Restless Nights: Understanding Snoring and Sleep Apneaby Peretz Lavie
People with severe sleep apnea may struggle for breath all through the night, not breathing for as long as ninety seconds at a time during their sleep. This syndrome, which affects at least four percent of men and two percent of women, can cause daytime fatigue, traffic and work accidents, deteriorating cognitive abilities, and cardiovascular problems. Yet until
People with severe sleep apnea may struggle for breath all through the night, not breathing for as long as ninety seconds at a time during their sleep. This syndrome, which affects at least four percent of men and two percent of women, can cause daytime fatigue, traffic and work accidents, deteriorating cognitive abilities, and cardiovascular problems. Yet until now there has been no accessible discussion of the history, physiology, and risk factors of sleep apnea. In this book Peretz Lavie, an expert in sleep research, tells the complete story of sleep apnea for the first time.
The book provides:
• an explanation of the symptoms of sleep apnea, including the most important one, snoring;
• an up-to-date description of the risk factors;
• a clear explanation why sleep apnea causes cardiovascular problems;
• a discussion of children’s breathing disorders in sleep;
• advice on how to get a consultation and diagnosis;
• evaluations of the treatments currently available;
• practical recommendations on how to live with the syndrome;
• interviews with the key figures in sleep apnea research;
• and more.
- Yale University Press
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Restless NightsUnderstanding Snoring and Sleep Apnea
By PERETZ LAVIE
Yale University PressCopyright © 2003 Yale University
All right reserved.
Chapter OneThe Breath of Life
Then the Lord God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul. -Genesis 2:7
Why did the author of the Book of Genesis make a point of stating that God brought the first man to life by breathing into his nose? We also breathe through our mouths, after all, and the volume of air inhaled through the mouth would appear to be greater than that inhaled through the nose. Part of the answer is that the ancients believed that breathing through the nose was more vital to existence than breathing through the mouth. "The matter of life depends on the breath of the nose, for hot air is expelled from the heart through the nose, and air enters through it to cool the heart," the twelfth-century scholar Abraham ben Meir Ibn Ezra claimed, and many other biblical commentators agreed.
These writers were greatly influenced by ancient Greek teachings regarding the role of breathing and the significance of the nose. Air's importance to life had been well known since the dawn of history. Hippocrates, the father of Greek medicine, wrote that the body needs three elements: food, drink, and air, with the last being the most important. The ancients were convinced that the reason air entered the lungs through breathing was to cool the heart, which was perceived to be the seat of life, for the heart was the only organ whose function could not be stopped without resulting in the cessation of life. According to the Greeks, the heart was the site of constant combustion, and the heat thereby produced was essential to all the body's organs, as well as to life itself. In the absence of cooling by means of breathing, the heart would be consumed. Galen (129-200 C.E.), who succeeded Hippocrates as "the prince of Greek medicine," wrote in his treatise on the purpose of organs: "I have shown that breathing is vital to the heart of living things, which must be cooled due to the heat of its combustion. Inhaling air cools it by providing the coolness of the air, whereas exhaling cools it by expelling the heat of combustion." According to Galen, breathing through the nose was preferable because it filtered dust particles and other impurities from the air, and even slightly warmed it. (Galen did not elaborate on the contradiction between the air's function in cooling the heart and the necessity of warming the air before it entered the lungs.)
The Greeks maintained that air had two additional functions: to assist in removing waste materials produced in the heart's combustion, and as a necessary ingredient in the creation of "vital spirits." These were formed in the left ventricle of the heart and flowed to all parts of the body, participating in each of its processes. Galen postulated that arteries carried blood to the heart's right ventricle, from which the blood passed to the left ventricle through hypothetical openings in the septum separating the two parts of the heart, and that only a small amount of blood reached the lungs. In the left ventricle, the blood mixed with air to create the "vital spirits."
Although the first person to cut his hand noticed that blood flowed from the wound, Galen's categorical assertion that blood passes from the heart's right ventricle to its left delayed any progress in understanding the circulation of blood for almost fourteen hundred years. In these long centuries of rigid religious conformity, attempts to investigate Galen's claims were perceived as heresy against established teachings and were severely punished by the Catholic Church. And any knowledge of the role of breathing in the existence of life had to wait for the discovery of the circulatory system and the development of chemistry.
