The Respiratory System
3.3a The physiology of the respiratory system
This section concentrates on the physiology and pathology of the respiratory system, looking at the structure and function of the respiratory system in health.
The role of the respiratory system51
As described earlier in Section 1.1b, oxygen is one of the essential ingredients for the process of cellular respiration. The respiratory system is specialized to enable an adequate supply of oxygen to the tissues. It is also the role of the respiratory system to allow carbon dioxide, a waste product of respiration, to be removed from the body.
In common usage, the term respiration refers simply to the act of breathing. However, in physiology there are three aspects to respiration that can be clearly defined. These are external, internal and cellular respiration.
The respiratory system is primarily concerned with external respiration, which is indeed the process of breathing. This leads to the exchange of gases between the blood and the lungs.
Internal respiration is the exchange of gases between the blood and the cells of all the body tissues, and is one of the functions performed by the circulatory system.
Cellular respiration is the process (described in Section 1.1b) by which oxygen and nutrients are converted to cellular energy (adenosine triphosphate (ATP)) and carbon dioxide within the cell itself. It is important to be clear about the distinction between these three processes, as these terms help define the precise roles of the respiratory system.
The respiratory system is conventionally divided into two sections, the upper and lower respiratory tract. A simple representation of the organs of the respiratory tract is given in Figure 3.3a-I. The division between the upper and lower parts occurs at the point at which the trachea splits into the two tubes called bronchi.
The diagram illustrates that this division occurs at a deep level in the chest, just above the position of the heart. It also illustrates the close physical relationship between the heart and the lungs. In fact, if the heart is removed through dissection, an imprint of its shape is seen in the tissue of the lungs.
Figure 3.3a-I The organs of respiration
The upper respiratory tract
The upper respiratory tract leads from the entrance of the respiratory system at the nose to the end of the trachea, the tube that directs the inhaled air into the chest cavity (thorax) towards the lungs.
The function of the upper respiratory tract is to provide a plentiful supply of warm, clean and moist air to the lungs. To help it perform this function it consists of wide air spaces and is lined by a specialized form of epithelium. The respiratory epithelium consists largely of ciliated columnar cells, but it also has many mucus-secreting (goblet) cells.
The water-containing mucus moistens the air that rushes through the respiratory tract, and picks up dirt particles and other foreign bodies present in the air. Cilia are structures akin to microscopic hairs on the surface of cells. They are powered by the energetically charged molecule ATP to move in coordinated waves. In the respiratory tract the cilia beat in an upward direction. Their function is to cause an upward movement of the mucus, allowing the foreign material to be moved away from the delicate lung tissue and up to the back of the throat, from where it can be swallowed or expectorated.
The connective tissue layer below the respiratory epithelium has a number of lymphocytes scattered throughout its length. These respond to foreign antigens by producing antibodies and attracting other immune cells. This is an important aspect of the protection of the respiratory tract from infection.
The important parts of the upper respiratory tract are the nose, pharynx, larynx and trachea.
In the breathing of a healthy person at rest, all air is drawn in through the nostrils into the nasal cavity. This space has a deeply ridged surface that has a rich blood supply. This means that the current of air comes into contact with a large area of warm epithelium before its descent towards the lungs. In addition to the cilia on the epithelial cells, body hairs are present in the opening of the nose to filter out any large foreign particles.
Opening out into the nasal cavity are the sinuses. These are cavities deep within the facial bones that have narrow passageways leading into the nasal cavity. Their function is to give the voice a resonant quality, the loss of which is apparent in anyone who has suffered from a head cold, when the sinuses become filled with thick secretions. A tiny duct leading from each eye also opens into this space. This continually drains away tears from the eyes. The runny nose that accompanies a bout of crying is a result of the excess tears flooding into the nose through this duct.
The nose is the specialized sense organ for smell. To perform this function, delicate nerves originating from the base of the brain penetrate the bone above the nasal cavity to supply the nasal lining. These are sensitive to the chemicals in the incoming air, which become dissolved in the mucus. The sense of smell is also important to enrich the experience of taste. Occasionally, in a head injury, these nerves become permanently severed, even though there may be no other major brain damage. The person may recover fully but be left without a sense of smell and with a highly impaired sense of taste.
