Real limits of PO2

Gene_Hobbs

Sorry for the delay... I missed this thread and thanks to Benthic for pointing me to it. This is a thesis written by my former boss at Duke. It has some nice references as well as answers to the CO2 and O2 tox question. There are others but this is a nice starting point.

Factors Affecting CNS Oxygen Toxicity in Humans
Natoli and Vann, 1996
RRR ID: 123456789/21

Abstract:
The onset time of central nervous system (CNS) oxygen toxicity symptoms is reduced by elevated oxygen partial pressure, inspired CO2, immersion, and work. This project investigated the effects of these factors in humans on ventilatory response to CO2, brain cortical oxygenation, and the occurrence of symptoms of CNS oxygen toxicity. Relative changes in cerebral oxygenation from a baseline were measured by near-infrared (NIR) spectroscopy. Ventilatory response was measured during CO2 rebreathing in a computer- controlled, closed-circuit breathing apparatus. The results of this study suggest that inspired C02 is a potent instigator of CNS oxygen toxicity, more potent than oxygen alone or in combination with immersion and work. Thirty-three of the 35 CNS oxygen toxicity symptoms reported, including a convulsion, involved breathing inspired C02 at a Pio2 of 2.80 ATA. Most (31) symptoms were reported while the inspired CO2 was 7.0% -7.5%. Hyperoxia, Pio2= 1.75 or 2.80 ATA, leads to increased cerebrovascular oxygenation despite vasoconstriction. Inspired CO2 reversed vasoconstriction and increasing cerebral oxygenation further. Subjects with symptoms consistent with oxygen toxicity did not show a CO2-induced vasoconstrictive reversal despite increased cerebral oxygenation. This result is contrary to previous findings (Lambertsen 1955) where inspired C02 caused symptoms of CNS oxygen toxicity while increasing cerebral blood flow and increasing cerebral oxygenation. This disparity is most likely due to the difference in the cerebral oxygenation measurements made. NIRS measures regional physiology while cerebral blood flow and blood sampling measurements are global physiological measurements. Ventilatory response to CO2 did not correlate well with symptom incidence but the subject who convulsed had the lowest ventilatory response to CO2 with a Pio2 of 0.21 ATA. The subject who convulsed also had the largest increase in cytochrome a,a3 oxidation with inspired Cog. The combination of the low ventilatory response to CO2 with increased cerebral oxygenation resulting in an oxygen seizure supports the hypothesis that susceptibility to CNS oxygen toxicity may be related to CO2 retention as a result of depressed ventilatory response to CO2 (Lanphier 1975). Facial immersion lead to increased cerebrovascular blood volume and cytochrome a,a3 oxidation at both 0.21 and 2.80 ATA Pio2 and with both positive and negative static lung loads.

As for high pO2's, it is hard to beat Ken Donald's work "Oxygen and the Diver" (if you can find a copy).

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"Oxygen is addictive and deadly. Everyone who uses it will eventually die" --RW Hamilton, PhD 1991

Abbo

Kenneth Donald: Oxygen & the Diver. Prices quoted on Amazon range from $495 (+P&P) up to $1,040.55 (+P&P). I'm feeling a little too inpecunious for that right at the moment. It's a pity there isn't a Wiki facility on Rebreatherworld: the subject keeps coming up.

Gene_Hobbs

WorldCat lists the book in 23 libraries workwide.

UHMS members have access to the copy in the Duke University Medical Center Library.

Other libraries (listed twice in the DB):
US,CA ALIBRIS ALBRS
US,FL BARRY UNIV FBC
US,HI UNIV OF HAWAII AT MANOA HUH
US,MA HARVARD UNIV, MED SCH, COUNTWAY LIBR HMS
US,MA MARINE BIOLOGICAL LAB/WOODS HOLE OCEANOG MBW
US,OH BAKER & TAYLOR BAKER
CA,QC CONCORDIA UNIV LIBR CDN
Ireland TRINITY COL, DUBLIN ERD
South Africa SABINET SZT
South Africa SANDF Z6Q
South Africa SOUTH AFRICA NAVAL REF LIBR Z6O
South Africa UNIV STELLENBOSCH-MED LIBR Z8Q
United Kingdom BRIDGEND LIBR AND INFO SRV UKBRD
United Kingdom BRITISH LIBR UKM
United Kingdom BRITISH LIBR BRI
United Kingdom CAMBRIDGE UNIV CUD
United Kingdom KENT CNTY COUNCIL ARTS & LIBR UKKCC
United Kingdom UNIV OF OXFORD

and

US,CA UNIV OF CALIFORNIA, SAN DIEGO CUS
US,MD NATIONAL LIBR OF MED NLM
US,MD US NAVAL ACAD UNA
US,SD UNIV OF SIOUX FALLS

__________________
http://rubicon-foundation.org/
Home of the Rubicon Research Repository.
For help getting started with the Repository, please visit our FAQ page. PLEASE support our work.

"Oxygen is addictive and deadly. Everyone who uses it will eventually die" --RW Hamilton, PhD 1991