Effect of subanaesthetic concentrations of nitrous oxide on the regulation of ventilation in man.

The pattern of ventilation was studied in eight healthy male volunteers breathing, in sequence, air and then two subanaesthetic concentrations of nitrous oxide (20% and 40%). The effect of these gas mixtures on the response to an added inspiratory resistance (3.88 kPa litre-1s-1) was examined. During unrestricted breathing of 40% nitrous oxide, there was a significant decrease (P less than 0.05) in inspiratory time (TI), a concomitant increase in the rate of ventilation and a significant decrease (P less than 0.05) in the end-tidal carbon dioxide tension (PE'CO2) compared with air breathing. For the first breath on load while breathing 40% nitrous oxide, there were significant decreases (P less than 0.05) in the responses for TI and tidal volume (VT) compared with the responses when breathing air. TI, VT, minute volume and PE'CO2 were similar for each gas mixture during steady state breathing against resistance. The increase in PE'CO2 when breathing 40% nitrous oxide against the resistance represented a significant (P less than 0.01) difference in response to the load compared with that breathing air. There was no significant change in these variables when breathing 20% nitrous oxide.