the bubbles are injected into your system. If you have a PFO, you can see the bubbles move to the other side.
I just went thru this, (and a TEE to confirm it). I'm glad I caught this before anything serious happened. Appointment later this month with the cardiac surgeon.
"I will spare you a gushy description of the dive itself, except to say that when you finally see what goes on underwater, you realize that you've been missing the whole point of the ocean. Staying on the surface all the time is like going to the circus and staring at the outside of the tent. "
-Dave Barry
I just went thru this, (and a TEE to confirm it). I'm glad I caught this before anything serious happened. Appointment later this month with the cardiac surgeon.
What's a TEE? Not wishing to pry, but how did you come to be having an ultrasound with bubbles? Was it a diving-related issue?
beche de mer once bubbled... Thanks DD. That sounds plausible.
What's a TEE? Not wishing to pry, but how did you come to be having an ultrasound with bubbles? Was it a diving-related issue?
TEE- Trans Esophogeal Echogram
Basically, they numb your throat and drop a long tube down it to get a much better picture of the heart from the inside. Thank goodness for sedation!
To make a long story short, my cousin had some serious heart problems, and it scared the crap out of all of us. I went in to see a cardiologist just as a precautionary measure. All my tests came out fine (thank goodness!), but in conversation with him I mentioned scuba diving. I knew about the PFO's from my readings, and he suggested that I do the ultrasound with bubble study. That came out with the PFO result and further tests were ordered.
"I will spare you a gushy description of the dive itself, except to say that when you finally see what goes on underwater, you realize that you've been missing the whole point of the ocean. Staying on the surface all the time is like going to the circus and staring at the outside of the tent. "
-Dave Barry
You will find lots of data about this on the Internet. One reason for bubbles to enter the arterial system is the change in pressure associated with the valsalva manouvre (pinch your nose and blow) which is used by most of us to equalise our ears.
The echocardiagram mentioned tests for PFO with this technique.
So - when you inadvertantly drop down the shot line a few feet at the end of a dive as other divers coming up pull the line down you instinctively equalise and shunt bubbles into the "wrong" part of the heart.
I have done this in the past - I guess many of us have. I have tried now to equalise using other methods as a precaution. PFO is present in about 30% of the population......
As yours is more a medical inquiry than one "concerning the scientific aspects of decompression," the focus of the Ask Dr Decompression forum, I have taken the liberty of moving it here.
A search of the board archives http://www.scubaboard.com/search.php reveals this info on PFO from last week. Scroll to the end of the last post of the thread:
DocVikingo once bubbled... As yours is more a medical inquiry than one "concerning the scientific aspects of decompression," the focus of the Ask Dr Decompression forum, I have taken the liberty of moving it here.
A search of the board archives http://www.scubaboard.com/search.php?s= reveals this info on PFO from last week. Scroll to the end of the last post of the thread:
A follow-up to the notes you wrote on the link posted:
It seems to me that if the fetus is allowing blood to pass thru this opening (which sounds like it is normal), then wouldn't diving while pregnant be contraindicated? Any bubble that the mother would generate would be passed directly thru the hole in the fetus's heart chamber and then to it's brain.
If this is the case, the suggestion that diving is acceptable to pregnant Mom's is way off base.
"I will spare you a gushy description of the dive itself, except to say that when you finally see what goes on underwater, you realize that you've been missing the whole point of the ocean. Staying on the surface all the time is like going to the circus and staring at the outside of the tent. "
-Dave Barry
Since the fetus does pass blood through the PFO and shunt it past the uninflected lungs, the unborn child would be at risk for DCS. The bubbles in question are generated in the baby’s tissues however, rather than the mother’s. The blood supplies are different. Diving while pregnant is a bad idea. This is not just my opinion but has laboratory data to back the position.
PFO and Atrial Septal Defect (ASD)
The PFO is a normal part of the growth and development process. It is necessary for the life of the baby in utero and generally closes within the first year. An ASD is a different thing. The can be all types of anomalies of development from the embryo to the full term infant.
One part that can be missing is either a portion of the atrial septum (wall) [ASD] or a portion of the ventricular septum [VSD].
Cross Over
While it is true that the pressure is higher in the left atrium than the right, this is not necessarily true throughout the breathing cycle. In some cases, in some individuals, at a certain point in the heart cycle and breathing cycle, the pressure in the right atrium can be higher than in the left. Arterialization is possible at this time. The migrating entity could be either a blood clot (and a possible vein-to-artery stroke) or gas bubbles in the case of divers.
Augmentation
It is also possible to increase the abnormal right-to-left gradient by certain actions. These involve holding your breath (holds blood back from entering the thorax and heart), and then releasing (causing a slug of blood to enter the right atrium). This is termed “rebound flow.” The actions promoting this are the Valsalva maneuver, straining with a breath hold, coughing, sneezing, pushing or lifting with a breath hold, and exerting yourself while climbing aboard a boat.
There is a higher incidence of neurological DCS than would be predicted from bends-only DCS. These actions in the field and not mimicked in the lab during table tests (for various reasons). Much of this is my own personal opinion and the view is not necessarily shared by other barophysiology specialists. These are all aspects of diving not built into dive algorithms and computers. :boom:
Michael R. Powell, M.S., Ph.D. "If a man empties his purse into his head, no man can take it away from him. An investment in Knowledge always pays the best Interest." - Benjamin Franklin
You indicate: "The PFO is a normal part of the growth and development process. It is necessary for the life of the baby in utero and generally closes within the first year. An ASD is a different thing."
It is my understanding that PFO legitimately can be, and in fact often is, considered a type of ASD.
A number of sources support this contention, but the following from the Mayo Clinic & eMedicine should suffice for the purposes of the present discussion--->
I call attention to the following remark under the section addressing "Ostium Secundum Atrial Septal Defect": "Ostium secundum ASD is the most common type of ASD. It occurs in the center of the septum between the right and left atrium. A variant of this type of ASD is called a patent foramen ovale (PFO) and is very small."
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