RMV stands for Respiratory Minute Volume. I don't see any other way to interpret that than as a measurement in volume per minute. E.g. cu-ft per minute. Expressing Respiratory Minute Volume as psi per min does not make sense (to me, of course), as psi is not a unit of volume.
That seems like the "right" answer for RMV (to me).
Yeah, I agree with Stuart.
This has always been something that bothered me, since it seems that critical language like this should have standard definitions. There SHOULD be a "right" answer. Yet I have seen the terms defined differently by different agencies. Here is how I think that the terms should be used:
RMV: Respiratory Minute Volume. This is the volume of gas that a given diver actually moves in and out of their lungs in a minute at any point in the dive. It is dependent on the diver and on depth. In imperial units, cubic feet per minute.
SAC: Surface Air Consumption. This is how much gas a given diver consumes per minute at the surface. It is dependent only on the diver. In imperial units, cubic feet per minute.
SAC x depth in ATA = RMV
I don't know what to call PSI per minute. I guess it's a good thing to know for a particular dive when you are calculating turn pressures for yourself or something. But since it only makes sense in the context of a specific diver, a specific tank and a specific depth, it's not really a useful metric by itself, especially when planning team dives with different tanks, etc...
Baseline: A constant for a given tank, referred to as "K" above - Tank capacity (in CUF) divided by service pressure (PSI). Imperial untis are CUF/PSI
So the one number you really need to know is your SAC rate. Because with that, you can figure out how much gas you will use at any depth, and if you know your tank's baseline, then you can know how fast your SPG will drop.
I don't understand why this can't be standardized throughout the industry.