Effects of N2O narcosis on breathing and effort sensations during exercise and inspiratory resistive loading.
D M Fothergill, N A Carlson
Journal of Applied Physiology October 1996 DOI: 10.1152/jappl.1996.81.4.1562 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Experimental crossover study Peer reviewed |
|---|---|
| Sample size | 13 |
| Population | Male US Navy divers |
| Intervention | inspiratory resistive loading |
| Dose | 23% N2O |
| Measures | category-ration scale for respiratory effort, leg exertion, and narcosis; time to exhaustion; heart rate; inspiratory occlusion pressure; esophageal pressure; expired minute ventilation |
| Key findings | Breathing 23% nitrous oxide did not significantly change time to exhaustion or perceived leg exertion compared with a nonnarcotic gas, and it reduced respiratory effort ratings by 25% during steady-state and incremental exercise. The authors conclude that N2O-induced changes in ventilation, heart rate, and respiratory effort are not large enough to influence exercise tolerance at surface pressure, and that load-compensating respiratory reflexes are not depressed by N2O narcosis. |
Abstract
The influence of nitrous oxide (N2O) narcosis on the response to exercise and inspiratory resistive loading was studied in thirteen male US Navy divers. Each diver performed an incremental bicycle exercise test at 1 ATA to volitional exhaustion while breathing a 23% N2O gas mixture and a nonnarcotic gas of the same PO2, density and viscosity. The same gas mixtures were used during four subsequent 30-min steady-state submaximal exercise trials in which the subjects breathed the mixtures both with and without an inspiratory resistance (5.5 vs. 1.1 cmH2O.s.l-1 at 1 l/s). Throughout each test, subjective ratings of respiratory effort (RE), leg exertion, and narcosis were obtained with a category-ration scale. The level of narcosis was rated between slight and moderate for the N2O mixture but showed great individual variation. Perceived leg exertion and the time to exhaustion were not significantly different with the two breathing mixtures. Heart rate was unaffected by the gas mixture and inspiratory resistance at rest and during steady-state exercise but was significantly lower with the N2O mixture during incremental exercise (P < 0.05). Despite significant increases in inspiratory occlusion pressure (13%; P < 0.05), esophageal pressure (12%; P < 0.001), expired minute ventilation (4%; P < 0.01), and the work rate of N2O mixture, RE during both steady-state and incremental exercise was 25% lower with the narcotic gas than with the nonnarcotic mixture (P < 0.05). We conclude that the narcotic-mediated changes in ventilation, heart rate, and RE induced by 23% N2o are not sufficient magnitude to influence exercise tolerance at surface pressure. Furthermore, the load-compensating respiratory reflexes responsible for maintaining ventilation during resistive breathing are not depressed by N2O narcosis.