Question

If a person were to dive with scuba equipment to a depth of 66 feet, which of these statements would be false? a. The arterial \(\mathrm{P}_{\mathrm{O}_{2}}\) would be three times normal. b. The oxygen content of plasma would be three times normal. c. The oxygen content of whole blood would be three times normal. d. All of the above measurements would remain the same as at sea level.

Short answer

The false statement is: "All of the above measurements would remain the same as at sea level." While the arterial \(\mathrm{P}_{\mathrm{O}_{2}}\) does increase with depth, the oxygen content of plasma and whole blood does not increase threefold.

Step-by-step solution

Understand the effect of increased pressure on a scuba diver at depth

When a scuba diver descends to a depth of 66 feet underwater, the pressure increases. This increased pressure largely affects the amount of dissolved gases in the blood and tissues of the diver, particularly oxygen.

Analyze the given statements

Now, let's take a look at each statement to see which one turns out to be false: a. The arterial \(\mathrm{P}_{\mathrm{O}_{2}}\) would be three times normal. b. The oxygen content of plasma would be three times normal. c. The oxygen content of whole blood would be three times normal. d. All of the above measurements would remain the same as at sea level.

Applying Henry's Law to the arterial \(\mathrm{P}_{\mathrm{O}_{2}}\)

Henry's Law states that the amount of dissolved gas is directly proportional to the partial pressure of that gas in the gaseous mixture and the solubility of that gas in the liquid. When the pressure increases, the amount of dissolved oxygen in the blood (arterial \(\mathrm{P}_{\mathrm{O}_{2}}\)) would also increase. As a result, Statement a seems to be true.

Analyze the claim about oxygen content of plasma and whole blood

The oxygen content of both plasma and whole blood is mainly determined by two factors: the oxygen saturation of hemoglobin and the dissolved oxygen in plasma. When a diver goes deeper, the additional oxygen that dissolves in plasma due to increased pressure is relatively small compared to the amount of oxygen bound to hemoglobin. Thus, the oxygen content of plasma (Statement b) and whole blood (Statement c) doesn't increase threefold. As a result, both Statements b and c are false.

Address the possibility of all measurements remaining the same

Lastly, Statement d claims that all measurements remain the same as at sea level. However, we have already established that arterial \(\mathrm{P}_{\mathrm{O}_{2}}\) does increase with depth and statements b and c are false. Hence, Statement d is also false. Our conclusion is that the false statement is: "All of the above measurements would remain the same as at sea level." because the arterial \(\mathrm{P}_{\mathrm{O}_{2}}\) does in fact increase, but the oxygen content of plasma and whole blood would not be three times normal.

Key concepts

Henry's Law

Understanding Henry's Law is crucial when considering the effects of diving on the body. Simply put, Henry's Law states that the concentration of a dissolved gas in a liquid is directly proportional to the partial pressure of that gas above the liquid. For scuba divers, this translates to a higher amount of gases being dissolved in the bloodstream as they dive deeper because the pressure increases underwater.One real-world application of Henry's Law is the use of hyperbaric oxygen therapy, where patients are placed in a high-pressure environment to increase the amount of oxygen that can be absorbed into the blood. This principle also serves as a warning for divers, as it underlies the risk of decompression sickness, often known as 'the bends', which can occur if the diver ascends too quickly and gas bubbles form in the tissues.

Arterial PO2

The term arterial PO2 refers to the partial pressure of oxygen in the arterial blood. It's a measure of how much oxygen is available to be transported to tissues throughout the body. Normally, arterial PO2 is tightly regulated by the respiratory system to ensure organs receive sufficient oxygen.However, during scuba diving, due to the increased pressure underwater, according to Henry's Law, the arterial PO2 will increase. This condition can be beneficial to a point, improving the oxygenation of tissues, but it can also pose risks, such as oxygen toxicity if the PO2 becomes too high. It's essential for divers to monitor their depth and the time spent at high-pressure environments to manage the risks associated with changes in arterial PO2.

Oxygen Content in Blood

Oxygen content in blood is determined by the hemoglobin-bound oxygen and the dissolved oxygen in the plasma. The majority of oxygen in the blood is carried by hemoglobin, a protein in red blood cells, with a small percentage dissolved in the plasma. When discussing the oxygen content of blood while scuba diving, we must understand that while arterial PO2 increases, the overall oxygen content doesn't drastically change because the hemoglobin saturation curve plateaus at high oxygen pressures—most of the hemoglobin is already fully saturated at normal atmospheric pressure.With the increase in depth during a dive, dissolved oxygen in plasma does go up slightly, but since this is such a small fraction of total blood oxygen, it doesn't significantly affect the overall oxygen content. This is a key point for divers and medical professionals to recognize when considering oxygen delivery and the risk for oxygen toxicity.

Effects of Pressure on Dissolved Gases

The effects of pressure on dissolved gases in the body play an essential role in scuba diving. As a diver descends, the water pressure increases, and consequently, according to Henry's Law, more gas dissolves into the diver's bodily fluids. This increased solubility affects all gases, including nitrogen, which doesn't have a significant metabolic role like oxygen does. Nitrogen build-up can lead to decompression sickness unless managed appropriately through controlled ascent and decompression stops.It's also important to note the role of pressure on the function of natural bodily gases, such as those in the lungs and sinuses. Divers need to constantly equalize the pressure in these air-filled spaces to avoid discomfort or injury. Understanding and respecting the effects of pressure on dissolved gases is integral to safe and enjoyable scuba diving experiences.