The investigators will study whether nefopam modulates the counterirritation of laboratory induced dyspnea in healthy subjects. The effect of nefopam on experimental dyspnea will be measured with a visual analog scale (VAS) and a validated multidimensional dyspnea profile (MDP). The effect of treatment on counterirritation will be measured by recording LEP obtained using a CO2 laser system. The amplitude of the N2-P2 component of the LEP is the main study outcome.