PADI Divemaster Certification Practice Exam

What factor influences a tissue compartment’s rate of gas absorption and release?

1. Ambient temperature

2. Halftime

3. Depth duration

4. Experience level of the diver

The correct answer is: Halftime

The rate at which a tissue compartment absorbs and releases gas is primarily influenced by the halftime of that compartment. Halftime refers to the period it takes for a tissue compartment to reach half of its maximum saturation during gas absorption, or to release half of the absorbed gas during off-gassing. Different tissues in the body have varying halftimes based on their vascularity, density, and metabolic activity. For instance, highly vascular tissues such as the brain or heart have shorter halftimes, allowing them to absorb and release gases quickly, while less vascular tissues like fat have longer halftimes. Understanding the concept of halftime is crucial in dive planning and in managing decompression because it helps predict how quickly a diver will off-gas nitrogen after ascent. Consequently, a diver must gradually ascend and may need to perform safety stops to allow these compartments sufficient time to safely release gases without risking decompression sickness. Ambient temperature, depth duration, and experience level of the diver can influence dive characteristics and safety, but they do not fundamentally determine the biological mechanism of how gases are absorbed or released within tissue compartments. Thus, halftime is the key factor in understanding the kinetics of gas exchange in diving physiology.