Insomnia; and Other Disorders of Sleep

by Henry M. Lyman

It is not often that the sense of smell becomes the avenue of impressions that interfere with sleep. So different are the capacities of individuals in this particular that an odor which might severely annoy one person, would pass almost unnoticed by another. Large cities are sometimes invaded by overwhelming stenches from the various factories which spring up in their neighborhood. While it is seldom true that the vapors discharged by such establishments are directly deleterious to health, they may become indirectly a cause of ill-health through the wakefulness occasioned by them among weakly invalids. The smell of smoke in a bed-chamber sometimes serves to awaken a sleeper, giving warning of the outbreak of a fire in the building. Less energetic odors may disturb the depth of sleep without actually waking the patient. Thus Maury records[31] that when he was made to inhale the vapor of cologne water while asleep, he dreamed of being in the shop of a perfumer.

Excitement of the sense of taste would, doubtless, operate in a similar manner; but it is so difficult to arouse this sense without at the same time irritating the nerves of common sensation about the mouth, that very little can be said regarding the matter. Dreams of gustatory sensations are usually of subjective origin, dependent upon some reflex movement, or upon some agitation of the organ of memory, within the brain.

If, with Sir William Thompson,[32] we recognize a sixth sense—the sense of temperature—it must be admitted that through the varying sensations of heat and cold, sleep can be greatly disturbed. Every one will recall to mind the story told by Dugald Stewart, of a gentleman who dreamed of walking over heated lava on Mt. Ætna when a bottle of hot water was placed against his feet, in bed, on account of some slight indisposition. The temperature of the air is one of the most important factors in the determination of sleep. A high temperature keeps every one awake—a fact well known among the unfortunate denizens of the garrets in our great cities. Not only is wakefulness the direct result of heat, but it is aggravated and embittered by the accompaniments of a torrid climate—insects, foul air, and cutaneous disorders. In the East Indies, so difficult is sleep under such conditions that the wealthy inhabitants compel their servants to cool them all night with the punkah, a large, swinging fan, suspended above the bed, and kept in motion by means of a cord leading outside of the bed-room to the verandah, where the punkah-wallah sits and pulls the string while his master sleeps. So powerful is the force of habit in the organization of the automatic apparatus of the body that, though these punkah-pullers often fall asleep, they still continue, without interruption, the successive movements by which the fan is kept in operation.

The evil effects of a high temperature are greatly aggravated by the presence of humidity in the atmosphere. Dampness interferes with the process of exhalation from the surface of the body, which, consequently, tends to become overheated. The tissues, under such circumstances, are imperfectly defecated, and rapidly pass into a condition of imperfect nutrition. This depresses all the functions of the body, and renders the nervous system inordinately irritable. Sleep cannot be profound and refreshing, because of the over-excitable state of the brain. During the long, hot season in tropical countries, it often becomes necessary to seek a temporary retreat among the highlands and mountains, in order to find a climate sufficiently dry and cool to furnish the condition for refreshing sleep. For the same reason many of the inhabitants of the Southern United States are forced to spend the summer months in the invigorating atmosphere of Minnesota and Northern Michigan. One of the most delightful of experiences may be procured on any warm day in summer by embarking, at Chicago, upon one of the steamboats bound to Mackinac. At the wharf, in the hottest and dirtiest part of the city, all is dust, perspiration, and discomfort. The wide cabins are filled with people who are tired, thirsty, and discouraged. Sickly, squalling babies swarm in numbers sufficient to drive one mad. As the sun goes down, the signal-whistle sounds, head-lines and stern-lines are quickly cast off, the propeller churns the mire behind the boat. Slowly swings the huge fabric away from the shore, gliding between the walls of sun-scorched brick that line the stream on either side. At last the light-house at the mouth of the river is passed, and we are out upon the blue waves of Lake Michigan, with a heavenly breeze searching every crack and cranny of the hull. New life animates every form, and presently a great silence pervades the brilliant cabins. The children have left their woes behind, and, for the first time, in many weeks, perhaps, they and their weary mothers sleep the sleep of innocence and peace.

