Effects on Pressure on the Body

[DiveGolfSki]

As part of emergency training, I learned how to take blood pressure using a "manual" system (sphygmomanometer cuff, bulb, dial, etc.) and had to understand the theory (i.e., exert pressure on the Brachial artery at 180HG, listen to Korotkoff sounds, watch the reading, etc.).

I understand that blood pressure is measured as the height of a mercury column in millimetres of mercury, which is written down as: mmHg. Hg is the chemical symbol for mercury.

My question is this:
Is it possible for diving pressures on the human body to act in similar to a normal "sphygmomanometer cuff' on the brachial artery? If so, what depth would that occur and what effect would that have?

 

[dlegros]

My instinct would be that this wouldn't happen as when you use a sphyg you apply pressure to a small area.

Underwater, the pressure is exerted over the whole body.

Dom

 

[DiveGolfSki]

My instinct would be that this wouldn't happen as when you use a sphyg you apply pressure to a small area.

Underwater, the pressure is exerted over the whole body.

Dom

True but at what point would the body's internal pressure not be able to compensate for external pressure... I'm sure this is theoritical since we'd probably be long dead by then but I was wondering if anyone knew.

 

[Rick Murchison]

True but at what point would the body's internal pressure not be able to compensate for external pressure... I'm sure this is theoritical since we'd probably be long dead by then but I was wondering if anyone knew.

The reason a pressure cuff works is because of the absence of pressure elsewhere. In other words, there is a place for the fluids to go where the pressure is less than under the cuff, and the vessels collapse.
Underwater, there is no such pressure differential, and, as liquids are incompressible, no such "pressure effect" to be considered. There is no "compensation" required, and no depth at which there would be vascular collapse.
There are plenty of things that'll kill you at depth, but that ain't one of 'em.
Rick

 

[Dr Deco]

Hello DiveGolfSki:

The sphygmomanometer cuff occludes because the pressure is applied locally. Hydrostatic pressure is applied equally over all of the body, and nothing is clamped in any one place on the blood vessel.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[DiveGolfSki]

Hello DiveGolfSki:

The sphygmomanometer cuff occludes because the pressure is applied locally. Hydrostatic pressure is applied equally over all of the body, and nothing is clamped in any one place on the blood vessel.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

Dr. Deco/Rick,

Thanks for the information .... so equal pressure is good ... local pressure is the reason .... guess I'll have to loosen my wetsuit at that critical junction ...

 

[drperi1]

From what I understand, the body is composed of approximatley 98% water, & water (as is the case with all liquids) is virtually incompressible. That is part of the reason why the human body can withstand such great pressure exerted via diving- for example, 132' dive is 5 ATMs of pressure, absolute. However, the body's, and the diver's (mask, for eg.) air spaces are compressible- which is why we feel pain if we do not equalize air spaces at depth, and one of the reasons why we should not dive with any form of congestion- it interferes with equalizing.