Other nerves in the nose are very sensitive to the irritation that can result from foreign particles and from inflammation of the lining of the nose. These nerves can trigger the protective reflex of the sneeze, which is a very effective mechanism for expelling unwanted material from the nasal cavity.
The pharynx is the space at the back of the nose that connects with the throat. The adenoids (nasal tonsils) are two collections of lymph node tissue situated at the back of this space. The tonsils (palatine tonsils), which are similar collections of lymphoid tissue, are situated a little lower down. The palatine tonsils can be seen in most people on either side of the space behind the arch of the palate, as illustrated in Figure 3.3a-II, whereas the adenoids are hidden up behind the palatoglossal arch.
Figure 3.3a-II The location of the palatine tonsils
The function of the tonsils is to complement the protective function of the lymphocytes in the respiratory epithelium. Their presence is an indication of the need for the lungs to be protected from foreign material. The adenoids are most active in early childhood, because this is the time when immunity to a wide range of infections has to be rapidly developed. After reaching five years of age, the adenoids usually shrink to a negligible size, although the palatine tonsils persist into adulthood.
The Eustachian tube opens from the middle ear into the pharynx close to the location of the adenoids. The middle ear is also lined with respiratory epithelium, and the Eustachian tube allows the drainage of mucus from this enclosed space.
The larynx, popularly known as the voice box, is the structure that separates the pharynx from the trachea. Although it is primarily associated with voice production, it also plays a very important protective role. Figure 3.3a-III is a diagrammatic representation of the nasal cavity, pharynx and larynx, which illustrates how these structures relate to each other.
Figure 3.3a-III The pathway of the air from the nose to the larynx
The tube-like larynx has stiff cartilage in its walls that enables it to maintain its shape. The cartilage at the front of the larynx is what can be seen and felt as the “Adam’s apple.” Because the thyroid gland sits close to this structure, the medical term for this is the thyroid cartilage.
The vocal cords are two fine flaps of tissue that are suspended from the surrounding cartilage tube. Figure 3.3a-IV shows a view of the aperture of the larynx. The vocal cords are depicted on either side of the aperture, leaving a triangular space through which the air can pass. Tiny muscles in the larynx contract to change the shape of this triangle between the vocal cords so that the space can vary from being a wide gap to a tiny chink. The tone of the muscles also affects the tightness of the vocal cords. During quiet breathing the gap is wide to allow a free passage of air in and out of the lungs. During speech, the gap narrows and the cords tighten. The expired air causes vibration of the tightened cords, which produces the sound of the voice. The tighter the cords are the higher the pitch of the voice.
Figure 3.3a-IV The interior of the larynx, viewed from above
The protective reflex of the cough involves a temporary tightening of the vocal cords so that the gap closes altogether. This occurs during a forced expiration of air. The closed gap means that the pressure of air below the vocal cords is suddenly increased. At this point the muscles relax and the gap widens. This results in a sudden forceful rush of air accompanied by the familiar sound of the cough. Like the sneeze, the cough is stimulated by the irritation of nerves in the larynx and the tubes that branch from the trachea into the lungs. The cough also has the effect of expelling unwanted material from the trachea, larynx and pharynx out through the open mouth.
The other important protective structure in the larynx is a stiff flap of cartilage-containing tissue called the epiglottis, which sits above the larynx. During swallowing this flap descends to completely cover the gap between the vocal cords. This protects against the inhalation of food during swallowing.
The trachea is the wide tube that descends from the larynx to the division of the bronchi deep within the thorax. It is held open by rings of cartilage within its walls and is also lined by respiratory epithelium.
The lower respiratory tract
The lower respiratory tract begins where the trachea divides into the two narrower tubes called the bronchi. The bronchi further subdivide, like the branches of a tree, to penetrate the tissue of the two lungs.
The bronchi and bronchioles
The bronchi and the smaller tubes into which they divide (the bronchioles) are structurally similar to the trachea, and are also lined with respiratory epithelium. Therefore, they, too, are concerned with ensuring the air that reaches the depths of the lungs is as warm, moist and as clean as possible.
The width of these air passages varies according to need. During exercise the bronchi and bronchioles widen, so that a large amount of air can enter the lungs in each breath. At rest, they narrow again because the need for a large volume of air is not so necessary, and because the protective mechanism of these tubes is more efficient when they are narrower.