The dependence of a high atmospheric temperature upon the direction of the wind renders the course of the aerial currents a matter of great importance in relation to sleep. The southerly winds which, in the northern hemisphere, are hot and enervating, always produce an increase of wakefulness. The winds that blow from the heated deserts of Africa, Arabia, and Australia, are greatly dreaded upon this account, as well as for the other numerous discomforts which fly in their train. Their cessation, and their replacement by a cool, polar current brings relief at once. The changes thus produced in the electrical condition of the atmosphere doubtless contribute more than is usually known to these results. A cloudless sky gives evidence of positive electricity, which is much stronger in winter than in summer.[33] Clouds are sometimes positive and sometimes negative. According to Fonssagrives[34] the atmospheric electricity is positive during northerly winds, and negative during the prevalence of winds from the southerly quarters of the horizon. Great disturbances of the electrical condition of bodies is often observed during the occurrence of the sirocco in North Africa. Arago has related the case of an officer in the French army[35] who saw sparks of electricity leaping from his epaulettes at every blast of the sirocco encountered on a march in the neighborhood of Algiers. Such atmospheric disturbances often produce very disagreeable effects upon persons of a nervous temperament. According to Fonssagrives (loc. cit.) such patients frequently experience, during the prevalence of storms which traverse great distances, a high degree of insomnia, together with headache, pains in the limbs, joints, and old injuries, and a general indefinable sensation of discomfort. S. Weir Mitchell has carefully traced the connection between these phenomena and the variations of barometric pressure which accompany the revolving storms that cross the continent in a northeasterly direction.[36]

Though the effect of a high atmospheric temperature is unfavorable to sleep, an excessive temperature produces the opposite condition. Stupor rather than sleep is the consequence of insolation and of exposure to great heat from artificial sources. This is a pathological process, and, therefore, must not be mistaken for natural sleep. It may result either from cerebral congestion, or from cardiac exhaustion, and is characterized by an extraordinary bodily temperature and a high rate of mortality.[37] So elaborate are the arrangements for the preservation of a uniform temperature throughout the body that it is practically impossible for a sunstroke to occur unless the regulative apparatus has been previously deranged by ill-health.

Excessive cold operates in like manner to produce a condition of stupor that tends to a fatal termination. But moderate degrees of cold act as excitants of wakefulness. By effecting a contraction of the vessels of the skin cutaneous circulation is impeded. The venous side of the circulatory apparatus becomes overloaded with blood; the exhalation of carbonic acid and the production of heat are reduced. The discomfort that results from this disturbance of the natural functions of the tissues is sufficient to arouse the brain to wakefulness, just as an imperfect oxidation of the blood serves to excite the respiratory centre in the medulla oblongata. It is hardly necessary to allude in this connection to the increased flow of blood through the brain occasioned by this as by every other excitement of the sensorium. Local refrigeration of any portion of the body thus acts as a painful excitant of the cerebrum, and produces wakefulness, very much as distention of the intestines with gas will keep one awake. It is for this reason almost impossible to sleep with cold feet. Conditions of this sort are pathological, and are far in excess of the agreeable coolness which favors sleep. The effects of progressive diminution of the temperature of the air are well illustrated by the hibernation of animals.[38] As the temperature of the air diminishes, in winter, animals like the marmot fall into a species of sleep. Their movements of respiration and circulation are greatly reduced, and their bodily temperature falls, though it always remains several degrees above the temperature of the surrounding air. So long as the average degree of cold is maintained, the little creature sleeps naturally; but, if the air becomes extraordinarily cold, the physiological repose of the animal is disturbed. It becomes uneasy, wakes up, and seeks a warmer retreat. Too great a degree of cold thus becomes a cause of wakefulness. If the animal under these circumstances fails to secure protection against a falling temperature, it passes into a state of lethargy that is often fatal—a pathological condition being substituted for the physiological sleep of ordinary hibernation. In like manner the human animal may experience the threefold effects of refrigeration: first a pleasing coolness that favors sleep; then an uneasy sensation of cold which causes wakefulness; and, finally, a lethargy that paralyzes all the functions of the body and terminates in death.

