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Polysomnography is defined succinctly if a bit vaguely in Stedman's Medical Dictionary as the "simultaneous and continuous recordingof normal and abnormal physiological activity during sleep." Most sleep specialists consider it the key laboratory study for the diagnosis of sleep apnea and other sleep-related breathing disorders.Furthermore, many would consider the electroencephalogram or EEG--a record from scalp electrodes of the electrical activity of the brain--as a key measure of "physiological activity" in describing sleep patterns, and therefore as important as the measurement by various means of breathing itself and its results (i.e., blood oxygen saturation) in defining sleep apnea. We should be aware that the EEG dates back only to Berger's first recordings in 1929.
Berger noted changing patterns of EEG activity with changing levels of consciousness, from wakefulness to sleep. Recording of the EEG with other physiological measures, especially eye movements, enabled Dement and Kleitman in 1957 to define different stages of sleep, particularly the recurrent cycling throughout the night of Rapid Eye Movement (REM) sleep, associated with the waking pattern of the EEG but no return of consciouness or responsiveness to the outside environment.
But clinical research doesn't always require complex technology. In the earliest stages of discovery, just describing a disease well from a clinical standpoint is an important step. Almost a hundred years before Berger, Charles Dickens wrote a vivid description on what later became identified as a stereotypical, severe form of sleep apnea in a character called "Fat Joe" from The Pickwick Papers.
"Fat Joe" had such excessive daytime sleepiness that he fell asleep standing up, while in the process of knocking on a door! Thereafter, "Fat Joe" was referred to in clinical descriptions later in the 19th century of other hypersomnolent, obese patients with loud snoring, which came to be called the "Pickwickian Syndrome" in reference to Dickens' novel. Around this time, a case was reported with successful treatment by weight reduction. Later, the term "Pickwickian Syndrome" became supplanted by Obstructive Sleep Apnea, which includes a wider range of less severe cases without the daytime cardiorespiratory impairment of the Pickwickian syndrome.
The current understanding of Obstructive Sleep Apnea depended critically on the recording of EEG and respiratory movements during sleep. But as recently as the 1960's, sleep apnea was still considered a "rather rare and bizarre disease," without any widely accepted neurological aspects. One of the obstacles at that time was difficulty in analyzing and representing the enormous amount of data contained in the EEG. As newer techniques made this possible, it became possible to describe different stages of sleep in terms of the spectrum of waveforms in the EEG, leading to an understanding of EEG "arousal" responses caused by respiratory events during sleep. These events were characterized by periodic decreases in breathing, complete cessation of breathing, rises in blood carbon dioxide and falls in blood oxygen levels.
In 1969, the demonstration that tracheostomy could benefit sleep apnea led to the understanding of this disease as due to an obstruction of the airway above the level of the chest. But this first case later showed return of some symptoms. The phenomenon of central apneas--without any obstruction--was discovered and labelled, for a time, as "Ondine's curse," was considered to be related to reduced sensitivity of brain receptors to carbon dioxide. The connection between daytime fatigue and difficulty breathing during sleep due to muscular disease like polio came to be recognized as another of the the various sleep-related breathing disorders that include, as probably the most common, obstructive sleep apnea.
This article was written by a researcher who first became involved with sleep and sleep apnea over thirty years ago. It is quite understandable--but perhaps not easily accessible--to the lay reader. The author writes about fellow sleep researchers in the manner of one who observed many of the most important developments in sleep apnea research as they took place. His account helps to put in perspective the relationship between the different diagnostic terms that have arisen and may cause some confusion even now, such as the Pickwickian Syndrome. When my own sleep doctor quite recently reviewed results of my first pulmonary tests and noted my elevated blood carbon dioxide level as a consequence of my sleep apnea, I asked: "Do you mean I have Pickwickian Syndrome?" He answered no, that I wasn't that bad. Clearly, I had failed to understand what it meant that this expression required "extreme obesity, hypoventilation, and general debility," as defined in Stedman's dictionary.
Finally, Dr. Kuhl's narrative helped me to understand more clearly the temporal sequence of events that up to now I appreciated only dimly: the evolving clinical description of sleep apnea in the 19th century, they key steps of recording EEG and respiratory movements during sleep in the late 1920's, and the considerable interval of 40 years with these tools that it took for a detailed description of sleep stages to emerge for the connection of respiratory events to arousals to become understood.
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