Sleep Disorders Medicine is a clinical specialty which is concerned with the diagnosis and treatment of patients with disorders of sleep and daytime alertness. The spectrum of disorders is extremely broad, from primary dysfunction's of the neural mechanisms of sleep and arousal (e.g., narcolepsy), to sleep exacerbated medical conditions (e.g., chronic obstructive pulmonary disease), to disturbances associated with medical, psychiatric or behavioral syndromes. Despite the multidisciplinary origin of the field, there is the crucial commonality of the fundamental processes and disorders of the sleeping brain. Whereas many medical specialties deal primarily with disorders of the specific organ system, sleep disorders medicine is concerned with the phenomenon of sleep and its abnormalities, disorders of alertness, and the effects of normal sleep processes upon other medical disorders.

Evolution of Sleep Disorders Medicine
The field of sleep disorders medicine has evolved from a core body of basic scientific knowledge for the most part obtained since the mid 1950's. Particularly important was the recognition that the brain and, consequently, other organ systems show unique, active physiological processes during sleep. Sleep is not simple the absence of waking existence, but involves specialized neural activity serving an as yet unidentified vital function. Further, rapid eye movement (REM) and non-REM sleep were identified as two separate neural states, each of which is physiologically distinct from wakefulness. It has become clear that these neural states result in physiological processes which is place many humans at increased medical risk during sleep. Additionally, a variety of pathological deviations of normal sleep physiology have also been identified. Thus, the normal physiology of sleep and sleep-related disturbances is recognized as a factor in morbidity and mortality. A clinical specialty of sleep disorders medicine developed because this specialized knowledge of the sleeping brain provides information necessary for the prevention, diagnosis and treatment of these disorders.

The development and rapid growth of the field occurred despite the initial absence of formal educational programs within traditional medical education (e.g. residencies, training fellowships, medical school curricula). The concern over standards of practice and the need for professional education led to the establishment of the American Sleep Disorders Association. This organization is active in professional education and the development of standards and guidelines for patient care.

The Role of Polysomnography
Polysomnography, the physiological assessment of the sleeping patient, developed with the recognition that examination of the waking patient may fail to uncover serious disorders which are evident during sleep. Polysomnographic studies not only improve our ability to assess patient but are largely responsible for the exponential increase in knowledge of clinical issues since about 1960. They provided the first insights into the nature of narcolepsy by documenting sleep-onset REM periods. The first glimpses into the complexity of insomnia were obtained when vigorous insomnia complaints were occasionally accompanied by polysomnographic evidence of continuous, apparently normal sleep. Polysomnographic studies of sedative/hypnotic medications provided an objective assessment of hypnotic efficacy and uncovered the alterations in sleep stage architecture produced by such compounds.

Since 1970, the alarming frequency with which the sleeping brains fails to adequately regulate breathing, as in sleep apnea syndromes and a variety of other conditions accompanied by sleep-related hypoventilation, has been documented. Insights into the neural mechanisms of psychopathologies, particularly affective disorders, have been obtained from the polysomnographic documentation of REM sleep alterations. The quantification of daytime alertness via the multiple sleep latency test has aided in the differential diagnosis of the somnolent patient and may be a yardstick for understanding sleep quality and quantity. Finally, the advances in the descriptions and delineation of the various sleep-related illnesses obtained via polysomnography and skilled clinical practice resulted in the development and publication of an initial psychology of sleep disorders in 1979 and the International Classification of Sleep Disorders in 1990.

Impact of Sleep Disorders
We have long known that disorders of sleep are common. More recently, formal epidemiological studies have demonstrated that over twenty-five percent of adults have occasional or frequent complaints about sleep and that drugs are prescribed and used in connection with sleep more than for any other therapeutic purpose. Moreover, sleep problems appear to be associated with mortality risk. It is well documented that more people die in the early morning hours than at any other time of day, presumably with some association to sleep. Further, there is a strong correlation between morbidity and mortality rates and how long an individual reports sleeping each night, with both of these increasing significantly at the extremes of four and ten hours. Although the nature of these relationships is as yet unclear, disturbances of sleep and alertness, in some way, impact upon survival.

In addition to influencing mortality, sleep disorders have an enormous impact upon quality of life. Millions of individuals live much of their lives in a fog of unrelenting sleepiness and fatigue. The medical, economic and social toll of sleep disorders is staggering, from the thousand of tired industrial shift workers who work when the brain is timed to sleep, to the accident victim who lost his fight to remain alert at the wheel, to the elderly grandfather placed in a nursing home because of nighttime wandering, to the sleepy child who once again fails the fifth grade, to the grieving parents who have lost their sleeping child to sudden infant death syndrome. Sleep disorders medicine is concerned with these and all individuals affected by any perturbation of sleep and alertness.

Practitioners of sleep disorders medicine recognize the need for early diagnosis and treatment of sleep-related illnesses throughout the entire life span. They also see a need to develop and disseminate preventative strategies. However, all of these objectives require basic research. Only then will our knowledge about sleep and its disorders progress toward the goal of improved sleep and a more vital, energetic waking existence for future generations.