Orientation during deco/safety stop

[DrSteve]

It seems to me that why people latch onto DIR is due to the rigors of the training and the fact that DIR divers can back up everything they do with a reason. Plus it's not a case of pay your money and get the card as it is with other agencies (I bet though if you explained to the non-DIR-F certified guys what Hogarthian was, they would relate to that as well). You have to work for it. I am the same way with BSAC (at least the pre-1994 system), rigorous training both in the class room, pool and open water. For many this shows that DIR-F is more difficult to get and thus superior to PADI, SSI, NAUI, YMCA et al. Just my thoughts.

 

[lamont]

In a drysuit with a dramatic loss of buoyancy (i.g. runaway inflator), last resort is to be head-up vertical, dumping gas from your suit and/or wing, and disconnecting hose(s). . .

I can actually kick down against a fully-inflated wing and maintain position. I think I'd rather be head down, kicking down, dumping out the rear dump. Although I know of one unsuccessful attempt to do that and one successful attempt to just dump gas out of the corrugated hose and disconnect the LP hose.

 

[Dr Deco]

Hello catherine96821:

This position appears to have fallen by the wayside. It was originally developed
for the case of a considerable infusion of air into the vascular system [vena cava] and filling the right ventricle; after its originator, it was called the “Durant position.” It certainly was of value, at least in dogs. This position reduced the problem of an "air lock" in the heart where one could hear a “waterwheel murmur” with a stethoscope. This position would be of value in some cases of surgical accidents, but humans seldom have such bubble loads in the normal course of diving.

The thought was also to keep the free gas bubbles away from the outflow tract and prevent their entrance into the arterial system. With few bubbles, the churning of the blood in the heart probably reduced this idea to wishful thinking.

It does not appear that it is successful for gas bubbles in the aorta either; a reference appears below. This examines the movement of bubbles after they reach the arterial system, and it is not the same as movement of bubbles within the right ventricle

Dr Deco :doctor:

The next class in Decompression Physiology for 2006 is September 16 – 17. :1book: http://wrigley.usc.edu/hyperbaric/advdeco.htm


References :book3:

Butler BD, Laine GA, Leiman BC, Warters D, Kurusz M, Sutton T, Katz J. Effect of the Trendelenburg position on the distribution of arterial air emboli in dogs. Ann Thorac Surg. 1988 Feb;45(2):198-202.

Department of Anesthesiology, University of Texas Medical School, Houston 77030.

We examined the effects of buoyancy on the distribution of arterial gas bubbles using in vitro and in vivo techniques in dogs. A simulated carotid artery preparation was used to determine the effects of bubble size and vessel angle on the velocity and direction of bubble movement in flowing blood. Because buoyancy tends to float bubbles away from dependent areas, bubble velocity would be expected to decrease as the vessel angle increased. We found that larger bubbles increased in velocity in the same direction as the blood flow at 0-, 10-, and 30-degree vessel angles and decreased when the vessel was positioned at 90 degrees. Smaller bubbles did not change velocity from zero to 30 degrees and increased in velocity in the same direction as blood flow at 90 degrees. In 10 anesthetized dogs, we studied the effects of 0-, 10-, 15-, and 30-degree Trendelenburg's position on carotid artery distribution of gas bubbles injected into the left ventricle or ascending aorta. Regardless of the degree of the Trendelenburg position, the bubbles passed into the carotid artery simultaneously with passage into the abdominal aorta. We conclude that the forces of buoyancy do not overcome the force of arterial blood flow and that the Trendelenburg position does not prevent arterial bubbles from reaching the brain.

 

[DrSteve]

The next class in Decompression Physiology for 2006 is September 16 – 17. :1book: http://wrigley.usc.edu/hyperbaric/advdeco.htm

I'd love to do that course, but no way I can get to Catalina for it. Have you considered running it as a web course? Or perhaps videoing it and selling it?

 

[jbd]

Hello Dr Steve:

There is such a degree of safety built into decompression tables and meters that something such as body position would not make a difference in decompression incidence.

You can rest assured vertical or horizontal will produce the same result.

