H. Bardin and C. J. Lambertsen

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1 . nttp://archive.rubicon-foundation.org A Quantitative Method for Calculating Cumulative Pulmonary Oxygen Toxicity Use of the Unit Pulmonary Toxicity Dose (UPTD) H. Bardin and C. J. Lambertsen Institute for Environmental Medicine University of Pennsylvania April, 1970

2 nitp://archive.rubicon-foundatjon.org In analyzing the development of pulmonary oxygen toxicity under changing conditions of pressure and exposure duration, it is helpful to use a "unit pulmonary toxicity dose" (UPTD). One UPTD is defined as the degree of pulmonary toxicity produced by breathing pure oxygen at a partial pressure (P 02 ) of 760 mm Hg (1 ata) for one minute. This same toxicity can be achieved by exposure to various other combinations of P and time. 02 It is here assumed that the lowest P which will produce a demonstrable pulmonary toxicity within some finite 02 time is 0.5 ata, i.e., the asymptote of pressure on time is 0.5 ata. In this situation all combinations of P and time 02 which have a toxicity of 1 UPTD fall along a curve log (P -. 5 ata) = m log t + log b (1) which may also be written where P -:-. 5 at a = btm p = inspired Po2 in ata t = time in minutes b = intercept constant for t = l m = slope constant (2) Breathing 1 ata P 02 for two minutes produces 2 UPTD. Once again, there is a curve of form (2) whi ch includes all combinations of P 02 and time. This curve is consider ed t o be parallel to the first, i.e. t he slope constant ''m" is

3 ' -2- the same in both equations. Otherwise, at some pressure, an increase in 0 2 breathing would le~sen toxicity. The intercept constant '~", on the other hand, will be larger for 2 UPTD's than for 1. This concept can be extended to any number of UPTD's (Figure 1). One of the effects of a toxic dose of P 02 is to decrease vital capacity. Since all poin~along a curve of form (2) represent the same pulmonary toxicity dose, the points on one curve also represent the same influence of oxygen exposure upon vital capacity. Clark has plotted equal toxicity curves (Figures 2 and. 3) for the following /... doses: Corresponding 6VC in UPTD 50% of subjects The 6 VC response to varying "doses" of oxygen exposure is not a linear function, but rather the classical sigmoid dose-response curve (Figure 4). All lines of equal pulmonary toxicity are linear (on I./ l og-log transform), are parall el, and have the same

4 -3- asymptotes of 0 time and 0.5 ata. Therefore, any p 0 2 x time exposure can readily be converted into UPTD units, and these units are for the present considered to be additive. To convert from an exposure of P 0 2 = P 2, time = t 2, to a dose of equal toxicity at some P 1 and t 1, we get P -. 5 ata 1 = bt 1 m [from (2)] P -.5 ata bt m 2 2 (3) or tl = t2 P ata p2-.5 at a (4) If t 2 is expressed in minutes, then the toxicity of exposure ~.../ (P 2,t 2 ) in UPTD units is given by. 5 ata (5) On the basis of the empirical evidence now available, the choice of a value,currently is reasonable. "pulmonary index". m = ) (6) This, the slope constant, also is called a The toxicity expressed in UPTD is sometimes referred to as the "sea-level equivalent" or "1 ata equivalent" oxy.gen toxicity. l.. / Figures 5 and 6 illustrate the cumul ative buildup of

5 l:lttp://!irc/'rive.rubicon-foundation.org - 4- pulmonary toxicity, as measured in UPTD's during Prototype Decompressio~s I and II for the Tektite II 100-foot opensea project. This report dra'>vs heavily on the PhD theses of J. N. Feld (in preparation) and J.M. Clark (University of Pennsylvania, 197_0). I. /

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7 rubicon-foundation.org \ Figure 2 : Seven selected curves of differing but constant toxicity. PULMONARY OXYGEN TOLERANCE CURVES IN NORMAL MEN (BASED ON VITAL CAPACITY CHANGES IN 50% OF THE SUBJECTS) sn11aol t::..vc 0-2% X - 4% f:. -6% 0-8% f:. -10% 0-15% 0-20%.J <i: a... (/) z O.l, DURATION O( OXYGEN BREATHING (hours) From: J.M. Clark PhD thesis, p.l64, Fig. 18A.

8 Figure 3 PULMONARY OXYGEN TOLERANCE CURVES IN NORMAL MEN (BASED ON VITAL CAPACITY CHANGES IN 50% OF THE SUBJECTS) ~.0 - E <t - (.0 l!..' c:::: ::::> (/) (/) w a= a. :3.0 _J <l: ~ c: ~ w z 2.0 (!) >- X 0 0 l!.: c: "- 1.0 (f) z 0 0L-~ L ~,~o ~, 5~ ~2~o~ ~2~ ~3~o DURAT ION OF OXYGEN BREAT HING (Hours) F rom: J M Clark PhD t hesis, p. 165, Fig. 18B.

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SPUMS Journal Vol 27 No. 1 March

SPUMS Journal Vol 27 No. 1 March 1997 43 TOLERATING OXYGEN EXPOSURE R W (Bill) Hamilton Key Words Hyperbaric oxygen, oxygen, physiology, unconscious. The fact that oxygen can be toxic is well known to