Affiliations: Jackson, MS
Dr. Collop is Professor of Medicine, Division of Pulmonary and Critical Care Medicine, University of Mississippi Medical Center.
Correspondence to: Nancy A. Collop, MD, FCCP, Professor of Medicine, Division of Pulmonary and Critical Care Medicine, University of Mississippi Medical Center, 2500 N. State St, Jackson, MS 39216; e-mail: email@example.com
John Gray’s famous book, Men Are From Mars, Women
Are From Venus, focuses on the differences between men and
women.1 This book deals with relationships between men and
women using a metaphor that Martians (men) and Venusians
(women) met, fell in love, and developed loving relationships; on
moving to Earth, they forgot they were from different planets.
Subsequently, their relationships deteriorated. Maybe the sexes are
more different than we think, and maybe our understanding of disease
states will benefit from closer examinations of the variations of
specific diseases between the sexes.
In the context of Gray’s book, obstructive sleep apnea (OSA) is a
Martian’s disease. The reason for this is not completely understood.
The study in this issue of CHEST (see page 1442) by Mohensin
compares upper-airway size utilizing the acoustic reflectance technique
in a group of men and women referred to a university sleep center.
Similar studies2–3 utilizing other imaging techniques in
normal subjects have shown that although women have smaller pharynges
when seated, on recumbency the differences between men and women
disappear. The current study population, because they were a group of
patients at risk for OSA, were more obese than patients in prior
studies (mean body mass index [BMI] > 33
kg/m2). The authors showed that although the
women had higher BMIs and smaller pharynges than the men, they had less
severe OSA. Additionally, the size of the pharynx (< 3.2
cm2) correlated with the severity of OSA
only in men. This article suggests there is something
inherently different about the properties of the upper airway in men
compared to women.
Collapsibility of the upper airway depends on its size, the surrounding
muscle tone, and the characteristics of the tissue. All of these are
interrelated: if the muscles that surround and dilate the airway tone
are lax, the airway will narrow; if there is an increased amount of fat
in surrounding tissues, the airway may be compressed. Other studies
have investigated the gender differences related to muscle tone in the
upper airway.4–5 Upper-airway resistance increases with
sleep onset, and this results in a reduction in minute ventilation.
Awake genioglossus electromyelogram (EMG) activity in women may be
related to hormonal status (luteal vs follicular phase of the menstrual
cycle vs postmenopausal state), difference does not seem to affect
upper-airway resistance.4There appears to be no
significant difference in muscle tone in upper-airway dilators
(genioglossus and tensor veli palatini) between men and women during
sleep, although men have a higher upper-airway
resistance.5 Unfortunately, these studies were done in
normal subjects, so how this extrapolates to OSA patients is unclear.
Sex hormones have also been thought to influence the development of
OSA. A recent study by Bixler et al6showed that OSA was
much more prevalent in postmenopausal women who were not receiving
hormone replacement therapy (HRT), compared to postmenopausal women
receiving HRT or premenopausal women. HRT has also been shown to
decrease sleep-disordered breathing indexes (apnea/hypopnea index[
AHI]) in postmenopausal female patients.7Other
reports8–9 have shown that OSA is more prevalent in women
with androgen excess, for instance, polycystic ovary syndrome. New
onset of OSA developed in a woman who received exogenous
testosterone.9 This suggests testosterone may also play an
Other investigators have examined the surrounding tissue in the upper
airway. MRIs of the upper airway have shown differences between the
sexes; nonobese male subjects were shown to have more fat in their
necks compared to the rest of their bodies.10Another
study,11 looking specifically at physical examination
findings, showed that male patients with a narrowing of the lateral
pharyngeal walls and/or tonsil enlargement were at greater risk for
OSA, but no specific physical examination finding was predictive of OSA
in female subjects.
Polysomnography findings have also been shown to differ between men and
women with OSA. Not only do women have lower AHI results than men, most
of the difference in AHI between men and women occurs during nonrapid
eye movement (NREM) sleep. The AHI in patients during rapid eye
movement (REM) sleep is equal in men compared to women, suggesting that
whatever protects women from upper airway collapse in NREM sleep
disappears on entering REM sleep.12–13
Is there a common theme to explain the gender difference in OSA? The
size of the airway seems to make a difference in men, and this may be
an effect of a difference in muscle tone (lower in men) and tissue
characteristics (floppier in men). The difference in tone may be
abolished when REM sleep is entered, which would explain why the AHI
difference between men and women disappears in REM sleep.
Differences in tissue characteristics could not explain that change.
Clearly, further studies are needed to elaborate on the differences
between men and women. Identification of what protects women from more
severe OSA could potentially lead to new treatments. As stated in an
excerpt from Gray’s book1: “When you remember that men
are from Mars and women are from Venus, everything can be explained.”
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