Sighs during sleep in adult humans - Perez-Padilla et al. (1983)
Key Points
Sighs are natural and occur in most mammals
Sighs during sleep, however, are associated with lighter sleep periods and more arousals
Sighs during sleep are also associated with sleep apnea
The Breathing Diabetic Summary
We all sigh. It’s common in most mammals. But by definition, a sigh is a big breath, which something that we typically want to avoid. Moreover, excessive sighing is often observed in patients who suffer from panic disorder. However, when we sleep, our respiratory patterns change. They become more autonomic and less dependent on behavioral and environmental factors. Therefore, the authors of this paper wanted to know where sighs fit in during sleep. How often do they occur? Are they associated with a particular sleep stage? Are there any other changes that coincide with sighing during sleep? These are some of the questions they set out to answer.
They recruited 12 healthy subjects and monitored their sleep for two consecutive nights. All of the sleep data was recorded on the second night. They analyzed breaths occurring before and after sighs to determine associations with other breathing patterns and arousal. A sigh was defined as a breath 2X as big as the mean breathing volume during baseline recordings.
The results showed that sighs were fairly common during sleep, with an average of about 10 per subject. However, there was a large inter-subject variability, with some subjects only sighing once and others sighing 25 times per night.
They found that sighs occurred more during light sleep stages and that they were associated with increased arousal. Their data did could not distinguish if increased arousal caused sighs, or if sighs caused increased arousal. However, they speculate that increased arousal helps promote sighing.
Another interesting finding was that sighing was often followed by changes in respiratory patterns. For example, central apneas were closely related to sighs. A statistical analysis revealed that this association was much greater than just coincidence. Because sighs are big breaths that offload more CO2, the authors also found that sighs often were followed by hypoventilation (less breathing).
Overall, sighing is a natural breathing phenomenon. However, this paper found that sighing is associated with higher states of arousal and with sleep apneas. Thus, although we cannot monitor our own sighing during sleep, it might be useful to watch for excessive daytime sighing as a sign of increased anxiety or stimulation. Then, when we do notice it, we can practice Principle 1 to reset, relax, and restore our autonomic and respiratory balance.
Abstract from Paper
We analyzed sighs (breaths with a tidal volume at least twice that of baseline breaths) during sleep in 12 normal adults. We found a total of 124 sighs in the group, with an average of 1.66 sighs/h of sleep, but with great intersubject variation (range: 1-25 sighs/night). There were sighs in all sleep stages, but there were more per hour in stage 1. 64.4% of the sighs were associated with an increase in EMG activity or EEG frequency, starting either before or immediately after the sigh. The remainder of the sighs were not associated with any arousal or sleep stage changes. The normal variability of heart rate with breathing is exaggerated during sighs, probably because of the greater inflation and the associated arousal. Sighs have larger mean inspiratory flows (Vt/Ti), expiratory flows (Vt/Te), and a larger fraction of respiratory cycle spent in inspiration (Ti/Ttot) than the previous breaths, all evidence of a change in respiratory control. Sighs during sleep may occasionally be followed by central apneas, hypoventilation, or considerable slowing of respiratory rate. Although it has been shown that a sigh renders the respiratory centers refractory to another sigh, we found that sighs sometimes occur in pairs.
Journal Reference:
Perez-Padilla R, West P, Kryger MH, (1983) Sighs during sleep in adult humans, Sleep, 6(3), 234 – 243.