At the end of each of the tiniest branches of the tree-like air passages that penetrate the lung are masses of tiny air sacs only a few cells in diameter. These are known as alveoli (singular alveolus). The lungs are composed of millions of these tiny air spaces packed together, and all connecting with the outside world through the bronchioles and bronchi. The alveoli are lined with only a single layer of flat squamous epithelium, and are supplied by a dense network of fine blood capillaries.
Figure 3.3a-V illustrates how the alveoli branch from the bronchioles, and how a network of capillaries supplies each one.
Figure 3.3a-V An alveolus and its capillary network
EXCHANGE OF GASES IN THE ALVEOLI
The blood that enters the capillaries surrounding the alveoli has originated from the pulmonary arteries. These large vessels originate from the right ventricle of the heart and carry deoxygenated blood pumped by the right side of the heart. The blood is deoxygenated because the cells of the body tissues have used up all the oxygen in the process of cellular respiration. As well as being deoxygenated, this blood is also carrying a high concentration of carbon dioxide, the by-product of cellular respiration. In contrast, the air inspired into the alveoli is rich in oxygen from the outside air, and carries very little carbon dioxide. Therefore, there is a tendency for the oxygen in the alveoli to move into the deoxygenated blood in the capillaries. This movement occurs readily, as oxygen can diffuse with no restriction through the cell membranes of the alveolar and capillary walls. At the same time, there is a movement of carbon dioxide out of the capillary blood and into the alveolar air. This exchange of the two gases of respiration occurs very rapidly.
The capillaries that leave the alveoli converge to form the pulmonary veins, which return all this blood to the left side of the heart. This blood is now rich in oxygen, and has been cleared of carbon dioxide. The pulmonary veins are the only veins in the body that carry oxygenated blood. All the other veins carry blood away from the body tissues, and this blood is, of course, deoxygenated.
The air left in the alveolus now contains more carbon dioxide than oxygen, and is expelled to the outside world by the process of expiration, so that the whole process can begin afresh with the next in-breath.
This process of exchange of gases is assisted by the fact that there are millions of alveoli, each with its own rich blood supply. In some conditions, such as emphysema, the delicate structure of the alveoli is damaged and their number is reduced (see Section 3.3e). This severely impairs the process of exchange of gases, so that the blood does not get replenished with an adequate amount of oxygen, and carbon dioxide fails to be fully cleared.
The lungs consist of the branching air passages of the bronchi and bronchioles, and the thousands of alveoli clustered around the ends of the bronchioles. The lungs are surrounded and supported by elastic connective tissue, which has the tendency to cause the fully expanded lung to contract. The lungs sit within the thorax, which is protected by the rib cage and its supportive muscles, and they rest on the sheet of muscle below known as the diaphragm.
The lungs are surrounded by a double layer of protective fluid-secreting serous membrane called the pleura. In the pleura the secreted fluid forms a thin lubricating layer between the two pleural membranes akin to the fluid that separates the pericardium from the heart. The outer pleural membrane is attached to the inner surface of the rib cage from above and at the sides, and to the diaphragm below. It is this attachment that prevents the elastic lungs from collapsing. Figure 3.3a-VI illustrates the relationship between the pleura and the lungs.
Figure 3.3a-VI The relationship of the pleura with the lungs
External respiration is the process whereby air is drawn into the lung tissue through inspiration and is then expelled through expiration. This process permits the exchange of gases to occur.
Inspiration involves the inflation of the lungs. Like an expanded bellows, the inflated lung naturally draws air into itself. The lungs are inflated by a lifting and expansion of the rib cage walls and a descent of the diaphragm. This action occurs as a result of contraction of the diaphragm and of the muscles that link the ribs together.
Expiration involves the deflation of the lungs. This naturally forces air back out of the lungs. In relaxed breathing, expiration requires no muscular effort. A simple relaxation of the rib cage and diaphragm has the effect of reducing the volume of the thorax and thus deflating the lungs.
