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CO2 Narcosis Study

Hypercapnia: Cognitive Effects and Monitoring

Statement of the Problem

To better define the human physiology of CO2 elimination at depth in order to avoid CO2 narcosis and cognitive impairment, this series of experiments will: 1) test and quantify the interaction between the CO2 O2 and N2 induced effects on cognition in order to construct an algorithm to compute “equivalent narcotic depth” based on inspired partial pressures of these gases; 2) establish the relationship between end-tidal (PETCO2)and arterial PCO2 (PaCO2)in the upper range of interest (50-70 mmHg) during rest and immersed hyperbaric exercise in order to construct an algorithm to predict PaCO2 from PETCO2; 3) test the accuracy of two small end-tidal and transcutaneous PCO2 monitors (Polestar Technologies Inc., Alexandria, VA) against PaCO2 in immersed exercising divers.

Hypotheses

We propose to test the following 4 hypotheses:

  1. An algorithm can be developed which predicts cognitive performance in immersed exercising divers, based on the PETCO2 and the diver’s inspired partial pressures of oxygen and nitrogen (PIO2 and PIN2).
  2. PETCO2 using mass spectrometry is an accurate estimate of PaCO2 at rest and during immersed exercise and can be used as a PaCO2 surrogate at levels exceeding 50 mmHg and depths up to 158 fsw (gas density 6.4 g/l, similar to 165 fsw density of 6.8 g/l).
  3. PETCO2 can be estimated during immersed hyperbaric exercise using a portable transcutaneous CO2 analyzer (Polestar).
  4. The transcutaneous PCO2, measured using a Polestar (Alexandria, VA) device, will accurately reflect PaCO2 in immersed exercising divers at levels exceeding 50 mmHg and at depths up to 158 fsw.

Navy Relevance:

•Results could be directly translated into new guidelines for PETCO2 limits as a function of gas PIN2 and PIO2.
•PCO2-N2 interaction guidelines would be immediately available to the Fleet upon delivery of the final report.
•The accuracy of a portable monitor is directly assessed.

 

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