INTRODUCTION IN THE DECADES FOLLOWING THE FIRST CLINICAL DESCRIPTIONS OF ABNORMALITIES OF BREATHING DURING SLEEP,1-3 medical specialists

IN THE DECADES FOLLOWING THE FIRST CLINICAL DESCRIPTIONS OF ABNORMALITIES OF BREATHING DURING SLEEP,1-3 medical specialists became progressively more concerned about these disorders. The most widely studied sleep breathing disorders include: obstructive sleep apnea syndrome, central sleep apnea syndrome, Cheyne-Stokes breathing syndrome and sleep hypoventilation syndrome.4 The upper-airway resistance syndrome, (UARS) results from cyclical increases in upper-airway resistance leading to brief arousals and daytime sleepiness.5 Whether UARS is a distinct syndrome or a variant of OSAS has been a matter of debate.6,7 When obesity leads to hypoventilation, the term obesity-hypoventilation syndrome or the Pickwick Syndrome is often used. Sleep-disordered breathing or sleep-related breathing disorder are terms commonly used to describe all these disorders. Obstructive sleep apnea syndrome (OSAS), the most common of this group of disorders, is a condition in which there are repeated episodes of upper-airway obstruction during sleep. The physiologic mechanisms that terminate the obstruction lead to sleep fragmentation. The nocturnal symptoms of this syndrome include snoring and apneas witnessed by the bed partner. The main daytime symptom is excessive sleepiness.8 OSAS has been the most widely studied sleep breathing disorder, and it is the only one for which there exists a body of epidemiologic data. This report will therefore focus on OSAS, but will mention UARS where published data warrants inclusion. OSAS may have several important effects on public health. It has been suggested that sleep breathing disorders are associated with many common health problems such as arterial hypertension,9-13 ischemic heart disease,10,12,14 cardiac arrhythmias,12 and stroke.12,13 OSAS is also associated with a poor quality of life and poor work or school performance.15,16 The early epidemiological studies of OSAS included only men until 1993, when Young et al. for first time included women in a large study of prevalence of OSAS in a general population sample.17 (Table 1) The likely reason for women being omitted from epidemiological studies was because reports from clinics in the 1970s and 1980s suggested that OSAS was primarily a disease of males and review articles from that era stated that the male:female ratio for the disorder varied from 60:1 to 10:1.18 More recent studies on general populations have reported a male:female prevalence ratio only of about 2:1 to 3:1. The reason for the now demonstrated higher prevalence of OSAS in females has not been widely investigated. One hypothesis that has been put forth is the possibility that women have different manifestations from men and are missed on this basis leading to a gender bias.19 Another documented unintentional possible bias is that some researchers may study mainly males in diseases that affect both genders.20,21 For example, even some recent epidemiologic studies of OSAS had only male subjects,22,23 and an CPAP compliance report only included male subjects.24 In some reports this may be due to the study being done at an institution that deals primarily with males (e.g., hospitals that treat military veterans).24 Another unintended bias facing female patients is related to the criteria used by agencies approving use of CPAP treatment. For example, the major government funder in the USA required an apnea index of 30 for CPAP treatment reimbursement. In some series (see below section "PSG findings") the average female with OSAS had an apnea index of less than 30 and therefore would have been denied treatment. In April 2002 new guidelines for reimbursement approved treatment if apnea hypopnea index was between greater than 15 or if AHI were greater than 5 in the presence of sleepiness, impaired cognition, mood disorders or insomnia, or documented cardiovascular disease (http://www.hcfa.gov/coverage/8b3-bbb2.htm; accessed April 5, 2002). This now made bias based on gender less likely. We will address the influence of gender in sleep-disordered breathing. First, we will review gender differences in the clinical