In normal, quiet breathing the cycle of inspiration and expiration occurs at about 15 times per minute (4 seconds/cycle). There is an automatic reflex that originates from a control center in the base of the brain that sets this regular rhythm. Nerves travel down from this control center to stimulate the synchronized and rhythmic muscular contraction of the rib cage and diaphragm.
All variations in the resting respiratory rate are brought about by changes that take place in the breathing control center in the brain. The breathing control center is essential for maintaining homeostasis of the levels of oxygen and carbon dioxide in the arterial blood. The oxygen level must, of course, be maintained at a high concentration, whereas the level of carbon dioxide must not be allowed to rise too high. To perform this role, the breathing control center contains cells that are very sensitive to the level of carbon dioxide in the blood. A miniscule rise in the level of carbon dioxide leads to an increase in the breathing rate so that excess carbon dioxide can be breathed out of the body. If the level of carbon dioxide drops, so does the rate of breathing. The levels of carbon dioxide in the blood can then build up again.
The control center in the brain is also sensitive to drops in the concentration of oxygen in the blood. However, the responsiveness of the control center to carbon dioxide also indirectly controls the homeostasis of oxygen in the blood, as increased external respiration will increase oxygen levels, and reduced external respiration will reduce oxygen levels.
Any voluntary wish to modulate the breathing, such as for speech, singing or laughing, generates nerve impulses from other parts of the brain (the cerebral hemispheres) to the control center of breathing, which then alters the breathing rate accordingly. The sneeze and cough reflexes involve a direct link between the irritated nerve endings and the control center.
The way in which the brain is responsible for the voluntary and involuntary control of body functions is described in more detail in Chapter 4.1 on the nervous system.
Information box 3.3a-I
The lungs: comments from a Chinese medicine perspective
According to the Simple Questions (Suwen),52 the Lungs are “like a minister from whom policies are issued.” The functions of this Organ are to:
•govern Qi and respiration
•control channels and blood vessels
•control dispersing and descending
•regulate the Water passages
•control skin and body hair
•open into the nose
•house the Corporeal Soul (Po).
Government of Qi and respiration refers to two aspects, as described below.
Government of Qi
The Government of Qi refers to the conversion of Gu (food) Qi and Heavenly (Clear) Qi in the Lungs to produce Zong (Gathering) Qi. Zong Qi is important for supporting the Lungs, the Heart and the circulation. It also gives strength to the voice. The Lungs are therefore seen as the site of the combination of Gu Qi and Heavenly Qi into a readily available source of energy (Zong Qi) for the organs of the Upper Jiao, as well as for the circulation and the voice.
In conventional medicine no distinction is made between different sorts of energy as there is in Chinese medicine with the various types of Qi. There is also no idea that the Lungs play any role in the production of energy over and above their function in external respiration, which is to draw oxygen into the body.
However, conventional medicine recognizes that the lungs spring from the voice box region in embryology. A weak or hoarse voice can simply be a product of weak inspiration and expiration, as it is the force of the out-breath that controls the strength of the voice. The recurrent laryngeal nerve that controls the production of speech also runs deep into the thorax. The hoarseness that can characterize a case of lung cancer is a result of damage of this nerve by encroaching cancer.
Government of respiration
Government of respiration refers here to external respiration. This is a direct parallel with the understanding of conventional medicine. Strictly speaking, the role of the breathing control center in the brain would also be seen in Chinese medicine as part of the Lung functions, as it plays an important part of the control of external respiration.
Control of channels and blood vessels
There is no direct correspondence here with conventional medicine, as the channels are not conventional concepts, and the blood vessels are seen as part of the circulatory system. But actually, as Keown (2014)53 points out, the lungs are actually “more (blood vessel and) blood than lung” in that each tiny alveolus is cradled with a mesh of blood containing capillaries. In fact, the blood in our circulation is within the blood vessels of the lungs for exactly half of the time, and in this time is charged by life-giving oxygen and cleansed of acidic carbon dioxide.
Control of dispersing and descending
The dispersing function refers to the ability of the Lungs to spread Wei Qi and body fluids to all body parts. This protects the body from external pathogens and keeps the skin and muscles moist and warm. It is also important for the control of sweating. The lungs are not seen to have this sort of function in conventional medicine. Instead, the defensive and warming roles would be attributed to the immune system and circulatory system, respectively. Conventionally, the skin is seen as the organ that deals with sweating.
