Problem 48 - Chemistry A Molecular Approach

Question

Scuba divers breathing air at increased pressure can suffer from oxygen toxicity-too much oxygen in their bloodstreamwhen the partial pressure of oxygen exceeds about 1.4 atm. What happens to the amount of oxygen in a diver's bloodstream when he or she breathes oxygen at elevated pressures? How can this be reversed?

Step-by-Step Solution

Answer

Under elevated pressures, more oxygen dissolves in a diver's bloodstream, causing oxygen toxicity. It is reversed by reducing the partial pressure of oxygen, either by ascending to a shallower depth, breathing a gas mix with less oxygen, or using a hypobaric chamber.

Step 1: Understanding Oxygen Toxicity

Oxygen toxicity occurs when the partial pressure of oxygen in the lungs exceeds a safe threshold, typically around 1.4 atm, which can lead to increased levels of oxygen dissolved in the bloodstream. Increased pressure increases the amount of oxygen that can be dissolved in the blood, according to Henry's Law.

Step 2: The Effect of Elevated Pressures on Oxygen in Blood

When a diver breathes air at increased pressures, like when diving to considerable depths, the amount of oxygen the blood can hold increases. This is due to the increased pressure forcing more oxygen to dissolve into the bloodstream.

Step 3: Reversing Oxygen Toxicity

To reverse the effects of oxygen toxicity, the diver must decrease the partial pressure of oxygen. This can be done by ascending to a shallower depth where the pressure is lower, by breathing a gas mix with a lower percentage of oxygen, or by using a hypobaric chamber if available.

Key Concepts

Partial Pressure of Oxygen

Scuba divers are trained to pay close attention to the partial pressure of oxygen during their dives. The term 'partial pressure' refers to the portion of the total atmospheric pressure that is exerted specifically by the oxygen within the breathing gas mix. This pressure can be calculated using the formula \( P_{O2} = P_{total} \times F_{O2} \) where \( P_{O2} \) is the partial pressure of oxygen, \( P_{total} \) is the total ambient pressure, and \( F_{O2} \) is the fraction of oxygen in the gas mixture.

At increased depths, the ambient pressure rises, and so does the partial pressure of oxygen in the breathing gas. When a diver inhales at a depth where the ambient pressure is greater, the oxygen molecules are more compressed, hence more of them can enter the diver's lungs with each breath, leading to an elevated partial pressure of oxygen in the diver's bloodstream.

Henry's Law

The underlying scientific principle that explains how increased pressure leads to more dissolved oxygen in the bloodstream is known as Henry's Law. This law states that at a constant temperature, the amount of a given gas that will dissolve in a liquid is directly proportional to the partial pressure of that gas in contact with the liquid.

• The formula for Henry's Law is \( C = kP \) where \( C \) is the concentration of the dissolved gas, \( k \) is Henry's Law constant unique to each gas-liquid pair, and \( P \) is the partial pressure of the gas.
• Simply put, if you increase the pressure of a gas above a liquid, more of the gas will dissolve into the liquid until an equilibrium is reached.

In the context of diving, as the pressure increases with depth, more oxygen dissolves into the diver's blood per Henry's Law, and if the pressure becomes too high, it leads to oxygen toxicity.

Dissolved Oxygen in Bloodstream

The bloodstream's capacity to carry dissolved oxygen increases as the pressure surrounding the diver escalates. This might seem beneficial at first glance; however, there is a dangerous side to it. If too much oxygen dissolves into the bloodstream, a condition known as hyperoxia or oxygen toxicity can occur.

This condition entails a range of symptoms from benign concerns like a mild headache and fatigue, to serious complications such as seizures and lung damage. It's important for divers to understand their limits and monitor their exposure to high oxygen concentrations to prevent oxygen toxicity from occurring.

Reversing Oxygen Toxicity

If a diver encounters symptoms of oxygen toxicity, immediate action is crucial to reverse its effects and avoid serious health consequences. The primary method to counteract the elevated levels of oxygen in the blood is to reduce the overall partial pressure of the gas.

• One way is by ascending to a shallower depth. Since pressure decreases as one ascends towards the surface, the partial pressure of oxygen in the bloodstream will also be reduced correspondingly.
• Another way is to switch the breathing gas to one with a lower concentration of oxygen. Special gas mixtures like Nitrox with less oxygen than air can be used to reduce the oxygen levels a diver is exposed to.
• Lastly, using a hypobaric chamber, although not commonly accessible in diving scenarios, is a controlled environment where pressure levels can be carefully managed to treat oxygen toxicity.

These processes help in reducing the amount of oxygen dissolved in the blood, thereby averting the toxic effects.