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Emotions and breathing have historically been associated in both animal and human studies. More recent research has shown that a number of respiratory characteristics (speed of breathing, depth, etc.) can vary based on emotional experience. The sigh (a distinct deep breath) is a specific form of respiratory action that is expressed during both positive and negative emotional states, such as those of contentment and frustration, respectively. However, the motivations for sighing have only recently come under examination, and little research has been conducted on the physiological and psychological aspects of the action.
Published online in Physiology & Behavior, the described experiment included 34 participants (17 female). They first completed a survey designed to measure trait anxiety, and were then fitted with electrodes and other equipment necessary to track respiration and physiological measures of anxiety/relaxation (skin conductivity, muscle tension, CO2 concentration).
Each subject took part in three different session blocks. No breathing instructions were given in the first block, while the following two included either deep breath (sighing) prompts or breath holding (not sighing) instructions. Instances of spontaneous sighing were also recorded for the instructed sigh group. Relief was self-reported continuously throughout all trials.
Statistical analyses of biological and psychological measures revealed two significant effects of sighing. Reported relief increased in the five seconds following sighs, but not after breath holding or without instructions. Muscle tension decreased moderately in the post-sigh measurement period, signifying a reduction in anxiety and/or increased relaxation.