The Sigh and Meaning of Sighing: Dysregulation of Breathing
Definition of sighs (how to define sighing)
Sighing is defined as an involuntary inhalation (inspiration) that is 1.5-2 times greater than the usual tidal volume. Some studies suggest that a sigh should be defined as 1.5 times increase in the personal typical tidal volume (Leiner & Abramowitz, 1958). Some other authors suggested another definition of a sigh: it should be at least as twice as deep as the person's average inhalation (Wilhelm et al, 2001; Caughey et al, 1943).
Respiratory mechanics of sighs
Sighing is usually done using primarily the upper chest, dorsal muscles, or upper sternum (Lum, 1975; Gallavardin, 1925; Leiner & Abramowitz, 1958) and is a sign of chest or thoracic breathing (Katagiri et al, 1998; Lum, 1975; Lum, 1981; Gallavardin, 1925; Leiner & Abramowitz, 1958).
Sighs during sleep
Sighing can be present during sleep in normal adults (Perez-Padilla et al, 1983) and infants (Gerard et al, 2002). This study on sighs during sleep in adults (Perez-Padilla et al, 1983) discovered that all 12 normal adults had sighs during their night sleep, from 1 to 25 sighs per night.
To Sigh means inhaling a lot and reduced brain O2
After analyzing hundreds of sighs in more than 80 people with mostly respiratory problems* (see the note below), Leiner & Abramowitz (1958) found that in more than 80% of people the volume of air for one sigh was more than 1,300 ml and in some people up to 2.5-3 liters, with an average of about 1,700 ml per sigh for this group. These authors also discovered that, for the majority of subjects (more than 82%), the amount of air for one sigh was ranging from 40% to 60% of their vital capacity (the difference between the maximum inhalation and maximum exhalation).
This produces a similar effect on brain O2 content as light hyperventilation.
The normal vital capacity in healthy people is 4,500 ml which indicates that this group of subjects had reduced vital capacity (due to presence of respiratory problems). Hence, this study suggests that the average sighing volume in normal adults (with no lung pathologies) is over 2,000 ml. The normal tidal volume is 500 ml. This suggests that a typical adult's sigh is 4 times larger, a lot more, than the normal tidal volume.
Meaning of sighs: health problems
Sighing is generally regarded as a symptom of abnormal or dysregulated breathing since normal breathing in healthy subjects is regular or periodic (i.e., without sighing). Excessive or frequent sighing is considered a sign of panic disorder (Abelson et al, 2001; Schwartz et al, 1996; Wilhelm et al, 2001a; Wilhelm et al, 2001b), anxiety states (Lum, 1981), low back pain (Chaitow, 2004), nervous disturbance (Rechnitzer et al, 1929), dyspnea (Magarian et al, 1983), neurocirculatory asthenia (cardiovascular disease), and nervous instability in young women (White & Hahn, 1929), and respiratory neurosis (Christie, 1935). Some studies point that people with depression often suffer from excessive sighing. In comparison with normal and healthy subjects, sighing is more common in patients with rheumatoid arthritis who have depression (Robbins et al, 2011). Hence, in most cases, frequent or excessive sighing means being under stress.
However, sometimes excessive sighing and/or yawning can take place due to resetting of the respiratory center (e.g., after the meal is digested, after or even during physical exercise, and so forth). In such cases, one should hold the breath after their usual exhalation (perform the body-oxygen test) and do Buteyko reduced breathing exercise with air hunger for 1-2 minutes to stop sighing and increase brain oxygenation.
Respiratory causes of frequent sighs
While many causes of sighing have been suggested, the most impressive evidence relates to the link between sighing and typical symptoms of hyperventilation (Aljadeff et al, 1993; Brashear, 1983; Okel BB & Hurst, 1961; Saltzman et al, 1963). Many other researchers consider sighing as a hallmark and classical symptom - or form - of hyperventilation (Bass & Gardner, 1985; Berczeller, 1993; Brashear, 1983; Fraser & Pare, 1979; Gliebe PA & Auerback, 1944; Howell, 1990; Ker, 1937; Lum, 1975; Lum, 1981; Magarian et al, 1983; Rice et al, 1950).
