Effects of N2O narcosis on breathing and effort sensations during exercise and inspiratory resistive loading

• Published in: Journal of applied physiology (1985) Vol. 81; no. 4; pp. 1562 - 1571
• Main Authors: Fothergill, D. M, Carlson, N. A
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.10.1996; American Physiological Society
• Subjects: Adult; Air Pressure; Airway Resistance - drug effects; Airway Resistance - physiology; Anaerobiosis - physiology; Anesthetics, Inhalation - pharmacology; Applied physiology; Biological and medical sciences; Diving; Exercise - physiology; Exercise Test; Heart Rate - physiology; Human physiology applied to population studies and life conditions. Human ecophysiology; Humans; Inert Gas Narcosis - physiopathology; Male; Medical sciences; Nitrous Oxide - pharmacology; Respiratory Function Tests; Respiratory Mechanics - drug effects; Respiratory Mechanics - physiology; Transports. Aerospace. Diving. Altitude; Physical exercise; Human; Inspiration; Bicycle ergometer; Effort; Tolerance; Environmental factor; Resistance; Narcosis; Sensorial perception; Diving; Nitrogen protoxide; Respiration; Military
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.1996.81.4.1562

D. M. Fothergill and N. A. Carlson Naval Medical Research Institute, Bethesda, Maryland 20889-5607 Received 28 December 1995; accepted in final form 3 June 1996. Fothergill, D. M., and N. A. Carlson. Effects of N 2 O narcosis on breathing and effort sensations during exercise and inspiratory resistive loading. J. Appl. Physiol. 81(4): 1562-1571, 1996. The influence of nitrous oxide (N 2 O) narcosis on the responses 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% N 2 O gas mixture and a nonnarcotic gas of the same P O 2 , 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 cmH 2 O · 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-ratio scale. The level of narcosis was rated between slight and moderate for the N 2 O 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 N 2 O 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 breathing (15%; P  < 0.001) when the subjects breathed the N 2 O 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% N 2 O are not of 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 N 2 O narcosis. nitrous oxide; respiratory sensation; perceived leg exertion; nitrous oxide narcosis; diving; exercise tolerance; breathing resistance