A sigh following sustained attention and mental stress: effects on respiratory variability.

Normal breathing consists of considerable correlated variability (parameters of subsequent breaths are correlated) and some random variability. Emotional and attentive states alter normal breathing variability, which can be restored by a sigh. The present study aimed to investigate the effects of mental arithmetic and sustained attention on respiratory variability. In addition, the effect of a spontaneous sigh following both conditions was examined, compared to an instructed sigh and a control maneuver. Mental arithmetic and sustained attention were characterized by decreased correlated and total breathing variability, respectively. A spontaneous sigh restored correlated variability. An instructed sigh restored correlated variability following mental arithmetic, and increased total variability following sustained attention. These results suggest that a spontaneous sigh and an instructed sigh, when physiologically appropriate, restore respiratory variability influenced by stress or attention.