PADI Divemaster Certification Practice Exam

What characteristic do "fast" tissues in a Haldanean model have compared to "slow" tissues?

1. Lower M-values

2. Higher M-values

3. Equal M-values

4. Variable M-values

The correct answer is: Higher M-values

In the context of the Haldanean model, "fast" tissues are characterized by having higher M-values compared to "slow" tissues. M-values, or maximum allowable inert gas pressures, are essentially measures of how much inert gas (like nitrogen) a tissue can hold at a given pressure before experiencing adverse effects, such as decompression sickness. Fast tissues, such as the brain and the skeletal muscles, have a high blood supply and a greater affinity for inert gases, allowing them to absorb and eliminate these gases more quickly during changes in pressure. This means they reach saturation faster when diving and can also release the absorbed gas more rapidly upon ascension. Conversely, slow tissues, such as fat, have lower blood flow and less capacity for gas absorption, which results in lower M-values. This differential behavior highlights the varying rates of gas exchange between the different types of tissues in the body, which is crucial for understanding decompression strategies and the management of dive profiles. This aspect of the Haldanean model is fundamental for divers, as it influences how they plan their dives and consider safe ascent rates to avoid decompression illness. Understanding these dynamics helps in mitigating the risks associated with diving depths and durations.