Clinical reviewEthnicity and obstructive sleep apnoea
Introduction
Obstructive sleep apnoea (OSA) is a disorder characterized by repetitive episodes of complete or partial upper airway obstruction during sleep, often associated with hypoxemia, increased breathing effort and arousals. OSA has a range of deleterious consequences that include unrefreshing sleep and excessive daytime sleepiness, neurocognitive impairment, and cardiovascular morbidity.1, 2, 3, 4, 5, 6, 7 OSA has been increasingly recognized over many years as an important health issue with major clinical and public health implications.8, 9 The clinical syndrome is typically referred to as OSAS (OSA plus daytime sleepiness) or more recently modified to OSAHS, where H introduces hypopnoea into the acronym.10
The most commonly quoted estimate of prevalence of OSAS derives from a study of middle-aged public servants from Wisconsin, USA: 4% in males, 2% in females.11 The ethnicity of the Wisconsin Sleep Cohort was overwhelmingly Caucasian. This prevalence gives an indication of the minimal size of the health problem associated with sleep apnoea. Documented risk factors for OSA include increasing age, male gender, obesity, craniofacial structure, ventilatory control dysfunction, and there is also some evidence for other risk factors including alcohol and other drugs, and both active and passive smoking. Ethnicity is also suggested as an important associated indicator of OSA risk and/or severity.12, 13, 14, 15, 16 The major purpose of this review will be to consider the ethnic aspects of obstructive sleep apnoea.
Section snippets
Ethnicity and health
The definition of ethnicity or of an ethnic group in medical literature is not always clear, but would generally pertain to a group of individuals sharing a common racial and/or cultural background.17 A very broad connotation of race separates just three categories, i.e. African, Caucasian and Mongoloid (sic), but this limited classification can be criticised on numerous grounds. Mixing of the human genetic pool has long occurred in developed countries, and in previously colonized regions of
Adult prevalence
Previously published reviews of OSA epidemiology have largely described prevalences from studies in predominantly Caucasian populations. A 1996 review20 included 12 prevalence studies, which varied considerably in the methods used, particularly systematic use or not of polysomnography (PSG) as the arbiter of OSA, the definitional criteria for OSA, geographical location and gender inclusiveness. Estimated whole population prevalences varied between 0.3 and 15%, although the authors went on to
Ethnicity as an OSA risk factor
Genetics, culture, environment (incorporating socioeconomic status) and development may all influence separately or in various combinations some of the recognized OSA risk factors. In addition, these components to a greater or lesser degree inform the construct of ethnicity which itself has been identified as a separate OSA risk factor. This complex amalgam of influences makes analysis of the contribution of ethnicity to OSA problematic (Fig. 1).
Craniofacial structure and upper airway
Craniofacial structure has both a bony component and a soft tissue component. The former would be expressed in adults in the relatively fixed elements of the skull, facial bones and cervical spinal skeleton, which in concert provide the bony framework and support of the upper airway. Those fixed elements can be identified on lateral cephalograms and are usually expressed as indicative angles and linear distances, and two-dimensional areas. It is then possible to establish norms for those bony
Phenotypic interactions
The racial variations in the prevalence and expression of these phenotypes may be related to ethnic differences in risks for obesity, craniofacial morphology and ventilatory control. Directly, these factors which are to some extent heritable, in various combinations and modulated by cultural and environmental influence, will determine the overall susceptibility for collapse of the upper airways.69 The interaction of these factors with each other may also serve to modify the contribution
Acknowledgements
The authors are grateful for the assistance provided by Dr Louis Wong during the initial draft of the paper. We would also like to thank Maria Vanessa V Alvarez for her invaluable help in the creation of the graphics used for the cephalometric figures.
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