Effect of Subanaesthetic Concentrations of Nitrous Oxide on the Regulation of Ventilation in Man

Abstract

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.

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

“…The small but significant increase in V E and concomitant reduction in PET CO 2 under N 2 O narcosis found in the present study has also been reported by others (8,37,39). In anesthetized cats, the increase in V E has been attributed to stimulation of the pulmonary stretch receptors by N 2 O (41).…”

“…This supports the findings of other investigators (39,42) who have found that the load-compensating respiratory reflexes important in maintaining ventilation during inspiratory resistive loading are not impaired by breathing mixtures containing up to 50% N 2 O. Moreover, in a recent study (13) in which the effects of 20% N 2 O on the ventilatory responses to hypercapnia were studied in five subjects, it was concluded that this subanesthetic concentration of N 2 O did not affect the peripheral chemoreflex loop.…”