What causes pulmonary O2 toxicity at low pressure?

Pulmonary oxygen toxicity at low pressure is primarily caused by prolonged exposure to elevated partial pressures of oxygen (PPO2). When divers breathe oxygen at higher than normal levels—typically above 1.4 ATA (atmospheres absolute)—for an extended duration, it can lead to the development of pulmonary oxygen toxicity. This toxicity manifests itself through symptoms such as coughing, chest pain, and difficulty breathing, as the high levels of oxygen can cause damage to the lung tissue.

Oxygen, while essential for life, can become toxic at elevated pressures and concentrations, especially when the exposure is sustained. The risk increases as the duration of exposure to high partial pressures extends. Thus, in the context of diving, even at lower ambient pressures, if a diver is exposed to high levels of PPO2 for a significant amount of time, the likelihood of experiencing pulmonary oxygen toxicity increases.

This understanding highlights the importance of managing exposure times and monitoring oxygen levels during diving activities, especially when using mixed gases or when diving for extended periods.