The first to challenge Galen's theories was Michael Servetus (Miguel Serveto), a Spanish jurist, theologian, and physician. Servetus rejected the entire Galenic theory regarding perforations in the heart septum. He maintained that blood flowed from the heart to the lungs and then returned from there to the heart. Servetus, however, was also experimenting with unorthodox religious ideas, and he soon fell afoul of both the Catholic Church and John Calvin; he was burned at the stake for heresy in 1553. Progress in gaining any true understanding of the circulatory system was delayed roughly another half century, until William Harvey was finally able to refute the Galenic model.
Harvey, an Englishman, had studied medicine at Padua University in Italy with Hieronymus Fabricius, who investigated the vein valves that regulate the direction of the flow of blood. After his university studies, Harvey returned to England and established a flourishing medical clinic, which did not prevent him from continuing his research into the heart and its functions by means of surgery on a variety of animals. He used mathematical calculations to help him design carefully structured experiments, which proved undeniably that the blood flowing from the heart through arteries was the same blood that flowed back through the veins. Harvey announced his discovery of the circulation of blood in a lecture he gave at a London medical college in 1616. Regarding Galen's imagined openings in the septum and the heart's production of "vital spirits," Harvey declared, "Confound it, I can find no perforations in the septum of the heart, and I can see no way of proving their existence." Harvey's historic book De Motu Cordis (On the movement of the heart) was published in 1628, and in it he cited Galen no fewer than twenty-nine times, along with Aristotle, Hippocrates, and many others, although he was oblivious of the theories of Servetus.
Harvey's book sparked a controversy that lasted for more than a quarter century. Physicians, philosophers, natural science researchers, and all who considered themselves conversant with anatomy and physiology joined the debate. Even the general public rose to denounce the "heretic." Feeling against Harvey ran so high that he lost most of the patients under his care, and there were fears for his personal safety. In spite of the tumult surrounding him, Harvey did not respond to his detractors but patiently waited for the world to recognize the existence of the circulatory system, confident in his belief that the truth would eventually prove him right. And so it did. He was only fifty when his book was published, and he lived to be eighty, by which time he was able to enjoy the sweet taste of victory. Rene Descartes, the renowned French philosopher, was among the first to support Harvey's arguments regarding blood circulation, and one after another his opponents were compelled to admit that no other alternative was possible.
One link was missing from Harvey's model of the circulatory system-how is the cycle completed? How does blood flow from the arterioles to the smallest veins? Intervention by a microscopist was called for. Marcello Malpighi was born near Bologna, Italy, in 1628, the year Harvey published his book. Malpighi, who studied the lungs of frogs and dogs under a microscope, discovered in them small air saccules that were attached to the small diverticula of the lungs' windpipes. Much to his surprise, he discovered that air in these saccules did not come into contact with the blood. The blood was trapped in minute blood vessels that kept it separate from the air. He named these blood vessels capillaries, since they were as fine as hairs. Malpighi's discovery of these tiny vessels proved the existence of a physical connection between the arterioles and the veins, substantiating Harvey's reasoning and completing his system for the circulation of blood. It was later discovered that the thin walls of the capillaries enable the flow of oxygen and carbon dioxide between the blood and the tissues of the body.
Although Harvey demonstrated that the flow of blood washed the lungs from the heart's right side and returned to its left, thus being transformed from venous to arterial blood, the nature of the blood's transformation and how it occurred were not at all clear to him. Like others of his time, he could only speculate regarding the nature of this transformation. Some believed that the blood fermented in the lungs, consequently becoming lighter and paler, which would account for the change in its color from dark venous to red arterial blood. Others thought that air finds its way into the blood through small perforations in the lungs, subsequently mixing with it and making it lighter. No one, however, succeeded in actually seeing these air openings in the lungs.
The Italian physician Alfonso Giovanni Borelli eloquently expressed the confusion regarding the function of breathing when he wrote, "It is clear from what has been said that the use of breathing is not the cooling of the excessive heat of the heart, nor the ventilation of the vital flame, nor the mixture of the heterogeneous part of the blood ... but so great a machinery of vessels and organs of the lungs must have been instituted for some grand purpose."
