Easier to breath = higher SAC rate ?

[trappist]

I just bought a Mk25/A700 and did my first dive with it last WE. Now this was not the ideal dive to compare breathing and consumption (quite rough sea), but I was wondering if an easier to breathe kit would actually lead to higher SAC rate ?

My first reaction would be no... as higher SAC rate means more volume of air inhaled while easier to breath is not the same concept.
My second reaction is, well if easier, you can definitely get more air out easily !
and my third reaction is to get back to the first one !

What are your thoughts on this ?

When I will have a few more decent dives on this reg, I will be able to compare the SAC rates for real, but in the mean time, it does not hurt to make our brains work out ;o)

 

[Jimmer]

I have absolutely NO proof of my opinion, but going by "feel", I find that an easier breathing reg, actually lowers my SAC rate. My basis for this, is that when a reg is effortless to breathe off of, especially in tougher diving conditions, I don't have to work at getting a lung full of air, which means I can stay more relaxed, and not physiologically require a higher rate of respiration.

Might be total BS, but that's my impressions!

 

[HIGHwing]

If we're talking notional evidence, my SAC rate (per my VT3) is least when I dive my Atomic ST1 which at the lowest setting breathes easier than I would like. I find that having a reg I physically can not "over-breathe" is an excellent way to keep the psychological factor of the SAC rate in check. The real magic of SAC rate is mental, equipment, technique, and fitness in my experience.

Interestingly, I've found the biggest factor changing SAC rate was taking the Peak Performance Buoyancy Specialty. Sometimes the best modification to equipment is the user.

 

[Bubbletrubble]

I'm inclined to agree with Jimmer.
Easier breathing reg (to a certain extent) = more relaxed breathing = lower SAC rate
To elaborate a little, an improperly adjusted reg, e.g., with a cracking pressure set too high (higher than manufacturer specs), may cause one to expend more effort while breathing. This can affect the rate and volume of respiration (possibly leading to panic) -- all of which could negatively impact the SAC rate.

It should be noted that if the reg is tuned to breathe too easily, e.g., cracking pressure set too low, this may increase the probability of freeflow. And, of course, freeflow will negatively impact your SAC rate.

To clarify, cracking pressure isn't the only reg adjustment/variable that affects subjective ease of breathing. It only describes how easy it is to initiate a breath on the second stage for a given intermediate pressure delivered by the first stage. Some of the "overbalanced" first stage designs can make it feel like the reg is "force feeding" air at depth once flow is initiated. This is one feature that would seem to increase ease of breathing...but if it's excessive (providing more air than the user needs/wants), it can actually negatively impact SAC rate.

I hope my post isn't too confusing.

 

[ptyx]

One more for easier breathing = lower SAC.

I've also noticed that when I'm on a poorly tuned regulator, I tend to breathe deeper and less often. Which I heard is less efficient in term of pulmonary gas exchange. But at this point I'm combining anecdotal evidence with random medical theories gathered on the internet

 

[RJP]

One more for easier breathing = lower SAC.

I've also noticed that when I'm on a poorly tuned regulator, I tend to breathe deeper and less often. Which I heard is less efficient in term of pulmonary gas exchange. But at this point I'm combining anecdotal evidence with random medical theories gathered on the internet

+1

Two reasons:

As stated above, you will naturally "breath easier" if its "easier to breath"

Additionally, you cannot "over consume" air by delivering it to your lungs efficiently on a "volume per single breath" basis. Taking "more breaths per a given period of time" is another story...

As an analogy: You cannot "walk too fast" by simply increasing how far you go in a single step. It's the succession of the steps you take - how many, and how much time between them - that determines your speed.

:cool2:

 

[Stu S.]

Work of breathing is measured as joules per litre, or j/l. One litre is about the volume of one breath. A premium regulator will have a work of breathing of about .8 j/l and a cheapie will be maybe 1.8.

How much work is that extra joule per breath? Walk up a flight of stairs. Then walk up the next flight with a penny on your pocket. The extra work of carrying the penny is about 1 joule. Not big work. It has been described as one hundredth of the energy a person can receive by drinking a drop of beer.

A joule is a tiny amount of energy, compared to the overall work of a diver. So, even though that easy breathing reg feels like a lot less work, it is more feel than fact. (If you had a reg so damaged that you had to suck on it until you choke that's different.)

Anyhow, if you want to improve your air consumption, there are more effective ways than changing regulators.

 

[Atomic_Diver]

+1 Two reasons: As stated above, you will naturally "breath easier" if its "easier to breath" Additionally, you cannot "over consume" air by delivering it to your lungs efficiently on a "volume per single breath" basis. Taking "more breaths per a given period of time" is another story... As an analogy: You cannot "walk too fast" by simply increasing how far you go in a single step. It's the succession of the steps you take - how many, and how much time between them - that determines your speed. :cool2:

But I thought speed= distance/time...

 

[miketsp]

One more for easier breathing = lower SAC.
I use a Micra ADJ and I open the setting until it's just a fraction below free-flow. For the rest of the dive I forget I'm breathing through a reg.

 

[RJP]

But I thought speed= distance/time...

It is. Which is precisely why you cannot "walk too fast" simply by increasing the length of one stride. That's only distance.

:shocked2: