Science for the Tec Diver: Narked with Meyer-Overton

Simple version: If you dive deep, you will get narked.

Slightly more sophisticated version: Nitrogen and oxygen act as narcotic agents; if you dive with air as a breathing gas, you will start to feel a certain amount of mental incapacitation below 30 meters. This will affect your vision, short-term memory and mood; It’s relatively quickly reversible when ascending to shallower depths.

Tec diver version: The narcotic strength of a gas is described by the Meyer-Overton correlation. This correlation, found in the early 20^th century by a German and a British physician, says that the more soluble a gas is in lipids, the stronger it acts as a general anesthetic. Here is a plot of this correlation:

from Wikipedia

Stare at the plot of the Meyer-Overton correlation for a while, my friend! Understanding this relationship is one of those fundamental insights which increases your understanding of the world by a significant amount, right away the very moment you get it.

The anesthetics used in surgery, such as isoflourane and halothane, are to the very right of this correlation: They dissolve very easily in lipids, and knock you out even in small amounts. Nitrogen lives on the top right corner of the Meyer-Overton correlation; it’s not very lipid-soluble and hence not very narcotic at atmospheric pressure. But that’s not the pressure we breathe it at when we dive. We all know that for every 10 meters you dive deeper, you gain 1 atmosphere in pressure. Hence, at depth you breathe nitrogen under higher pressure, and more nitrogen will dissolve in your tissues, including your brain.

This causes all the aforementioned neurological symptoms of “being narked”: the problems with memory, perception and mood.

Solubility alone is not the Solution

The fact that anesthetic power correlates with solubility of the anesthetics in lipids initially let scientists believe that the process of the anesthetics dissolving in the nerve membranes causes the anesthetic action. We no longer believe that the story is so simple.

The membrane of a nerve cell is not some amorphous liquid with the membrane proteins swimming around independently. Research in recent decades has shown that there is a significant amount of organization in how membrane proteins are arranged. Possibly this organization is distorted; certainly individual membrane proteins are affected, not just the membrane lipids. The latter effect has been shown for a number of ion channel proteins found in nerve membranes.

Interestingly, in contrary to the commonly held opinion, narcosis does not disappear right away when diving shallower or when surfacing. That fact, in my opinion, also speaks against a simple lipid dissolution mechanism of nitrogen narcosis.

History of the Meyer-Overton Correlation 

On a historical note, Hans Horst Meyer, after whom the Meyer-Overton correlation was jointly named, was a professor at my alma mater, the University of Vienna. When the national socialists took over Austria and its universities after the “Anschluss” in 1939, this highly accomplished scientist was ostracized by the opportunists who were swept into positions of power by the changing times. These days, he is honored by a bronze bust in the celebratory hall of the university.

Tec dive with us at Salaya Beach Houses! Let’s explore the deep reefs of Apo Island and the Dauin coast together!