Sighs Shape Respiratory Variability and Pupil Dynamics and Adapt to Sustained Attention Demands

Sighs are spontaneous deep breaths thought to play a homeostatic role in respiratory control. Their relationship to respiratory variability has been repeatedly demonstrated. How sighs are related to task engagement, performance, structure and arousal has remained unclear. Presently, we investigated sigh behavior across two sustained attention tasks using respiratory belt recordings. Participants completed either a Gradual Contrast Change Detection task (dataset Grad) or a Paced Auditory Cue Entrainment task (dataset PACE), with subgroups performing the latter under spontaneous (NIB) or slow-paced (IB) breathing conditions. Sighs were identified as breaths at least twice the mean inspiratory volume (Vi). We analysed the total variability (coefficient of variation; CV) and structured variability (lag-1 autocorrelation; AR) of respiratory rate (RR) and Vi, their changes over the task, and around sigh events. In spontaneous breathing groups (Grad, NIB), sigh frequency was positively related to CV in both RR and Vi suggesting a relationship to overall variability, and negatively correlated to RR-AR, suggesting a relationship to the structure of the variability. Sigh frequency and CV increased over the task duration, while post-sigh dynamics showed decreased CV and increased Vi-AR, supporting sighs role in resetting the temporal structure. In IB group, sigh frequency was drastically reduced and no pre-post sigh changes were observed. Sighs were also associated with changes in pupil diameter, implicating involvement of the noradrenaline-mediated arousal system. Sighs were not related to any alterations in task performance or subjective engagement. Finally, stronger respiratory phase-locking to task timing was associated with higher sigh frequency and increased respiratory variability, suggesting that sigh behavior could be influenced by task dynamics. The lack of task performance differences should be clarified using demanding tasks which could draw out variability. These findings support a role of sighs with respect to respiratory variability, phase-locking behavior and pupil-linked arousal during prolonged cognitive tasks.