Do you really have to exhale while ascending?

[downdeep]

You don't have to exhale if, like President Clinton, you didn't inhale.

You crack me up.

 

[Rick Murchison]

... We have ARDS patients on ventilators who require very high inspiratory pressures to inflate their lungs. They often get pneumothoraces, but they don't get air embolism. It's always bothered me, this disparity.

I think you'll find that "very high inspiratory pressures" are on the order of a few inches, not feet, of water pressure. So it's an apples to oranges comparison - no disparity
Rick

 

[Rick Murchison]

Rick, what do you teach now?

My plan for my next dive was to try and get my bouyancy down at the end of the dive, with 200 lbs of air in the tank and an empty BC.

That way, for normal dives ending with 500 lbs psi, I'd be a little heavy.

Empty BC and end-of-dive gas (for OW class, about 13CF - 500 psi in an 80) at the surface. This ensures the ability to remain neutral all the way to the surface and retain fine control over ascent rate all the way from the safety stop to the surface - which is, as has been previously said, the most critical part of the ascent w/r/t both DCS and overexpansion injuries. 13CF weighs about a pound, which you can easily handle with breath control - I wouldn't worry too much about the difference in 500 and 200 psi - about half a pound in an AL80.
Rick

 

[Rick Murchison]

True with one exception.
In cold water diving with neoprene exposure there's a risk of being negatively boyant at certain depth. Depending the volume of the wetsuit material and volume of the BC it can be as shallow as around 70'. The couple of pounds less ballast one would have in this case increases this depth to about 100'.

You need a new BC... or a dry suit. What you describe is the wrong equipment for the dive, and I don't recommend your solution.
Rick

 

[NJMike]

Interesting, Rick, and makes sense too...empty BC, end of dive gas...at the surface, not at safety stop depth. That way you do not become positively bouyant at any point from the safety stop to the surface.

That piece of advise was worth the entire thread!

 

[jupitermermaid]

One thing that I've learned through diving with buddies (NOT IN CLASSES, UNFORTUNATELY), was that buoyancy control was determined by the amount of lung capacity used (or not used) during descent and ascent. Weight issues was much more easily controlled by being able to control the lung capacity used for breathing rather than weight used, holding, or exhaling breath. What a difference it made in my diving pleasure, extension of down time, and ability to control ascent and hold trim for depth.

 

[cowdog77]

"I'm willing to be weighted such that I'm breathing towards the empty end of my lung capacity during that final slow ascent."
_____________________
Ditto, that works for me.

 

[redrover]

Since you only need to be in the 10' to 0 foot range for a minute or so, I'm willing to be weighted such that I'm breathing towards the empty end of my lung capacity during that final slow ascent.

I'm unable to 'get' what you said in bold. Would you please explain it or say it diffrently?

 

[Meng_Tze]

Anecdote:

When I learned to dive it was through a PADI discover scuba experience. 2 hrs in a pool, then a dive with a DM to a max of 12m (38ft or so). Nice fishies, reefs and lobsters. Enjoyed it so much I hired the DM for another three dives. During these dives, I regularly found myself with my feet at the surface, breaching the surface and the next minute I was back down at the bottom. As you can tell...... buoyancy sucked. In fact was non-existent.

Afterwards, in a restaurant talking about dives..... my chest hurt a bit. I thought it was because I strained myself. The next morning every breath hurt slightly and deep breaths were difficult...... lung over expansion. In less than 40ft over four dives I managed to hurt my lungs.

The pressure change was a little over 1 ata, imagine what more pressure difference can do. So, exhale, keep an open airway ascending

 

[Charlie99]

Since you only need to be in the 10' to 0 foot range for a minute or so, I'm willing to be weighted such that I'm breathing towards the empty end of my lung capacity during that final slow ascent.

I'm unable to 'get' what you said in bold. Would you please explain it or say it diffrently?

As you breathe in and out your buoyancy will change by several pounds. Full lungs are much more buoyant than near empty lungs.

My preference when using 3mm or 5mm wetsuits is to be neutrally buoyant --
at 15' depth
near empty tank
no air in BCD
lungs near full -- i.e inhaled close to the my normal maximum inhale

As I ascend towards the surface my wetsuit will expand and add buoyancy. I compensate for this additional buoyancy by not fully inhaling. In other words, I am willing to exhale and then do shallow breathing for the short period it takes to do a slow, controlled ascent over the last few feet to the surface. In reality I still will do fairly large breathing cycles, but I just spend more time with my lungs near empty and relatively little time with my lungs nearly full.

I'm willing to do this in order to reduce the amount of lead I carry by 3 or 4 pounds. This reduction in lead means that I have that much less air in my BCD throughout the dive, making buoyancy control easier.

Charlie Allen