Overshooting NDL and mandatory deco stops

[dmaziuk]

I cannot easily add a 2nd x-axis to my graph.

Putting metric buckets into a 2nd column, then populating the 3rd column w/ concatenated "standard" and metric ones (=A1&" "&B1), then plotting with that as X-axis, might work.

Edit: newline should be better: =A1& CHAR(10) &B1

 

[Blackcrusader]

Now that I see that my .3 cf/m equals 8.5 L/m and BlackCrusader's is 6.85 L/m, I can see why his causes some consternation. I don't think I've been diving with anyone who has a lower consumption than mine, and I'm a petite female. Though I have been diving with even some males who have about the same consumption.

It does sound like, though, from BlackCrusader's videos, that he breathes very shallowly. It was a little painful to listen to him suddenly and quickly take a partial breath, then exhale extra slowly but not deeply, then take a quick partial breath again. I do believe he may be retaining CO2. It might be better to breathe a bit more "normally". It's ok to have 8 or 10 or 20 L/m.

If you read my posts about every 2 minutes I take a couple of full breathe intakes and exhale immediately... If I was retaining CO2 I would think that over a 40 dive trip in 2 weeks I would be feeling the affects on any dive. I don't need to put a bag over my head to see what CO2 buildup feels like. My breaths aren't sudden, they are planned, sudden sounds like I am out of control lol. I breath very slowly but I do fill my lungs to what you would normally do even when not diving. I do not like to inflate my lungs where you go beyond your normal intake. We can all breathe in and completely force in more air than normal.

 

[Blackcrusader]

@rsingler and others...So what are the physiological factors that predetermine gas consumption? Things we have little control over. Is it the individual’s metabolic rate (and the resultant need to eliminate CO2) that is the primary factor for gas use and therefore the SAC/gas consumption rate? Why then do women seem to have lower rates?

A lot of women have smaller lung capacity as well.

 

[Blackcrusader]

So do all those things you were taught, to relax and streamline. Breathe fully (not shallowly) to minimized dead-space ventilation, and accept what you get. We just can't all be like @scubadada and Crusader, sad to say.

Yup I think being relaxed is a key thing. I see many divers who are not fully relaxed on their dives. Maybe I over relax

 

[Blackcrusader]

I have found the SAC on the Teric screen to be not useful and have deleted it from my home screen. The gas consumption data at the end of the dive is much more useful.

I decided not to get the AI for my Perdix. Really just another distraction for me I think. On a dive vacation in November my DM guide was working on his birthday. He has around 12000 dives and is an average sized Pinoy man. Around five foot 5 and weighs around 65kg. So anyway the dive center is doing some island trip but the DM and I are doing a fun dive near the shore. So I asked the dive center owner if we could just enjoy ourselves and dive to 50 bar. He's all for it. So on our dive we decide to do a wreck dive then finish the rest of the dive along a reef wall before heading up for the safety stop. Now this DM is slightly better on air than I am. I think sometimes within 5 or 10 bar on each dive but that could also be tank fills being slightly different. Great guide and diver to be with as well. He does around a thousand dives a year.

So we did a max depth 34m, 93 minute dive. My 12l tank 210 bar start 50 bar finish. It really was a slow relaxed fun dive. It was our 65th dive together in a few weeks of diving. So we are really relaxed with each other.

 

[Blackcrusader]

I have found the SAC on the Teric screen to be not useful and have deleted it from my home screen. The gas consumption data at the end of the dive is much more useful.

You might consider the Cressi Digital2 console. I posted a picture of it. One thing it does is shows Range... this simply means that from any point on the dive it calculates your current depth and air to 50 bar and time remaining. It's not a dive computer but it is an easy console to read. So lets say you are going to do a dive at 20m along a wall that meets the seabed, you can see that you will have more than enough time to even get to zero NDL and still have more than 50 bar left so you can come up to shallower depths before the safety stop.

 

[rsingler]

Well, that was interesting! I guess I'm a "normal responder", lol! That was NOT fun.

I had one of my buddies monitor me while I hooked myself up to an ECG and anesthesia machine with no CO2 absorber in the circuit. I ran only maintenance oxygen (300 ml/min), and hooked myself up to an oximeter as well as ECG. As I rebreathed in an oxygen-filled circuit with no CO2 absorption, my inhaled CO2 rose as I produced it.
I'm a 69 y/o, 67 kg, 5'10" guy with an average physique, in good CV health.
I ran two tests: I lasted 5 minutes in the first run, and 7 minutes in the second before bailing out. The table below shows the second test. My baseline pulse had risen from 51 to 63, and I had a bit of a headache from the first run (which didn't start until about 3 min after I bailed the first time). It took about 8 min to get back to my baseline of 5.1 l/m RMV sitting in a chair between tests.
Table parameters are as follows:
-Time (minute)
-Inspired/exhaled CO2 (mm Hg)
-Minute ventilation in liters/min
-Pulse
-Anxiety on a scale of 0-5, where 5 would be almost panicking

Second run results:
0 - 0/39 - 5.1 - 63 - 0
1 - 6/42 - 6.3 - 69 - 0
2 - 15/42 - 7.1 - 65 - 0
3 - 31/45 - 7.9 - 66 - 1
4 - 35/47 - 9.4 - 67 - 2
5 - 45/51 - 13.9 - 67 - 3
6 - 53/55 - 18.5 - 70 - 3
7 - 55/58 - 22.5 - 74 - 4, with dizziness
Oxygen saturation 100% throughout.

Writing this about a half hour after the tests, I still have a mild headache, but otherwise feel fine.

Noteworthy (and just as they taught in med school) was that with a 50% increase in my end-tidal CO2 (39 to 58), my minute ventilation quadrupled! Now imagine that happening at depth due to exertion, with thick air and a poorly tuned regulator, which, coupled with your skip breathing practice, caused your CO2 retention in the first place. Can you stay calm enough to get yourself both out of difficulty and eliminate your hypercarbia? Do you have enough gas at depth to handle 4x your nominal requirement?

That was interesting!

 

[rsingler]

@rsingler and others...So what are the physiological factors that predetermine gas consumption? Things we have little control over. Is it the individual’s metabolic rate (and the resultant need to eliminate CO2) that is the primary factor for gas use and therefore the SAC/gas consumption rate? Why then do women seem to have lower rates?

It's been almost forty years since I was on a university medical faculty, so I'm the wrong person to ask, lol! If I had to speculate, I'd say that two of us with the same size but different sex have differing high consumption compositions. Women may have smaller muscle mass (high consumption) and larger fat mass (low consumption) for identical weight.
On the other hand, propelling the same mass thru the water takes the same amount of energy, so if a man and a woman of identical mass had differing RMV, I guess I'd invoke more efficient gas exchange. Since we know it's not the oxygen requirement driving the breathing, if a woman's anatomy favored CO2 elimination, she would need a lower RMV. Indeed, (and this is pure speculation) having smaller lungs may in itself favor gas exchange, since there's less dead space to ventilate.
There are also small differences in Basal Metabolic Rate, but not enough to account for the differences I've seen.

But really, I have no idea why my wife is able to keep up with me and use less air. One of the many injustices of married life...

 

[Mike1967]

What do you use if for?

I use it to keep an eye on my breathing rate every now and then.

This ^

 

[Jay]

But really, I have no idea why my wife is able to keep up with me and use less air. One of the many injustices of married life...

A valuable quote ... I guess your wife's not on SB. Don't worry, your SB friends know that what's written on SB stays on SB (or something like that ...) ... perhaps ...