<< Predictive Studies Programs

PREDICTIVE STUDIES V (PS V): Oxygen Tolerance and Toxicity.
Major Category: Pulmonary and Neurologic O2 tolerance and toxicity (PS V)

Background: The toxicity of oxygen is the primary factor limiting effectiveness and safety in essentially all forms of diving, and in hyperoxic therapy of decompression sickness. Although oxygen must be considered to have universally toxic properties with effects upon multiple chemical reactions, cells, tissues, and organs, the most apparent limiting expressions of oxygen poisoning in man are pulmonary symptoms and functional degradations, and the nervous system disruptions which can produce generalized convulsions and unconsciousness. They simply represent grossly obvious effects with particular hazard in underwater operations. In the Predictive Studies V Program, extensive investigations for important limiting forms of oxygen poisoning were carried out, and results have been incorporated in the Stress Data Center, with predicted analyses of pulmonary and neurologic oxygen tolerance. In spite of its toxicity, oxygen at high pressures can be safely and effectively used in diving and therapy. An adverse effect of oxygen does not become disturbing immediately, and mild effects disappear when oxygen is discontinued. However, the safe periods for practical use of oxygen breathing are not technically to be considered "Latent Periods," and continuous exposure leads to increasingly severe toxic effect.

Defining human organ tolerance to continuous oxygen exposure. The collaborative Predictive Studies V Program was performed to determine the rates of development and recovery in oxygen poisoning produced by uninterrupted oxygen breathing over essentially the full range of oxygen exposure useful in diving and hyperbaric therapy. A multiyear, multidisciplinary Program investigated measurable physiologic and toxic effects of oxygen upon selected organ and tissue functions at 0.2, 1.5, 2.0, 2.5, and 3.0 ATA of inspired oxygen. Data for ca. 1.0 ATA O2 existed in the Data Center. This Program represents the first systematic investigation of human pulmonary oxygen poisoning at oxygen pressures greater than 2.0 ATA. It also represents the only definitive investigation at pressures greater than 1.0 ATA of oxygen poisoning effects in other human organ systems and tissues, including brain, heart, liver, kidney, skeletal muscle, and endocrine organs.

This investigation of specific organ oxygen tolerance followed over a decade of prior investigations in animals and tissues to assure adequacy of scope and safety in human experiment. The data of the PS V series has permanent usefulness in defining the multiple pathophysiologic effects of continuous hyperoxic exposures. Investigation of human tolerance to continuous hyperoxia additionally served as the required baseline for the subsequent Predictive Studies VI Program which focused on optimal extensions of human organ oxygen tolerance through use of programmed interruptions of oxygen exposure within a useful range of high inspired oxygen pressures.

CONTENTS

08 February 2000 01:29:10 PM