Breathing and buoyancy

[Peter Guy]

I used to breath continuously underwater after misinterpreting "do not hold your breath phrase" when I started diving and my air consumption went though the roof. I do not breath continuously on the surface as a matter of fact. When I switched to my normal breathing my consumption fell as much as 2 times and it became much easier for me to be stable underwater.

Thank You! It is unfortunate that so much is said about "Never Hold Your Breath" while diving -- which is, of course an EXTREMELY IMPORTANT CONCEPT but is key only when ascending. While people are drilled to "NEVER HOLD YOUR BREATH" the reasoning behind such is often understated so newer divers never internalize the reason for the rule.

Taking big breaths, and, yes, holding them, to stop a descent is a valid and necessary skill. And, gulp, taking a deep breath to start an ascent also works -- the key here is the notion of STARTING the ascent and NOT closing your airway.

Which gets back to the OP's issue which appears to be about the lag time between having a volume change in lungs (or BC -- both are air bladders) and the time when you start to ascend or descend. We have quite a bit of mass underwater and the small changes in displacement volume (which occurs when inhaling or exhaling) take time to overcome the inertia of our mass. And yes, it comes with time and practice (at least good practice!).

 

[elan]

Well, if you understood "do not hold your breath" to mean "eliminate the split second pause while the body switches from inhale to exhale to inhale", then I understand but wonder what the Instructor said when you questioned this. However, that is an extremely dangerous way to dive which, for most people (not you though I suppose), would lead to hyperventilating and possibly a build up of CO2 in the system. The pause between inhale and exhale when done as normal process for breathing, is in my layman's terms, the body's split second reconfiguration from Inhale to Exhale. It is not holding your breath. What you imply is that there is no need to inhale or exhale at all as long as you keep an airway open. Keeping an airway open but not breathing is, IMO, BOTH not breathing AND holding your breath even though it will, in theory allow for the air in your lungs to compress and/or expand according to your position in the water column and the associated pressure.

Breathe Normally says it all.

Steve, while the split second thing is true about switching from inhale to exhale I found the I may have pauses around 3-4 seconds between exhaling and when I want to inhale again. That's on the surface when I do moderate calm work. After getting some dives and starting breathing underwater close to how I breath on the surface I noticed my consumption dropped, I can control buoyancy better and I never got any headaches as inhale when I want to and I believe when I want to breath that's when my body wants to get rid of the excess CO2, so I do not worry about the build up.

 

[gypsyjim]

I believe the worry is not so much build up of CO2, but lung expansion injuries that can result from even short ascents when airways are closed, ie: holding breath? Smooth, continual and normal breathing is the key to avoiding this

 

[Solly]

thanks folks for fixing the notion of lung volume, after a second thought it makes sense, one only uses the BC to compensate for +ve buoyancy loss due to wetsuit compression and I agree that lung volume is used for fine tuning.... I am trying to remember how it was through my last dive but this was few weeks ago... I will go dive and think about this underwater

 

[gypsyjim]

Solly, this has been both fun and educational.
Relax, have fun, and play around as you learn. Never be afraid to ask questions like you have here.
Just be prepared to sort threw the responses for the parts that fit and ring true for you. As expressed throughout this thread, it's blend of both science and art. You do need to understand the physics to whatever degree fits your learning style, because there is a lot going on, but once the body becomes comfortable the "art" part comes more naturally, only with experience.
I personally never stop thinking about the mechanics while diving, I never stop playing with my buoyancy, and I know that I am just touching the surface of what there is to know about this sport! It has changed and grown so much since that first dive in '70, and it never ceases to amaze me what I don't know!
That is one of the things about diving that keeps me coming back. That and all the great people we meet in this sport.

 

[Thanshin]

Thanshin, you have it exactly right. THIS thread from Rick Murchison goes into more detail.

Nice link. I understand it much better now and it's nice to have the actual numbers and formulas.

 

[Thalassamania]

To put it in your terms: I set my midpoint at about 4. I cycle from 2 to 6. If I want to go up I move the midpoint to 5, or even 6. If I want to descend I'll move the midpoint analogously downward.