The descending function refers to the Descent of Qi, which is important to enable clearance of fluids via the Kidneys and Bladder, and also for defecation. If impaired, the loss of this function may give rise to edema, retention of urine and constipation.
However, in conventional terms there is no link between the lungs and the kidneys or the large intestine. Although the lungs can become waterlogged in a case of pulmonary edema, this is usually the result of a condition that primarily affects another part of the body, such as heart failure.
Regulation of the Water passages
This is part of the dispersing function of the lungs (see above).
Control of the skin and body hair
Again, there is little correspondence with conventional medicine, as the skin and body hair are not seen as linked to the function of the lungs. Although the common skin condition of eczema is commonly associated in conventional medicine with asthma, these are still seen as separate conditions. The reason they are understood to be linked lies in a deficiency of the immune system, not the lungs.
Opening into the nose
The nose is an organ of the respiratory system, so there is an obvious correspondence here with conventional medicine.
Housing the Corporeal Soul (Po)
The Po is the most physical aspect of the spiritual body and gives rise to clarity of thought and movement. Its health relies on a healthy rhythm of breathing.
In Chinese medicine it is believed that imbalanced emotions, in particular, grief and anxiety, will upset the pulsating rhythm of the Po by constraint of free movement of the chest.
Although conventional medicine makes no explicit link between the lungs and emotions or spirit, it is recognized that emotions have an effect, via the breathing control center in the brain, on the respiratory rate and rhythm, and also that mindful deep breathing can calm the emotions.
The Lungs in Chinese medicine have a much broader role than their purely physical counterpart in conventional medicine. It seems that the role of the Lungs in Chinese medicine also embraces aspects that would be attributed in conventional medicine to the cardiovascular, urinary, gastrointestinal and immune systems as well as the skin.
The functions of the Lung according to a conventional and Chinese perspective can be summarized in the form of a correspondence table. This illustrates the idea that the functions of what conventional medicine calls the lungs, including the air-filled sacs and the blood that circulates perpetually around them, may be the domain not only of the Lung Organ in Chinese medicine, but also of the Kidney and Liver Organs. It will follow from this that diseases of the lungs may manifest in Chinese medicine syndromes involving the Lung, Liver and Kidney Organs.
Correspondence table for the functions of the Lung, as described by conventional and Chinese medicine
Functions of the lung
Involved in the process of external respiration, which enables the exchange of oxygen and carbon dioxide between the circulation and the outside environment (Lung and Kidney Organs)
Helps to maintain a healthy balance of oxygen, carbon dioxide and acidity of the blood (Lung and Liver Organs)
Helps protect the body from noxious substances in the inhaled air (Lung and Kidney Organs)
Enables the production of a hormone (angiotensin) that is important in the maintenance of blood pressure (Kidney, Spleen and Heart Organs)
Very closely linked in structure and function to the heart on which they depend for an adequate supply of blood to oxygenate (Heart, Kidney and Liver Organs)
Provides a steady flow of air to power the production of speech from the larynx (Lung, Liver and Heart Organs)
Functions of the Lung Organ
“The Lungs are like a minister from whom policies are issued”
Governs Qi and respiration (respiratory system, process of cellular respiration that goes on in the mitochondria of all cells, circulatory system)
Controls the channels and the blood vessels (circulatory system)
Controls dispersing and descending (immune system, skin, large intestine, bladder)
Regulates the Water passages (circulatory system, kidneys, bladder)
Controls skin and (body) hair (skin, immune system)
Opens into the nose (nose, upper respiratory system)
Houses the corporeal soul (no correspondence to a physiological organ)
3.3b The investigation of the respiratory system
The bulk of minor respiratory disease, particularly infectious disease affecting the upper respiratory tract, is managed in the UK entirely by the doctor (general practitioner (GP)). More severe problems affecting the nose and throat may be referred for the opinion of a specialist in diseases of the ear, nose and throat (otorhinolaryngologist).
A patient with any other severe respiratory disease will be referred by their GP to a specialist in respiratory medicine. These doctors are commonly known as chest physicians.
If a surgical operation is necessary, the chest physician will refer the patient to a thoracic surgeon. Very often the thoracic surgeon is also skilled in heart surgery, in which case they are more accurately described as a cardiothoracic surgeon.
