17.
Obstructive sleep apnoea and snoring
The phenomenon of snoring although considered humorous is far from trivial for those who suffer from it. As we have seen in this section, inspiration is brought about by expansion of the lungs producing a negative pressure within the airways, which draws air into the lungs. This negative pressure tends to cause the airways to collapse, particularly the extrathoracic airways which are not surrounded by negative intrapleural pressure. Of the extrathoracic airways, the nose is surrounded by bone and the trachea supported by cartilaginous rings. The pharynx, however, is bounded anteriorly by the genioglossus muscle of the tongue and the soft palate and laterally by muscular walls.During REM (rapid eye movement) sleep there is a general relaxation of muscle tone which may be sufficient to allow the negative intraluminal pressure to collapse the pharynx. The characteristic rattling sound of snoring is the subject dragging air through this collapsed section of airway.It is thus an encouraging sound, signalling success in ventilation. The snorer falling silent, far from being a cause for joy, can have sinister implications. He, and it is most frequently he, may have been momentarily awakened by the obstruction, and this cycle of falling into REM sleep, airways collapse and awakening may occur literally hundreds of times each night. These awakenings are too brief for the patient to be aware of them but they deprive him of essential REM sleep. He suffers personality changes due to this deprivation and may take \'micro-sleeps\' during the day, with possible fatal consequences if he is driving or operating machinery.Alternatively, the snorer\'s silence may signal a total cessation of breathing. Under these circumstances desaturation of the blood can embarrass the myocardium to a degree that is eventually fatal. The problem of obstructive sleep apnoea can be so serious that patients have resorted to surgery to tighten up the muscles of the pharynx or even to a tracheostomy to bypass the pharynx altogether. A modern, less traumatic, equally effective form of treatment consists of pressurizing the air in the pharynx with air from a blower administered via tubes in the nostrils or by a face-mask. A pressure of 1 kPa is all that is required and it is not yet known whether the therapeutic effect is a simple inflation of the pharynx or whether there is a reflex stimulation of pharyngeal muscle tone.
18.
Osteoporosis
This term literally means \'porous bones\'. Compared with normal sturdy bones, the bones are sponge-like, insubstantial and brittle. This condition is usually diagnosed from the X-ray appearance when the bones appear less substantial and, particularly, less dense than normal. As with a number of medical terms, the same word is used for a clinical state, a pathophysiological concept and a radiological appearance.The clinical state consists of features such as pain, deformities and fractures caused by relatively slight force on a bone weakened by disease (pathological fractures). Normally, a young person\'s femur will only fracture when subjected to severe force as in a road traffic accident. However, the osteoporotic femur of an elderly person may fracture spontaneously because of the normal stresses of weight bearing. The pathophysiological concept is of a bone that has gradually wasted, particularly through the loss of its collagen fibres, so that the calcium salts are not adequately reinforced. The radiological appearance is of bones that cast relatively thin pale shadows. How do we put these concepts together?A good place to start is with the dictionary definition of osteoporosis (Dorland\'s): \'abnormal rarefaction of bone, seen most commonly in the elderly\'. This draws attention to the effect of age. In fact, the bones of normal people grow and become denser and stronger during childhood and into early adulthood. Genetic, hormonal, nutritional and activity factors play a part in the ultimate strength in early adulthood, and thereafter bone strength gradually declines. Male bones in general are much stronger than female bones - so much so that one of the ways the sex of skeletal remains found by archeologists is determined is by the size and ruggedness of the long bones, with generally a clear gap between the male and female femur in terms of bulk. This is likely to be related to the increased strength of male muscles, because the pull of muscles and the stresses of gravity combine to develop strength in such bones. Having started smaller, female bones tend to decline in strength more rapidly than male bones, particularly after the menopause. Thus, in octagenarians and nonagenarians the problems of osteoporosis are largely, though not entirely, confined to females. Collapse of vertebrae with curvature of the spine (kyphosis) and loss of height are one manifestation. A more drastic effect is fracture of the femur, referred to above. This may lead to serious illness and death in some cases, but modern techniques of repair with a metal plate or other prosthesis can often avoid this and lead to quite rapid recovery.The above description refers to the common form of osteoporosis, related to age. The condition can also occur in younger people when the fibrous collagen matrix (which acts like the steel reinforcing in reinforced concrete) is attacked by certain hormonal disturbances. One of these is excessive glucocorticoid activity, which can be due to adrenal tumours, but is more often due to therapeutic administration of the glucocorticoids (e.g. prednisone) for conditions such as rheumatoid arthritis, asthma and polymyalgia, and to patients with organ transplants to prevent rejection. Excessive thyroid activity can also lead to a catabolic state in which the protein collagen fibres of bone are broken down.To prevent osteoporosis as far as possible, children, particularly females, are encouraged to ensure an adequate calcium intake mainly in the form of milk and to exercise adequately to build up strong bones. Adequate calcium and exercise should be continued throughout life - not to prevent loss of bone mass (which seems at present inevitable), but to minimize the rate of loss. Postmenopausal hormone replacement can help to reduce the rate of bone loss, and calcium supplements may help in situations where the condition is marked (assessed by bone scanning) or where glucocorticoid therapy increases the risk of osteoporosis.Finally, osteomalacia can be mentioned. It literally means softening of the bones and it can produce similar effects to osteoporosis. Strictly speaking it is a pathophysiological condition due to inadequate calcium salts in bone (compare inadequate collagen in osteoporosis). This may be due to lack of calcium in the diet or to lack of activated vitamin D (dihydroxycholecalciferol), which is needed for adequate absorption of calcium. In children, because the bones are indeed particularly soft, deformities may be marked (rickets) with severe curvature of spine and leg bones. In adults, the effects are more like those of osteoporosis.