Dr Deco :doctor:

The next class in Decompression Physiology for 2006 is September 16 – 17. :1book: http://wrigley.usc.edu/hyperbaric/advdeco.htm

It amazes me that the good Dr. Deco makes this point twice in this thread and seemingly no one gets it, rather there is continued discussion of cross sectioning the vascular beds of the lungs in varying body attitudes in the water column. From a physiological point it makes no difference whether one is supine, prone, head done vertical, head up vertical, horizontal on the left side or the right side during the stop.
Re-read the good Dr's comments and follow his recommendations and quit over thinking the simple concept of making and holding a stop.

 

[Kevrumbo]

It amazes me that the good Dr. Deco makes this point twice in this thread and seemingly no one gets it, rather there is continued discussion of cross sectioning the vascular beds of the lungs in varying body attitudes in the water column. From a physiological point it makes no difference whether one is supine, prone, head done vertical, head up vertical, horizontal on the left side or the right side during the stop.
Re-read the good Dr's comments and follow his recommendations and quit over thinking the simple concept of making and holding a stop.

Nope; this is not something to be glibly dismissed, especially in light of accidents that've been happening lately. Every little advantage that you can get to ensure a clean Deco is wise and should be utilized --especially in non-military, non-commercial, "Sport" Technical Deep Mixed Gas Diving. Maybe Dr. Deco can get funding to examine & test this concept of off-gassing efficiency: vertical vs. horizontal positioning (some experimental paradigm involving a specialized Lung Perfusion Scan on a diver in a large deep water tank). . .

 

[jbd]

I suspect he already knows or understands what the efficiency differences are . I believe the point is that there is not a significant enough difference to make a difference. Making and holding the stop at the specified depth for the specified makes a huge difference compared to no stop or too short of a stop. Light activity during the stop apparently makes a notable difference as well. Body orientation for offgassing efficiency is micro-analyzing the issue to the point of absurdity.

Horizontal body orientation is more pertinent to the comments made by lamont.

I doubt that the accidents you mention had anything to do with body orientation during a stop. More likely there were larger issues involved.

 

[LavaSurfer]

YPeople may seek out a Mercedes dealership while they run from the Jehovah's Witness at their front door

:lol::lol:

 

[Saturation]

For diving position between vertical or horizontal [ also called prone for diving, meaning face down in the water] there are a number of studies regarding work and breathing efficiency. Its summarized in Bennett & Elliott's ... Diving Medicine.

In a nutshell, some studies show it is easier to breathe in the prone position, and in some studies no differences were found. For heavy work, position shows no difference, but its far easier to work in the vertical position. Navy and commercial divers do not use fins work vertically, often with weighted shoes.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=Abstract&list_uids=11820330&query_hl=1&itool=pubmed_docsum

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=Abstract&list_uids=1561722&query_hl=1&itool=pubmed_docsum

In over 1000+ dives I've done, I find it hardest to breathe in the upright or vertical position the shallower you are and supine, that is face up in the water. These findings are all supported by many studies on OC scuba, it has to do with compression of lung volume and the cracking pressure of the regulator.

Usually past 30' and far deeper, the only advantage true prone position has is in swimming efficiency especially against a current, it provides the smallest surface area to current.

I have witness several accidents, with no major consequences, by the rigid teaching of this prone position, often to new divers. The prone position is not optimal to obtain leverage to remove stuck hoses quickly especially in cold water and gloved hands; gas bubbles in a wing are only maximally position for venting when the vent port is vertical ... best on top of the wing towards the inflator hose. In there is a runaway power inflator, the vertical position allows venting even before the wing fills. In many wings, the bottom segments are slightly wider and are not joined into a continuous loop, so venting the rear port exhausts only half the wing. A leaking LP hose can be snapped off in 1-2 seconds, versus the number of turns needed to shut a valve on the offending post.

 

[Cacia]

Hello catherine96821:

This position appears to have fallen by the wayside. It was originally developed
for the case of a considerable infusion of air into the vascular system [vena cava] and filling the right ventricle; after its originator, it was called the “Durant position.” It certainly was of value, at least in dogs. This position reduced the problem of an "air lock" in the heart where one could hear a “waterwheel murmur” with a stethoscope. This position would be of value in some cases of surgical accidents, but humans seldom have such bubble loads in the normal course of diving.

The thought was also to keep the free gas bubbles away from the outflow tract and prevent their entrance into the arterial system. With few bubbles, the churning of the blood in the heart probably reduced this idea to wishful thinking.


QUOTE]

Thanks for that..very interesting.