Combined effects of mild hypothermia and nitrous-oxide-induced narcosis on manual and cognitive performance
M. Moes, Antonis Elia, Mikael Gennser, M. Keramidas
American Journal of Physiology. Regulatory, Integrative and Comparative Physiology January 8, 2024 DOI: 10.1152/ajpregu.00246.2023 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Within-subject, single-blinded experimental study Peer reviewed |
|---|---|
| Sample size | 14 |
| Population | Adult men |
| Dose | 30% N2O |
| Duration | Two ~12-h sessions, each with three 120-min cold water immersions separated by 120-min rewarming; sessions separated by at least 4 days |
| Measures | finger dexterity test, Spaceflight Cognitive Assessment Tool for Windows (WinSCAT) |
| Key findings | Mild hypothermia alone impaired short-term memory (about 37%) and learning (about 18%) only in the first cold-water immersion, whereas inhaling 30% nitrous oxide reduced short-term memory (about 37%) and learning (about 35%) across all immersions and also impaired finger dexterity, attention, concentration, working memory, and spatial processing. The authors conclude that inert gas narcosis persistently aggravates cognitive function during prolonged cold exposure. |
Abstract
Divers are at enhanced risk of suffering from acute cognitive deterioration because of the low ambient temperatures and the narcotic action of inert gases inspired at high pressures. Yet, the behavioral effects of cold and inert gas narcosis have commonly been assessed in isolation and during short-term provocations. We therefore evaluated the interactive influence of mild hypothermia and narcosis engendered by a subanesthetic dose of nitrous oxide (N2O; a normobaric intervention analog of hyperbaric nitrogen) on cognitive function during prolonged iterative exposure. Fourteen men partook in two ∼12-h sessions (separated by ≥4 days), wherein they performed sequentially three 120-min cold (20°C) water immersions (CWIs), while inhaling, in a single-blinded manner, either normal air or a normoxic gas mixture containing 30% N2O. CWIs were separated by a 120-min rewarming in room-air breathing conditions. Before the first CWI and during each CWI, subjects performed a finger dexterity test, and the Spaceflight Cognitive Assessment Tool for Windows (WinSCAT) test assessing aspects of attention, memory, learning, and visuospatial ability. Rectal and skin temperatures were, on average, reduced by ∼1.2 °C and ∼8 °C, respectively (P < 0.001). Cooling per se impaired (P ≤ 0.01) only short-term memory (∼37%) and learning (∼18%); the impairments were limited to the first CWI. N2O also attenuated (P ≤ 0.02) short-term memory (∼37%) and learning (∼35%), but the reductions occurred in all CWIs. Furthermore, N2O invariably compromised finger dexterity, attention, concentration, working memory, and spatial processing (P < 0.05). The present results demonstrate that inert gas narcosis aggravates, in a persistent manner, basic and higher-order cognitive abilities during protracted cold exposure.