Relationships between inspiration and expiration times, Tin and Tex, and inter-breath interval (BB) were analyzed in a database composed by 120 young healthy volunteers undergoing a session divided in different stages aimed to induce relax and emotional stress, where respiration was recorded with a chest band. Tin and Tex were represented as a function of BB so that two regression lines were obtained. The slopes of both regression lines, αTin and αTex, as well as the angle formed by them, θ, were used to characterize respiratory dynamics during each stage. Moreover, mean respiratory frequency in each stage was calculated. Statistical significant differences (p < 0.001) were obtained when comparing relax and stress stages, with increased αTex and θ, and reduced αTin during stress. Also differences between distinct stress stages were found. Results suggest that inspiration and expiration patterns, and hence respiratory dynamics, are different under stress, so its analysis could be useful for stress assessment.