Many more years of original thought and experiments were required before the process of breathing was understood in detail. An important contribution came from four young scientists at Oxford University in England during the course of the seventeenth century. Robert Boyle, the seventh son and fourteenth child of the Earl of Cork, was born in 1627. As a scion of a family rich in property, Boyle never had to concern himself with his livelihood, and he dedicated his wealth and talents to science. Although he is better known for Boyle's law, which maintains that the pressure of a given quantity of gas varies inversely with its volume, his work on the significance of breathing was a precursor for all who came after him. Boyle was the first to prove by means of a scientific experiment, in which he used an air pump that had just been invented, that air is vital to the existence of life. In his journal he wrote, "To satisfy ourselves in some measure about the account on which respiration is necessary to the animals that nature hath furnished with lungs, we took ... a lark ... which being put in a receiver ... [and] the vessel being hastily, but carefully closed, the vacuum pump was diligently plied, and the bird for a while appeared lively enough; but upon greater exsuction of the air, and very soon after was taken with as violent and irregular convulsions, as are wont to be observed in poultry, when their heads are wrung off ... and died."
In a series of experiments using a vacuum pump, Boyle proved that air, and not the actual motion of the thorax when breathing, is the vital element in the process called breathing. Extracting the air from a receptacle containing a scurrying mouse and a burning candle caused the mouse to die and the candle to be extinguished, which demonstrated that both depended on air for their existence.
Robert Hooke, Boyle's assistant and the second member of the Oxonian quartet, was blessed with remarkable technical talent. At the age of twenty-five, he completed his studies at Oxford, where he was renowned for his technical inventions, which included improved air pumps, gauges, microscopes, and even meteorological measuring instruments. Some claim that through his instruments Hooke was the first to hear the sounds of the heart and lungs, preceding the invention of the stethoscope by about 150 years. His technical ingenuity was rewarded when he was appointed curator of the Royal Society of London at twenty-seven. He was charged with conducting scientific experiments before members of the Society, to demonstrate physical, chemical, or physiological principles. The Society, which started in 1645 as a circle of fellows of a "particularly inquisitive and investigative character" who gathered informally to discuss philosophical and scientific matters, was recognized by King Charles II in 1660 and incorporated as the Royal Society of London for the Advancement of Science. The Society provided a valuable forum where persons interested in knowledge of the natural world could present original and innovative ideas, refute existing theories, and conduct scientific experiments in public. Membership fees were one shilling a week, which went toward defraying the cost of the experiments.
On October 24, 1667, Hooke impressed members of the Royal Society with a demonstration of artificial respiration. The experiment, which was reported in the Society's official publication in just 710 words, complemented Boyle's ideas and expanded on them. Hooke surgically opened a dog's chest and, using two interlinked bellows, succeeded in continuously filling its lungs with air, so that there was no movement of the thorax or lungs. Small punctures he had made in the pleura allowed the air to escape, and he succeeded in keeping the dog alive for a prolonged period. The results of this experiment led Hooke to the positive deduction that "the bare Motion of the Lungs without fresh air contributes nothing to the life of the Animal, he being found to survive as when they were not mov'd as when they were; so it was not the subsiding or movelessness of the Lungs, that was the immediate cause of Death, or the stopping of the Circulation of the Blood through the Lungs, but the want of a sufficient supply of fresh air." Hooke's experiments, however, proved only that the supply of air is vital to life; they did not solve the mystery surrounding the question of why it was so vital. What actually takes place in the lungs? How does air flowing to the lungs support the existence of life?
The third of the Oxford researchers, Richard Lower, completed his medical studies at the university in 1665, the year of the Great Plague in London, and a year before the Great Fire of London, which almost destroyed the city. Like all his contemporaries, Lower committed to memory the Galenic doctrine holding that the function of the heart was to create heat, which is carried to all parts of the body through the blood, whereas the function of the lungs was to cool the heart. But Lower did not believe his teachers. In those days it was already known that the color of arterial blood is bright red, whereas venous blood is much darker. The difference in color was ascribed, as mentioned earlier, to a process resembling fermentation or combustion occurring in the heart. Lower regarded the change in the color of blood as essential to understanding the correlation between the heart and the lungs. He observed that the color of a blood clot's exterior pales when exposed to air, and he asked whether this was possibly similar to what happens to blood when it passes through the lungs. Hooke's experiment in artificial respiration provided him with an idea for how to test his hypothesis.
Lower examined the color of blood as it flowed from the lungs to the heart in animals that were kept alive by artificial respiration.
Excerpted from Restless Nights by PERETZ LAVIE Copyright © 2003 by Yale University. Excerpted by permission.
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