The most common investigations of the respiratory system include:
•a thorough physical examination
•laryngoscopy to examine the vocal cords
•microscopic examination of the sputum
•lung function tests to assess the mechanics of the breathing
•blood tests relevant to lung function
•chest X-ray imaging, computed tomography (CT) scans and bronchoscopy to visualize the lungs
•biopsy of the lung tissue
The physical examination of the respiratory system involves the stages listed in Table 3.3b-I.
Table 3.3b-IThe stages of physical examination of the lungs
General examination for signs of poor oxygenation of the blood (seen as the bluish discoloration of the lips and tongue known as cyanosis) and for the swelling of the base of the nails, known as clubbing (this is a sign of severe lung disease such as cancer and bronchiectasis)
Visual assessment of the rate and quality of the breathing
Physical examination of the chest for deformities, with the use of percussion to assess for any abnormal areas of dense tissue (indication of infection, fluid or tumor)
Auscultation of the breath sounds in all parts of the chest
This is an examination performed by an ear, nose and throat specialist to examine the vocal cords. It involves the skilled insertion of an instrument that carries a tiny mirror into the mouth and thence into the pharynx. It is usually painless.
Examination of the sputum
A patient with an infection or a possible tumor may be requested to produce a sample of phlegm. When examined by microscope, this can reveal the presence of infectious organisms, and occasionally, in cancer, will demonstrate cancerous cells. In the case of infection, the sample can be used to test for sensitivity to a range of antibiotics.
This simple non-invasive test involving a probe applied to the finger tips can give a rapid estimation of the blood oxygen levels, and is now an important aspect in the assessment of the severity of lower respiratory disease.
Lung function tests
Lung function tests are performed when disease of the lower respiratory tract is suspected. These tests require the patient to blow into a machine that measures the force and volume of the out-breath, and detects the changes that are characteristic of the diseases that lead to restricted breathing, such as asthma and emphysema. These tests are straightforward and painless for the patient to perform.
The most simple of these tests is the peak expiratory outflow assessment, which is done using a peak flow meter. This is a hand-held tool that the patient can be taught to use at home. Its main purpose is to assess the severity of asthma in a patient on ongoing treatment, although it does not provide as detailed or helpful information as the more complex tests available in a hospital outpatient department. A more complex examination of lung function includes assessment by means of a spirometer. This will provide a graphical computer printout that describes the rate and quantity of air flow throughout a prolonged expiration. Assessment of exhaled nitric oxide, a marker of the inflammation of asthma, and also carbon monoxide, a marker of cigarette smoking and carbon monoxide poisoning, may be performed. Both these tests also require the patient to exhale into a machine.
Serum samples can be used to examine for antigens of infectious agents and for antibodies to confirm the presence of infection. Certain antibodies can also indicate the tendency to allergy, which is common in asthmatics.
Blood tests can also reveal other markers of chronic respiratory disease such as autoantibodies in connective tissue diseases and anticholinesterase levels in sarcoidosis.
In the investigation of lower respiratory tract disease, a sample of arterial blood is drawn from the radial artery to measure the concentration of oxygen and carbon dioxide in the blood.
Chest X-ray imaging
This test is performed on all patients with suspected lower respiratory tract disease. Most serious disease, such as pneumonia, cancer, emphysema and lung fibrosis, will show characteristic changes on a chest X-ray image. However, in asthma, even when severe, the chest X-ray image usually appears normal.
Computed tomography (CT) scan
This test is most commonly used to assess the size and spread of lung cancer. A CT scan will reveal not only the lung tissue, but also the lymph nodes deep within the chest. It can also indicate changes caused by other chronic lung diseases such as pulmonary fibrosis and asbestosis.
Figure 3.3b-I shows a CT scan of the lungs in a patient with advanced lung cancer. This is a slice of the upper chest presented as if the patient is lying on their back with their feet facing the viewer. The white structures are bones, and the sternum, one vertebral body, some ribs and the scapulae are visible. The very black areas are regions of normal air spaces in the lungs. The cancer is clearly seen as a gray shadow invading the normal lung tissue.
