Gender differences in age and BMI distributions in partial upper airway obstruction during sleep
Introduction
The obstructive sleep apnea–hypopnea syndrome is a common condition that affects both men and women. Men have a higher prevalence of sleep apnea than women, with male to female ratios of approximately 2 or 3:1 in community based samples (Young et al., 1993, Redline et al., 1994, Bixler et al., 2001). However, women are symptomatic with lower apnea–hypopnea index (AHI) than men (Young et al., 1993). This finding suggests that other factors, not identified with conventional polygrafic sleep studies, are likely to contribute to the symptoms. While periodic obstruction of the upper airway (episodes of apnea and hypopnea) is well recognized in patients with upper airway obstruction during sleep, nonperiodic obstruction (prolonged episodes of partial upper airway obstruction or obstructive hypoventilation, Schwab et al., 2005) has been largely neglected in scientific studies as “simple snoring”. However, breathing against partially obstructed upper airway may increase the intrathoracic pressure variation more than tenfold, cause significant respiratory workload and excessive sleepiness (Pelin et al., 2003). The esophageal catheter is the reference method for detection but no studies have been accomplished with this methodology to assess the occurrence of partial upper airway obstruction in larger patient populations. The static-charge-sensitive bed (SCSB) is a noninvasive alternative to detect prolonged non-apneic episodes of grossly increased (20 cmH2O or more) intrathoracic pressure variations (Polo et al., 1991, Polo, 1992, Kirjavainen et al., 1996) without the discomfort of an esophageal catheter.
We have previously shown that healthy postmenopausal women have a high incidence of partial upper airway obstruction during sleep (Polo-Kantola et al., 2003), accounting half of all observed breathing abnormalities in women compared to only third in men (Anttalainen et al., 2007). Partial obstruction, even in the absence of episodes of apnea, may cause clinically significant symptoms. Patients with symptomatic partial upper airway obstruction respond and adhere to nasal continuous positive airway pressure (CPAP) therapy at least as well as those with “conventional” obstructive sleep apnea syndrome (Anttalainen et al., 2007). Therefore, partial upper airway obstruction cannot be considered just as a mild form of sleep-disordered breathing (SDB) with less symptoms or low AHI, which is associated with poor adherence to CPAP therapy (Engleman et al., 1999, Rosenthal et al., 2000). Because of underrecognition of partial upper airway obstruction during sleep, it is possible that also SDB is underdiagnosed in females (Young, 2001).
Respiratory instability predisposes to periodic upper airway obstruction whereas stable breathing underlies partial obstruction. At menopause women undergo hormonal changes which could have stabilizing effect on control of breathing, whereas increasing obesity could predispose patients to respiratory instability because of increasing sympathetic activity and carotid body gain. Our hypotheses are the following: (1) Aging predisposes women more than men for nonperiodic partial upper airway obstruction during sleep. (2) Periodic upper airway obstruction is more common in men with increasing obesity. We retrospectively analyzed nocturnal respiratory recordings in 233 age and BMI-matched male–female pairs with special interest in the incidence of periodic upper airway obstruction (apnea and hypopnea) and nonperiodic partial obstruction measured noninvasively with the SCSB.
Section snippets
Subjects
Using our pulmonary clinic sleep database for diagnostic sleep studies between the years 1994–1998, we identified 304 male-female pairs matched for BMI (±2 kg/m2) and age (±3 years). The complete data for the purpose of the present study were found in 233 pairs. The menopausal state of the women was determined through hospital records (ovarian surgery or medical history) or questionnaires (self reported last menstruation period more than one year prior the sleep study), or based on age at the
Results
The age and BMI association of the various breathing patterns, measured as percentage of TIB, are presented in 3D format in Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6. The significances of these non-linear associations tested as odds ratios in four age and BMI categories are presented in Table 1 (women) and Table 2 (men). The odds ratios of normal weight (BMI < 25 kg/m2) patients or patients under 45 years equalled 1.
Discussion
Breathing pattern during sleep is influenced by the central respiratory command and the stability of the upper airway. High respiratory drive associates with low levels of partial pressure of carbon dioxide (), unstable upper airway and periodic breathing, which is typical for patients with the obstructive sleep apnea syndrome. Patients with lower respiratory drive (for instance snoring postmenopausal women) are more likely to tolerate higher , allowing better stability of the upper
Acknowledgements
This work was supported by grants from Turku University Central Hospital (EVO grant), The Finnish Anti-Tuberculosis Association Foundation, Finnish Sleep Research Society, and The Väinö and Laina Kivi Foundation. Olli Polo was supported by Tampere Tuberculosis Foundation.
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