When breathing a gas mixture at depth, how does the effect of the gas compare to that at the surface?

When breathing a gas mixture at depth, the effect of the gas is greater than at the surface due to the increased pressure exerted by the surrounding water. As the diver descends, the pressure increases, which affects how gases behave in the body. According to Dalton's Law, the partial pressure of each gas in a mixture is what drives the exchange of gases in the lungs and tissues.

At depth, the partial pressures of the gases the diver breathes are higher compared to when breathing at the surface. This can lead to a greater concentration of the gases in the diver's tissues as well, which is a critical consideration when planning dives and managing the risks associated with nitrogen absorption (e.g., decompression sickness) and potential toxicity of other gases like oxygen or helium.

In essence, while the same gas mixture is being breathed, its behavior and the physiological effects it produces manifest differently under increased pressure, resulting in a more significant effect compared to that experienced on the surface.