Figure 3.3b-I A CT scan of the lung indicating a large area of cancerous tissue (arrow)
The less-invasive technique of magnetic resonance imaging (MRI) is less valuable in imaging of the tissues of the lung because the respiratory movements affect the quality of the images.
This invasive test involves the passage of a flexible telescope into the wider air passages of a sedated patient. The tube can be inserted as far as the larger bronchioles. Tumors can be seen directly by means of this technique.
Alternatively, salt water can be squirted down the tip of the tube to retrieve cells from the deeper parts of the lungs in cases of possible infection or cancer when sputum does not reveal any features of disease. This technique is known as broncho-alveolar lavage.
Biopsy of the lung tissue
Biopsy involves the removal of a piece of lung tissue for examination under the microscope. The biopsy can be taken from the bronchi or bronchioles through the bronchoscope. Biopsy of the pleura can be taken through a small incision in the skin overlying a gap between the ribs. Sometimes a thoracic surgeon is required to open up the chest to remove tissue from deep in the chest.
Biopsy is most commonly used to confirm the diagnosis of cancer, but can also be used when sarcoidosis or infection is suspected, but cannot be detected by any other means.
Fluid can also be drawn from between the pleura by means of a syringe needle inserted between the ribs into the space. This is used only in those conditions that have caused fluid to accumulate in this space, known as pleural effusion. Such conditions include cancer of the bronchus, pneumonia and pulmonary edema.
Radioisotope scanning may be used to examine for possible blockages to blood flow in the lungs, usually a result of blood clot emboli. The blood is injected with a safe radioactive marker with a very short half-life (i.e. its activity declines to insignificant levels very rapidly). Defects in blood perfusion of the lungs can then be revealed by means of scanning the lungs for radioactivity.
3.3c Diseases of the upper respiratory tract
Minor diseases of the upper parts of the respiratory tract such as coughs, colds and flu are a well-recognized part of normal life. Conditions that affect the structures progressively further down the respiratory tract, such as the tonsils, larynx and trachea, are seen in conventional medicine as more significant conditions. Nevertheless, on the whole, most acute conditions of the upper half of the respiratory tract are relatively benign.
The conditions of the upper respiratory tract studied in this section are:
•Acute infections of the upper respiratory tract:
–the common cold
–tonsillitis and pharyngitis
–glandular fever (infectious mononucleosis)
–laryngitis, tracheitis and croup
•Cancer of the larynx (see also Chapter 2.3).
Acute infections of the upper respiratory tract
With the exception of some forms of tonsillitis and pharyngitis and the childhood infection acute epiglottitis, all the common infections of the upper respiratory tract are initially caused by viruses. A wide range of viruses has been identified to affect the respiratory epithelial cells. Viruses tend to enter the upper respiratory tract through inhalation of infected droplets of moisture. The inhaled virus is able to penetrate and damage the cells, and this leads to inflammation (redness and swelling) and the production of sometimes profuse watery secretions. Fever is a common symptom of these infections, although frequently it is mild in nature. Breathlessness (which is significant if respiration rises to over 30 breaths per minute in adults) is not a feature of upper respiratory conditions. Breathlessness suggests a more serious lower respiratory condition or obstruction to the upper airways, and if severe merits same-day referral for a medical opinion.
The different syndromes that result from upper respiratory infection seem to be dependent on the characteristics of the virus. Some primarily affect the throat and the nasal lining, leading to the symptoms of the common cold, whereas others tend to affect lower structures, causing tonsillitis or laryngitis, for example. The evidence for this is that a virus that is “going around” will tend to cause the same range of symptoms in most people who contract the infection.
Usually, viral infections of the upper respiratory tract are short-lived. In some people the infections can progress to affect further regions of the respiratory system, including the lower respiratory tract. In these cases, it is often believed that a further bacterial infection has arisen in the region of the already damaged respiratory epithelium. It is often the case that it is the healthy bacteria, which usually reside harmlessly in the lining of the upper respiratory tract, that cause these complications. Therefore, these sorts of deeper bacterial infections are not usually contagious. This complication of bacterial infection is recognized to be more likely in people who are susceptible due to some form of chronic ill health. As long as upper respiratory conditions last for less than five days there is usually no need for medical referral, except in the case of infants or frail individuals.