2. Affections of the nerves of common sensation.—Chief among the causes of sleeplessness thus produced is pain. This is a modification of feeling, caused by excessive or extraordinary excitement of the peripheral nerves of sensation. The seat of the excitement may be in the skin or in the deeper tissues of the body. Cutaneous pain may be caused by the activity of various insects, like flies, mosquitos, fleas and bedbugs, or by the presence of certain parasites, such as the itch-mite, or by ordinary diseases of the skin, of which notable examples are found in erysipelas, erythema, urticaria, lichen, prurigo, certain varieties of eczema and psoriasis. The troublesome forms of pruritus which accompany icterus, or which may occur without any clearly defined cause, are frequent causes of wakefulness. The last mentioned disorder must, however, be sometimes recognized as a consequence of central nervous disorder, rather than a result of peripheral disease. Witness the frightful itching sometimes experienced during the progress of chronic myelitis. All kinds of injuries, wounds, ulcers, and other local inflammations are common causes of insomnia by reason of the painful impressions transmitted from them to the brain. Hence the great importance of anodynes and hypnotic remedies in the course of surgical practice. Diseases or injuries of the various peripheral nerves are notable causes of sleeplessness. Witness the horrible wakefulness caused by neuritis and by neuralgia. The development of neuromata in the stumps of amputated limbs may thus become a most painful cause of insomnia. Inflammations which encroach upon sensitive nerves produce intense pain with consequent loss of sleep. Of this very conspicuous examples are furnished by spinal meningitis, and by the effects of local periostitis causing compression of the branches of the fifth pair of nerves.

3. Affections of the sympathetic nerves.—So much still remains to be learned concerning the pathological functions of the sympathetic nerves that it is impossible to assign with any great degree of precision the exact amount of interference with sleep that may depend upon disordered conditions of this portion of the nervous system. Since their principal functions consist in the regulation of the flow of blood and lymph throughout the body, and in the control of the processes of nutrition, calorification, secretion and excretion, it follows that any considerable derangement of their healthy action must be represented by a corresponding disturbance of the brain. This may reach the field of consciousness in the form of pain, and thus may become a cause of sleeplessness. In all the phenomena of inflammation sympathetic nerves play an active part. In certain portions of the body, as in the principal viscera, and in the periosteal covering of the bones, they are the interstitial nerves of the structures. When the body is in a healthy condition these nerves convey impulses of a sensory character which do not reach the cerebral organ of conscious sensation. But in certain morbid states they become inordinately sensitive, and they then serve to convey and probably also to magnify sensations to an extent that may cause exquisite pain with all its consequences. Witness the pain experienced during the various forms of colic. Rheumatic inflammations, pleurisy, pericarditis, peritonitis, cystitis, metritis, ovaritis, gastro-enteritis, and other similar diseases owe their principal suffering to the affection of the sympathetic nerves connected with the respective organs which become the seat of pain. Including with the sympathetic nerve the pneumogastric nerve, which occupies a functional position between the strictly peripheral and the ganglionic nerves, all the various forms of pain and uneasiness experienced in the region of the heart and of the lungs may be assigned to this system of nerves. Thus the various species of respiratory disturbance, such as asthma and dyspnœa from any cause, and the forms of palpitation and other cardiac disorder may become causes of wakefulness. In like manner the vague and uneasy sensations associated with certain varieties of dyspepsia are frequent sources of sleeplessness, not merely by reason of the pain which they occasion, but also because of the general disorders of nutrition with which they are associated.

II. Insomnia caused by morbid states of the central nervous organs.