Blashear (1983) in his article in Lung titled "Hyperventilation Syndrome" suggested that physicians should regard occasional sighing as a subtle clue to presence of hyperventilation syndrome. Hence, decades of clinical research suggest that hyperventilation is the cause of sighing.
Some researchers revealed that the sigh rate was higher during conditions of relief compared to conditions of stress (Vlemincx et al, 2009), while later, in another study, they found that sighing could be triggered by both mental load and recovery from the attention task (Vlemincx et al, 2011). Sighs can be an expression of an activity, intention or desire that has to be discarded (Teigen, et al, 2008).
When infants are not swaddled, they have increased frequency of sighs during sleep (Gerard et al, 2002). This is probably due to the fact that swaddling restricts ventilation, prevents chest breathing, increases arterial CO2 and cellular O2 concentrations, and makes breathing more regular.
Sighing is sometimes thought to be caused by a spasm of the diaphragm (Gallavardin, 1925; Katagiri et al, 1998; Leiner & Abramowitz, 1958). Indeed, chest breathing means poor diaphragm function with insufficient stimulation of lung tissue and stretch receptors located in the lower parts of the lungs. Therefore, sighing can provide some relief or solution to these problems. However, these problems are the natural effects of hyperventilation.
Hyperventilation leads to alveolar hypocapnia and reduced oxygenation of the diaphragm. Furthermore, arterial hypocapnia (CO2 deficiency in the arterial blood) leads to spasms in all muscles of the human body, including the diaphragm (see CO2 links below).
Hence, various causes of hyperventilation, such as supine sleep, mouth breathing, stress, anxiety, overeating, overheating, and poor posture, can intensify sighing. It makes sense then that sighing is often accompanied by other symptoms of hyperventilation, such as dyspnea (shortness of breath), breathlessness (heavy and deep breathing), yawning, and coughing. These observations also support the idea about the key role of overbreathing in the pathophysiology of sighing. Therefore, excessive or frequent sighing means that a person is hyperventilating.
Overwhelming majority of modern people are hyperventilators and chest breathers (see links below). Therefore, most modern studies cannot shed more light on the root causes of sighing since these studies investigate people who already suffer from overbreathing.
Effects of occasional sighs
Even several very deep and fast breaths cannot improve oxygenation of the arterial blood (which is equal to 98-99% for tiny normal breathing). The main effect of frequent or excessive sighing is hypocapnia (lack of CO2) in the lungs, arterial blood and body cells. Many authors suggest that markedly reduced arterial-CO2 tension could be maintained with very little effort with only an occasional sigh superimposed on the normal breathing pattern (Brashear, 1983; Okel BB & Hurst, 1961; Saltzman et al, 1963). Hence, even occasional sighing means chronic hyperventilation and a reduced oxygen level in cells, while frequent or excessive sighing produces devastating effects on the main gases (CO2 and O2) in the brain, heart and other vital organs.
Many people with dyspnea (breathlessness) testify that sighing brings some relief to their respiratory muscles. This relief may relate to the mechanical effects of sighing on the diaphragm and other respiratory muscles. Several studies have found that artificial sighs, during mechanical ventilation of various lung patients, have positive effects on oxygenation of their arterial blood and diminished viscoelastic impedance.
Treatment of sighs: increase body O2
You can discover which criteria helps to get rid of problems with sighing for good. I tested this on hundreds of my students. These details are provided as your bonus content below.
* The main health problems in this study of sighs (Leiner & Abramowitz, 1958) were tuberculosis, tuberculosis pleurisy, emphysema, bronchogenic carcinoma, sarcoidosis, hemoptysis, asthma, bronchiectasis, arteriosclerotic heart disease, rheumatic heart disease, and cor pulmonale.
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