narcosis: one construct, many systems

In pharmacology, narcosis is a reversible, dose-dependent depression of the central nervous system (drowsiness, loss of coordination, and ultimately unconsciousness) produced by agents whose potency tracks their solubility in lipid rather than any shared chemical structure. Meyer's 1899 Zur Theorie der Alkoholnarkose, alongside Overton's parallel work, established this lipid-solubility correlation, and Franks and Lieb's 1994 Molecular and cellular mechanisms of general anaesthesia later refined the account toward specific membrane proteins while preserving the partition relationship. The referent is the graded anaesthetic state itself, indexed by the concentration or partial pressure needed to abolish a response, the same physical construct that, under pressure, turns an inert diving gas narcotic.[1][2]

Unit

The agent concentration or partial pressure producing a given depth of CNS depression

Recovery means

The state reverses as the agent washes out of nervous tissue and partitions back out of the membrane

Measured by

Indexed by potency measures such as the minimum alveolar concentration and by lipid-solubility (oil/gas partition) correlations

In diving physiology, inert gas narcosis (classically nitrogen narcosis, or "rapture of the deep") is the same anaesthetic depression produced when a normally inert breathing gas is inhaled at raised partial pressure during descent, impairing judgement, coordination, and consciousness as depth increases. Behnke, Thomson, and Motley's 1935 The psychologic effects from breathing air at 4 atmospheres pressure first pinned the effect on nitrogen's partial pressure, and Bennett and Elliott's physiology and medicine of diving sets out how its severity scales with depth and gas choice. It is not a separate disease but the ordinary narcosis construct realised underwater, which is why its intensity follows the lipid-solubility of the gas breathed, exactly as an anaesthetic does.[3][4]

Unit

The depth or inert-gas partial pressure at which measurable impairment appears

Recovery means

Symptoms clear rapidly on ascent as the inert-gas partial pressure falls

Measured by

Assessed by cognitive and performance testing against depth, and predicted from each gas's lipid solubility