The treatment for all minor viral upper respiratory conditions needs be supportive only, as the antiviral drugs currently available are expensive, carry risks and only shorten rather than eliminate the symptoms of illness in healthy individuals. For this reason, the use of these drugs in the National Health Service (NHS) is restricted according to the UK National Institute for Health and Care Excellence (NICE) guidance (2009),54 being given only in cases of influenza in vulnerable individuals. Common treatment approaches recommended by doctors include aspirin and paracetamol to reduce pain and fever, plenty of fluids to counteract fluid loss through fever, keeping warm and letting the body rest.
There is no doubt that smokers are more prone to severe forms of upper respiratory tract infections. It is also recognized that atmospheric pollution results in increased rates of severe respiratory infections. Both these factors reduce the health of the respiratory epithelium so that it is less well equipped to deal with minor infections. Smoking, in particular, is known to damage the action of the cilia in the respiratory epithelium and also to cause a change in the production of the mucus so that it becomes much thicker and thus resistant to clearance from the air passages.
The accumulation of thick and sticky mucus that results when a smoker develops a viral respiratory infection is much more likely to become further infected by bacteria and to result in a persistent phlegmy infection.
The cough and profuse phlegm familiar to people who have recently stopped smoking is a healthy sign. It is a result of the recovery of the cilia, which are then able to clear accumulated toxins and mucus from the lower parts of the respiratory tract.
The common cold
The common cold virus affects the nose and pharynx (throat), leading to sore throat, stuffy and runny nose, and watery eyes. The secretions are usually clear. Fever is slight or absent. Simple treatments for the common cold include vitamin C and zinc preparations and steam inhalations to loosen secretions. Eucalyptus and menthol oils can be a helpful addition to a steam inhalation, and these aromatic compounds are also commonly found in proprietary cough sweets and medicines. Aspirin or paracetamol may be taken to relieve the discomfort of sore throat and to reduce fever.
Decongestant preparations that act by constriction of the blood vessels of the nose are not generally considered to be of great benefit. However, they are freely available as proprietary medications in the form of tablets or nasal sprays. Some of these contain drugs similar in action to the chemical ephedrine. Decongestants reduce the swelling of the nasal lining and reduce the secretions. However, these are conventionally recognized to be suppressive, and so the symptoms may recur in a more pronounced form when the drug wears off. Examples of decongestant medication include Vicks Sinex and Sudafed nasal sprays.
Some cold preparations available from the chemist contain mild sedatives, which are intended to help by allowing the person to rest.
A common cold is not seen to be serious in conventional medicine except in people who have a risk of further infection due to ongoing chronic disease or immunodeficiency.
Information box 3.3c-I
The common cold: comments from a Chinese medicine perspective
In Chinese medicine, the symptoms of the common cold are described as an Invasion of Wind Heat or Wind Cold (and occasionally Wind Damp Heat or Wind Dry Heat) on the Exterior. They are believed to occur because of the relative weakness of Wei Qi compared to the strength of the Pathogenic Factor. As such, if treated in its early stages by releasing the Exterior and Clearing Wind, the development of a common cold is believed to be preventable.
According to the Six Levels theory in the Shang Han Lun (On Cold Damage: Zhang Zhongjing, circa 200 CE), a common cold due to Wind Cold is at the most superficial Greater Yang (Tai Yang) level. According to the Four Levels theory from the Discussion of Warm Diseases (Ye Tianshi, circa 1710 CE), a common cold due to Wind Heat is at the most superficial Defensive (Wei) Qi Level.55
In contrast to conventional medicine, an Invasion of Wind Heat or Wind Cold is taken very seriously in Chinese medicine, as there is a risk it may descend to deeper energetic levels and change into Heat unless appropriate care and treatment is given.
From the integrated perspective of infectious disease introduced in Section 2.4d, the infectious viruses might be seen as the source of a Pathogenic Factor of external origin, whereas many bacterial complications of these infections might be interpreted as the result of additional Pathogenic Factors of internal origin. This is comparable to the concept in Chinese medicine that superficial invasions of Wind Heat or Wind Cold can progress to deeper levels in people with Depleted Qi, and so fits in with the idea that in these cases the Pathogenic Factor is of internal origin.