Blood Pressure and Inert Gas Loading

[Blackwood]

This question is directed at Dr. D, but any opinions are welcome.

It is commonly held that high blood pressure contributes to DCI in divers. My understanding is that since the hemodynamic pressure is higher than average, it pushes the inert gas out of solution faster than average (per Henry).

My question: is the opposite also true?

Some background: The last two times my fiancée dove she got DCS. Each were two dive days. Each had extremely benign profiles. The most recent occurrence: two 50-minute dives to 50 feet max (<30 feet average) with a 60 minute SI. First dive on EAN32, second dive on EAN36.

She didn’t notice any DCS symptoms until about 36 hours after the second dive.

She’s been tested for predisposing conditions such as PFO, and all tests were negative (of course, the PFO test is prone to false negatives, so who knows?).

How did she get loaded enough during the aforementioned dive profiles to get a Type II DCS hit?

Recently, her doctor noted that she has low blood pressure. It got me thinking. If high blood pressure pushes inert gasses out quickly, it follows that low blood pressure would accept inert gasses quickly. So someone with lower blood pressure than mine will absorb more nitrogen than I will on exactly the same dive profile. Further, said person will retain the nitrogen longer.

Right? Wrong? Any comments?

 

[Blackwood]

Shoot... I meant to put this in the Ask Dr. Deco forum...

 

[Wildcard]

Was this confirmed DCS? With that profile, it's hard to believe. Any other predisposing factors? Im still grinding the low BP thing around in my head so I don't have an answer for that. Just how low is it?

 

[Blackwood]

Was this confirmed DCS? With that profile, it's hard to believe. Any other predisposing factors? Im still grinding the low BP thing around in my head so I don't have an answer for that. Just how low is it?

It was diagnosed and treated by a hyperbaric MD. She rode the chamber and it went away at "depth" (60'). So either it was DCS, or it was a huge coincidence or an annoying little trick of the mind.

I'm not sure. It's not always low, either.

 

[Wildcard]

Wow! I hope Dr D can help you out, that a pretty scary thing to get bent that easy. Sorry, I don't have an answer. I suspect some metabolic issue but that way out of my field.

 

[knotical]

It is commonly held that high blood pressure contributes to DCI in divers.

I was not aware of this. Could you perhaps point us to a reference?

 

[Blackwood]

I was not aware of this. Could you perhaps point us to a reference?

I would swear that I've read that in multiple diving manuals, but I could very easily be wrong.

Regardless, your post got me thinking some more, and I think I may have at least one faulty assumption (beyond "high PB leads to DCS").

To my understanding, if you introduce a soluble gas (such as nitrogen) to a tissue (such as blood), the gas will dissolve into the blood if there is a pressure gradient.

At the surface (when we are completely off-gased), our blood is saturated (will not accept any more nitrogen) because the pressure in our blood = the pressure of the gas we are breathing. Similarly, once your tissues become saturated at depth, you won't on-gas any more without increasing depth.

I think a faulty assumption on my part may have been using overall blood pressure as part of the aforementioned gradient. Rather, I should have considered PN2internal vs. PN2external, and I don't believe that high blood pressure -> higher PN2 of the blood.

 

[wedivebc]

Not a doctor but don't see how that could be true. The blood is the conduit that transfers gas to and from the tissue but the pressure in the tissue (where DCS affects) is still controlled by ambient pressure and not the pressure acting on the walls of the blood vessels.

 

[fisherdvm]

Low blood pressure as a reading from a pressure cuff can be very misleading. Direct arterial pressure is accurate, but is too invasive for daily use. A blood pressure cuff has a range of sizes it would fit. If your arm is in the small range, it would over estimate your pressure, and if your arm is in the large range, it would underestimate the pressure.

I think the risk of DCS from hypertension is not due to the bloodpressure itself. But is due to the changes in the small arteries in the spine, and brain. Chronic hypertension leads to changes in these small vessels - making them smaller and more likely to occlude from nitrogen. At least that is my vague understanding why hypertensive patients are more likely to have peripheral vascular diseases of their small digits and skin. In the same way, the process likely occurs in the spinal cord and brain - leading to higher risk of DCS. This is only a theory.

In order to prove this theory - one would have to do enough autopsies on dead DCS victims with hypertension - if my theory is correct - wall changes in the small arteries might be found and might be related to hypertension.

My gut feeling is - hypotension is not a risk for DCS.

 

[Gene_Hobbs]

Wow, I had to dig way back to see anything on this one. The only thing I have found so far is:

Variations of the Pulse Rate and Arterial Blood Pressure under Increased Barometric Pressure and Their Prognostic Value in the Occurrence of Compressed Air Illness. Van Der Aue et. al. 1945

http://archive.rubicon-foundation.org/
Rubicon Repository ID: 123456789/3314
NEDU-1945-02, AD0758949

Im still grinding the low BP thing around in my head so I don't have an answer for that.

I second this... Gut thoughts are no real difference due to ALL of the other physiology involved. It is really hard to say anything about just BP alone.