Background: Nitrous oxide (N2O) is commonly administered in conjunction with parturition, which requires the performance of repeated high-force voluntary muscle actions. Therefore, we examined the effect of a subanesthetic dose of N2O on the force-velocity relationship of the quadriceps femoris muscle.
Methods: Nine healthy subjects performed maximal voluntary muscle actions once while breathing air and once while breathing a normoxic gas mixture containing 35% (N2O). Peak torque of the knee extensors was measured during concentric muscle contractions at different angular velocities (30, 60, 90, 150 and 210 degrees s-1), and eccentric (30, 60, 90, and 150 degrees s-1) and isometric (knee-joint angle approximately equal to 60 degrees) muscle actions. Maximal angular velocity was determined during unloaded knee extensions.
Results: N2O decreased peak torque at any given angular velocity. The overall decrease in peak averaged 4.8 +/- 2.2% (P < 0.0001). Likewise, N2O decreased maximal angular velocity by 5.7 +/- 4.3% (P < 0.01). Thus, the impairment in muscle function induced by a 35% N2O is only minute and hence most likely of little significance in clinical practice.