OTU's. Where do the limits come from?

[harrison]

List,

I'm wondering if anyone knows how the OTU times are derived. I'm not speaking about the pulmonary "clock" used to determine your percentage of O2 dose over time. For example:

PPO2...Max Single dive exp..........24 hour Exp..........OTU p/Min
.6.................720..........................720...................0.27
.7.................570..........................570...................0.47
.8.................450..........................450...................0.65
.9.................360..........................360...................0.83
1.0...............300..........................300...................1.00
1.1...............240..........................270...................1.16
1.2...............210..........................240...................1.32
etc.

How do we get the OTUp/min numbers? Ie. Where does the 0.27, 0.47 etc come from?

Thanks,
Harrison

 

[BigJetDriver]

List,

I'm wondering if anyone knows how the OTU times are derived. I'm not speaking about the pulmonary "clock" used to determine your percentage of O2 dose over time. For example:

PPO2...Max Single dive exp..........24 hour Exp..........OTU p/Min
.6.................720..........................720...................0.27
.7.................570..........................570...................0.47
.8.................450..........................450...................0.65
.9.................360..........................360...................0.83
1.0...............300..........................300...................1.00
1.1...............240..........................270...................1.16
1.2...............210..........................240...................1.32
etc.

How do we get the OTUp/min numbers? Ie. Where does the 0.27, 0.47 etc come from?

Thanks,
Harrison

With regard to pulmonary oxygen toxicity, an empirical method of computing the dose of an exposure was developed some years ago at the University of Pennsylvania. Each basic unit is called the "unit pulmonary toxicity dose" or "UPTD". A unit dose is the effect of one minute of exposure at one atm PPO2 manifested as a reduction in lung vital capacity. (Bennett and Elliott, 5th)

Ask, and ye shall receive!

Cheers!

Rob

 

[harrison]

Thanks for the quick reply.
If one did not have access to the OTU time chart, is there a math formula known to create them, lets say, based on PPO2 and something else?

Thanks again,
Harrison

 

[The Kraken]

Along the same thread, how does this compare to the % CNS/min ???

PO2 Single % CNS Max
(ATA) Dive /Min Daily Exp
1.6 45 2.22 150
1.5 120 0.83 150
1.4 150 0.67 180
1.3 180 0.56 210
1.2 210 0.48 240
1.1 240 0.42 270
1.0 300 0.33 300
0.9 360 0.28 360
0.8 450 0.22 450
0.7 570 0.18 570
0.6 720 0.14 720

 

[Diver0001]

With regard to pulmonary oxygen toxicity, an empirical method of computing the dose of an exposure was developed some years ago at the University of Pennsylvania. Each basic unit is called the "unit pulmonary toxicity dose" or "UPTD". A unit dose is the effect of one minute of exposure at one atm PPO2 manifested as a reduction in lung vital capacity. (Bennett and Elliott, 5th)

Ask, and ye shall receive!

Cheers!

Rob

Wow. You learn something every day. I always thought that someone at the NOAA just sucked these numbers out of his thumb.

R..

 

[The Kraken]

OK, BJ, just what is, by definition, "lung vital capacity"?
Didn't know I'd end up going to med school, but there it is . . . .

 

[Charlie99]

Along the same thread, how does this compare to the % CNS/min ???

PO2 Single % CNS Max
(ATA) Dive /Min Daily Exp
1.6 45 2.22 150
1.5 120 0.83 150

% CNS/minute is nothing more than the reciprocal of the single dive CNS limit. I.E., at 1.6ppO2 the 45 minute single dive limit can also be expressed at 1/45 min=2.22% / minute. At 1.5ppO2, 120 minutes total clock can also be expressed as 1/120 minutes =0.0083/minute = 0.83%/min, etc.

 

[Spectre]

The exposure limits were derived from clinical tests and experience, not any mathematical based physiological formula.

 

[Charlie99]

OK, BJ, just what is, by definition, "lung vital capacity"?
Didn't know I'd end up going to med school, but there it is . . . .

Various lung capacity terms are defined here.

Vital capacity is a measure of the useable lung volume.

 

[Charlie99]

The exposure limits were derived from clinical tests and experience, not any mathematical based physiological formula.

While both CNS and pulmonary toxicity were empirically determined, per BRW's TDID, the formal definition of OTU is a mathematical formula:

[(PPO2-0.5)/0.5]^0.83 * t. PPO2 in ata, t in minutes. Some references use 5/6 as the exponent rather than 0.83.

The other common long term toxicity calculation, UPTD,

[(PPO2-0.5)/0.5]^1.2 * t give more weight to high PPO2 exposure.

Typical UPTD limits are 1425 absolute max, preferably 800 max per day or 300/day for repeated days.