Breathing difficulties while diving

Question
Hello,
I recently started Scuba Diving and obtained my Open Water through PADI.  I took my open water in Georgian Bay where the water is quite cold.  We completed six dives that weekend, where two dives I had trouble breathing.  I am aware that I am getting air and kept my breathing steady (listened and watched the bubbles), but I felt like I couldn't breath.  
I heard from a friend of mine that is experienced in diving that I may not be exhaling properly and Carbon Dioxide could be building up in my lungs.  To combat this, he recommends really pushing the air out during my exhales.  I have yet had a chance to try this.  
On the dives that it happened, out of the blue I thought "I have to surface", and then that's when I couldn't breathe.  It came out of no where as I was actually having a good time under the water.  Both times I didn't surface, I just stopped and focused myself.  Also, I noted it happened on the afternoon dives, maybe I was tired and didn't realize it?
Another problem is that I went through a ton of air during these experiences.
I am heading to Cozumel in Feb and will be taking the Advanced course.  I don't want this to happen there too.

Any ideas of what is happening and any advice?

Thank-you!

Answer
Laurie,

Welcome to the world of SCUBA!

When underwater, especially in a cold water environment, there's a lot going on both physical and psychological.

I'll start with the easiest issue first.  The air consumption rate for beginning divers is almost always excessive.  We refer to the condition as "air pig" (just some SCUBA humor).  This is very normal and will get better with experience.  As you become more comfortable under water, you will use much less air.

I think you are on the right track in noticing that the shortness of breath was occuring on later dives.  Being tired will contribute to excessive air use.  In addition, the cold water environment makes much greater demands on the body, so fatigue will happen quicker in cold water.

Yes, if your exhalations are not adequate, you can experience a build-up of CO2, but the build up is in the blood, not the lungs.  This build up will trigger the instinct to breath.  Your friend's suggestion of focusing on the exhalation is a good one, but you don't want to be so forceful that you are causing hyperventilation either.  Just try to keep your breathing steady and don't hold your breath.

Cold water will also cause you to tense up and that might be interferring with your breathing.  You could also consider the possibility that a tight fitting wetsuit may be restricting the expansion of your chest during the breathing cycle.

Your instincts are very good.  If you feel that you are not getting enough air, stop, don't panic, get your breathing under control, and check your gauges to make sure you have an adequate air supply.  Be sure to signal your dive buddy, and if need be make a slow, safe ascent.  Panic will definitely affect your breathing rate, and can turn into a vicious cycle of poor air exchange, more panic, etc.

You will definitely have a different experience diving in warm water.  Almost all the things you were experiencing in the cold water will not be happening in the tropics.  Be sure to address any air consumption concerns with your Advanced Diving instructor before getting in the water.

SCUBA is like most other skills; you will become more comfortable as you get more experience.  Think about when you learned to drive a car, there were so many things happening at once:  Gas, brakes, mirrors, turn signals, etc.  But that eventually became second nature and you don't consciously think about those things anymore, they just happen.  SCUBA diving will progress the same way.

I hope this helps, and have a fun, safe time this winter in the tropics,

Henry Babcock
AllExperts SCUBA Expert