| Popis: |
Oxygen is potentially toxic to all living cells. The nature and the degree of this toxicity are dependent on a number of factors, including the oxygen tension delivered, the duration of exposure, specific tissue variables (blood supply, metabolic rate, immunological defenses), and the susceptibility of the exposed cells to oxygen poisoning (129,249). Because at atmospheric pressures oxygen is a gas and its incorporation into the host is usually by inhalation, the lung, as the portal of entry, is exposed to higher relative oxygen tensions than any other body organ. Thus, at exposure tensions of 1 atm or less, the lung is usually the first vital organ to respond adversely to an increased delivery of oxygen; at exposures of greater than 1 atm, central nervous system damage occurs concurrently with (or may even precede) lung damage (30,64,73,76,83,117,307,342). The ultimate end-point of toxicity, therefore, most commonly is a pulmonary-related death with oxygen administration of 1 atm or less, and a mortality due to combined pulmonary and central nervous system failure caused at higher exposure tensions. Because supplemental oxygen is seldom administered to man at greater than 1 atm pressure, the response of the lungs usually limits the safe use of higher than normal oxygen exposures. |
