Link to full free article:
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1806-37132007000100017&tlng=en&lng=en&nrm=iso

Physiopathology of obstructive sleep apnea-hypopnea syndrome
Martins AB, Tufik S, Moura SM.
Sleep Medicine, Federal University of São Paulo, São Paulo, SP, Brazil.

"The physiopathology of obstructive sleep apnea syndrome is multifactorial. Gender and obesity status, as well as genetic, anatomic, and hormonal factors, together with ventilatory drive, interact in a diverse manner in the physiopathology and clinical expression of the disease. Obesity is the main risk factor, since increases in body mass index, visceral fat, and neck circumference are strong predictors of the disease. Progesterone increases the activity of the upper airway dilator muscles and therefore plays a protective role in premenopausal women. This explains the fact that the prevalence of the disease is higher in postmenopausal patients, in patients with polycystic ovary syndrome, as well as in males. Evidence supports the fact that, as individuals grow older, there is a decrease in muscle tonus, with a consequent reduction in the dimensions of the upper airway lumen. Craniofacial anomalies, such as in retrognathia or micrognathia, are accompanied by posterior positioning of the tongue and can result in narrowing of the upper airway lumen. Finally, decreased ventilatory drive has been detected in patients with obstructive sleep apnea syndrome and hypercapnia."

PMID: 17568874 [PubMed - in process]

The following is quoted from the article:

Age
It is believed that with aging the activity of the upper airway musculature is decreased.

Gender
Prevalence is higher in men than in women. Women present greater genioglossus muscle tone, which can be
considered a defense mechanism designed to maintain upper airway permeability.

Hormones
Estrogen and progesterone promote the maintenance of upper airway permeability (by improving muscle
tone), as well as increasing respiratory drive. The androgens induce greater fat deposition and relaxation of
the pharyngeal dilator muscles. Polycystic ovary syndrome is characterized by a higher level of circulating
androgens and, therefore, a higher risk of sleep apnea. Menopause also increases the chances of sleep
apnea.

Anatomical factors
Micrognathia and hypoplasia of the mandible are associated with the posterior positioning of the base of the
tongue and with upper airway narrowing. Thickening of the lateral pharyngeal walls also cause upper airway
narrowing.

Genetic factors
Some risk factors, such as craniofacial structure, distribution of body fat, neural control of the upper airways
and central respiratory command, can be inherited.

Posture and gravity
The dorsal decubitus position promotes the posterior positioning of the tongue and soft palate, thereby
reducing the area of the oropharynx.

Body fat
High body mass index. Central or visceral obesity is quite important. Predisposing factors: abdominal circumference
> 94 cm in men and > 80 cm in women; neck circumference > 40 cm.

Other causes
Acromegaly, Down’s syndrome, hypothyroidism, genetic syndromes and deposition diseases (amyloidosis and
mucopolysaccharidosis) can promote the narrowing of the upper airways, which is a predisposing factor for
sleep apnea.



Last edited by Guest MJ on Thu Mar 13, 2008 8:29 pm; edited 2 times in total

Link to full article: http://ajrccm.atsjournals.org/cgi/content/full/172/11/1363

Pathogenesis of obstructive and central sleep apnea.
Am J Respir Crit Care Med. 2005 Dec 1;172(11):1363-70. Epub 2005 Aug 11.
David P. White
Division of Sleep Medicine, Harvard Medical School and Brigham and Women's Hospital, Boston, Massachusetts

Brigham and Women's Hospital Division of Sleep Medicine, Sleep Research at BI, 75 Francis Street, Boston, MA 02115, USA.

Considerable progress has been made over the last several decades in our understanding of the pathophysiology of both central and obstructive sleep apnea.

Central sleep apnea, in its various forms, is generally the product of an unstable ventilatory control system (high loop gain) with increased controller gain (high hypercapnic responsiveness) generally being the cause. High plant gain can contribute under certain circumstances (hypercapnic patients).

On the other hand, obstructive sleep apnea can develop as the result of a variety of physiologic characteristics. The combinations of these may vary considerably between patients. Most obstructive apnea patients have an anatomically small upper airway with augmented pharyngeal dilator muscle activation maintaining airway patency awake, but not asleep. However, individual variability in several phenotypic characteristics may ultimately determine who develops apnea and how severe the apnea will be. These include: (1) upper airway anatomy, (2) the ability of upper airway dilator muscles to respond to rising intrapharyngeal negative pressure and increasing Co(2) during sleep, (3) arousal threshold in response to respiratory stimulation, and (4) loop gain (ventilatory control instability). As a result, patients may respond to different therapeutic approaches based on the predominant abnormality leading to the sleep-disordered breathing.

PMID: 16100008 [PubMed - indexed for MEDLINE]