Sleep apnoea
“Ageing may lead to reduced muscle tone and hence greater likelihood of airway collapse”
in severely obese South Asians compared to obese white Europeans. South Asians also had more severe OSA compared to BMI-matched white Europeans.” There is an increased risk of OSA as one
gets older. Ageing may lead to reduced muscle tone and hence greater likelihood of airway collapse. NHS Choices states that: “Although OSA can occur at any age, it is more common in people who are over 40.” By contrast, obesity is a significant
Go = Gonion, Gn = Gnathion. H = Hyoid, T = Tubercle Fig 4
Continued »
Journal of Applied Physiology in April ı997 concluded: “The results support the anatomic hypothesis that sleep apneic subjects have a structurally narrowed and collapsible pharynx.” Studies have also found that the more
inferior the hyoid bone, the more likely the tongue will be displaced lower and potentially increase the risk of developing OSA (Fig 4).
OSA and soft tissues Typically, someone with OSA will have a disproportionately higher volume of soft tissue compared to their hard tissue cage and any inflammation of these soft tissues may contribute to airway obstruction. Whether increased fat pads also predispose to airway compression is disputed. Nocturnal rostral distribution,
whereby fluid is displaced from the legs to the neck during sleep, can lead to increased pressure in the blood vessels, hence the sort of upper airway collapse seen in patients with, for example, heart failure.
OSA and general factors Here, I shall discuss how gender, ethnicity, age and obesity can contribute to the pathophysiology of OSA. OSA is present in twice as many men
(around 4 per cent of the population) as women (2 per cent). Incidentally, these figures are only for those diagnosed with OSA – probably only one fifth of all those who have the disease. It appears men are more likely to
experience airway collapse because of their higher pharyngeal resistance, but the effect of testosterone may also be a factor. Women’s risk of having sleep apnoea increases after menopause, and those who have the condition have more severe symptoms than do younger women. Although there has only been limited
research, there are ethnic differences in the prevalence and severity of OSA. For instance, epidemiological studies show African-Americans have a larger tongue and longer soft palate, whereas Asians generally have a shorter maxilla and mandible and lower BMI than Caucasians. A study by Wen Bun Leong et al
published in the Journal of Clinical Sleep Medicine (Vol 09, No. 09) concluded: “OSA prevalence and comorbidities was greater
factor in the development of OSA. This may be due to the increased fat deposits in the neck resulting in greater extraluminal pressure and airway narrowing. Certainly, it has been shown that fat deposition around the neck is more critical than body mass, which is why neck circumference is such an important measure. NHS Choices states: “Men with a collar size greater than around 43cm (ı7 inches) have an increased risk of developing OSA.” Other general factors that may
contribute to the pathophysiology of OSA include high blood pressure, diabetes, genetics, smoking, alcohol and drugs (hypnotics and sedatives).
So far, so interesting Before I move on from the physiology to the pathology, I’ll summarise what we’ve learned so far. For factors contributing to the
pathophysiology of obstructive sleep apnoea, I invariably use the table in an article by Deegan and McNicholas published in European Respiratory Journal in ı995. Incidentally, I recommend this article Pathophysiology of obstructive sleep apnoea, because it goes into much greater depth than I have room for here. It is available at
http://erj.ersjournals.com/ content/8/7/ıı6ı General factors are anthropometric
(male sex, age, obesity), drugs (ethanol, hyponotics) and genetics. Reduced upper airway calibre can be a result of specific anatomical lesions
Continued » Ireland’s Dental magazine 41
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