19.
Parkinson\'s disease
Parkinson\'s disease (paralysis agitans) is one of the best known of the diseases affecting motor function. It is a neurodegenerative disorder with highly characteristic symptoms which were first documented by James Parkinson in 1817 as \'involuntary tremulous motion, with lessened muscular power in parts not in action and even when supported with a propensity to bend the trunk forwards, and to pass from a walking to a running pace: the sense and intellects being uninjured\'. With the exception of the last phrase, this description remains largely accurate.The most common form of Parkinson\'s disease, which affects about 1 in 1000 of the population, is idiopathic (that is, it arises spontaneously and without apparent cause) and usually appears after the age of 50. Parkinson\'s disease is characterized by pronounced tremor at rest and rigidity of the muscles, both of which are positive signs, and by bradykinesia (slowness of movement, particularly in its initiation), which is a negative sign.In the 1950s it was found that dopamine constitutes almost 50% of the catecholamine in the brain and that 80% of it is located within the basal ganglia. Post-mortem studies of the brains of people who had suffered parkinsonism revealed that there was a substantial reduction in the levels of dopamine. Subsequent studies revealed the characteristic loss of the dopaminergic neurones from the substantia nigra (other regions are also affected, including the nucleus coeruleus) which project onto the striatum of the basal ganglia (the nigrostriatal pathway). It is proposed that the loss of this inhibitory input to the striatum results in excessive inhibitory output from the basal ganglia to the thalamus, affecting the motor functions.Current treatment centres around the administration of l-dopa (3,4-dihydroxyphenylalanine, or its analogues) which is an amino acid precursor of dopamine and which can cross the blood-brain barrier. This treatment serves to reduce the symptoms of Parkinson\'s disease but does not affect its progression. Recently, studies have been carried out into the effect of implanting fetal cells into the basal ganglia. These fetal cells appear, in some cases, to be maintained and to be capable of synthesizing dopamine, though the initial promise of such studies remains unfulfilled. Another approach to the investigation of the disease has come to light as a result of the discovery of the action of the substance MPTP, which can be a contaminant of heroin. This has enabled the development of models of parkinsonism and thereby greatly enhanced our ability to investigate the disease.Disorders of the motor system, due to experimental or accidental lesion or due to disease, have played and continue to play a key role in our understanding of the functions and integration of the different structures and pathways within the nervous system.
20.
\'Pink puffers\' and \'blue bloaters\'
These picturesque piscine terms are used to differentiate between two major types of respiratory patient with chronic obstructive pulmonary disease (COPD) and represent the two extremes of a spectrum between pure bronchitis and pure emphysema, two conditions which very rarely exist in their pure state.Pink pufferThis patient (sometimes referred to as Type A COPD) appears to be \'fighting his disease\'. He is tachypnoeic, dyspnoeic and frequently breathes with pursed lips. Blood analysis reveals a mild hypoxaemia, if any, and a normal haematocrit. This patient is predominantly suffering from emphysema.Blue bloaterOn the other hand, this patient (Type B COPD) appears to be \'not fighting his disease\'. He provides a history of cough producing sputum on most days for at least 3 months of the year for more than 1 year. He is cyanotic secondary to hypoxaemia. Blood analysis also reveals hypercapnia and increased haematocrit. His legs are swollen, and distended neck veins point to right-sided heart failure. This patient is primarily suffering from chronic bronchitis.In the vast majority of patients, chronic bronchitis and emphysema coexist and the clinical presentation is mixed. Lung function tests, of course, reveal airway obstruction and there will be an increase in lung volumes where emphysema predominates. In this case, transfer factor will be markedly decreased. The chest X-ray of the predominantly emphysematous patient shows overexpanded lungs pushing down and flattening the diaphragm, with lung fields lacking the usual markings and vessels because of tissue destruction.It is fortunate that an exact quantification of the proportions of chronic bronchitis and emphysema is not important in practical terms for treatment and management of these patients, for whom the most important aspect of management is stopping smoking, the most important factor in the aetiology of the disease. |
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