Spontaneous breathing was measured in healthy persons scoring either high (N=45) or low (N=30) on trait negative affectivity (NA), during a 10 min period of quiet sitting using the LifeShirt System®. Sighing and respiratory variability before and after sighs were assessed. Total respiratory variability of minute ventilation was indexed by the coefficient of variation and structured (correlated) variability was quantified by the autocorrelation. Total variability was higher before a sigh than before a non-sigh, without concomitant differences in structured variability, suggesting more random variability before a sigh. After a sigh, correlated variability increased whereas it remained the same after a non-sigh. Thus sighing acted as a resetter of the respiratory system. However, when comparing the low and the high NA group, this pattern was specific for high NA individuals. We conclude that it is important to take into account individual difference variables when studying the psychophysiological functions of sighing.

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From a dynamic systems perspective, healthy breathing is characterized by complex variability. However, slow regular breathing instructions are often included in relaxation techniques. This study investigates the influence of relaxation training on natural breathing dynamics. Spontaneous breathing was measured in healthy persons during 5 sessions of relaxation training without breathing instructions (N = 29) vs. during quiet sitting resembling spontaneous relaxation (N = 29). Each session started with 10 minutes baseline recordings and ended with a mental stressor and a recovery phase. Results showed no differences between conditions in subjective relaxation and mean respiratory parameters. However, structured breath-to-breath variability increased across sessions during baseline and stress in the relaxation group only. In the control group, total variability increased across sessions during stress without concomitant changes in structured variability. The results point to the importance of respiratory variability in breathing regulation and suggest integration of a dynamic systems perspective in relaxation research.