Briefly describe the possible effects on the respiratory system when a normal person breathes 100% oxygen at sea level under normal atmospheric pressure.

Essay:

            Once alveolar PO₂ rises above a critical level, the hemoglobin-oxygen buffer is no longer capable of keeping the tissue PO₂ in the normal safe range between 20 and 60 mmHg. High arterial PO₂ causes acute oxygen poisoning with symptoms like nausea, muscle twitchings, dizziness, disturbance of vision, irritability, disorientation, seizures and coma.

            The toxicity seems to be due to the production of the superoxide anion O₂^-, which is a free radical and hydrogen peroxide. When 80-100% oxygen is administered to humans for periods of 8 hours or more, the respiratory passages become irritated, causing substernal distress, nasal congestion, sore throat, and coughing. Exposure for 24-48 hours causes lung damage as well. The reason oxygen produces the irritation on the respiratory system is not well understood, although oxygen treatment appears to inhibit the ability of lung macrophages to kill bacteria, and surfactant production is reduced.