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The lungs are made of elastic tissue filled with interlacing networks of tubes and sacs carrying air, and with blood vessels carrying blood. The bronchi, which bring air to the lungs, branch out within the lungs into many smaller tubes, the bronchioles, which culminate in clusters of tiny air sacs called alveoli, whose total runs into millions. The alveoli are surrounded by a network of capillaries. Through the thin membranes of the capillaries, the air and blood make their exchange of oxygen and carbon dioxide.
The lungs are divided into lobes, the left lung having two (the left upper lobe and the left lower lobe) and the right having three (the right upper lobe, the right middle lobe, and the right lower lobe); these are further subdivided into bronchopulmonary segments, of which there are about 20. Protecting each lung is the pleura, a two-layered membrane that envelops the lung and contains lubricating fluid between its inner and outer layers.
Deflation of the lungs is chiefly a passive maneuver. The major muscles involved in exhalation are the abdominal muscle group. As these muscles contract, they depress the lower ribs, and, through an increase in abdominal pressure, move the diaphragm upward.
As the lungs are compressed and distended by the respiratory muscles, the pressure within the alveoli (intra-alveolar pressure) rises and falls. During inhalation the pressure becomes slightly negative (−3 mm Hg) in relation to atmospheric pressure. During exhalation the intra-alveolar pressure rises to approximately +3 mm Hg. The effect of negative pressure within the alveoli is to cause air under atmospheric pressure to flow into the lungs (inhalation). The condition of positive pressure creates the opposite effect, causing air to flow outward (exhalation).
The lungs are surrounded by an airtight compartment, the pleural space within the pleural membrane. The intrapleural pressure is less than atmospheric pressure and is expressed as negative pressure. Normally the intrapleural pressure is about −4 mm Hg. When the lungs are fully expanded this pressure may be as great as −9 mm Hg. Under normal conditions, however, the intrapleural pressure fluctuates between −4 and −6 mm Hg.
If anything should penetrate the walls of the pleura, the negative pressure is lost as air rushes into the pleural cavity in response to atmospheric pressure. This condition is called pneumothorax. The walls of the alveoli also must remain intact in order to maintain normal intrapleural pressure. If a lesion causes a break in the alveolar membranes, air enters the pleural cavity through the break and produces pneumothorax. Relief of pneumothorax and collapse of the lung from accumulations of either air or fluids within the pleural space may be provided by aspiration of the air or fluid from the thoracic cavity (thoracentesis) or by insertion of chest tubes to provide for a gradual reexpansion of the lung. (Specific tests to determine pulmonary volume and capacities are discussed under pulmonary function tests.)
The first symptoms include a dry cough and chest pain. Later these may be followed by fever, chills, productive cough, headache, perspiration, foul-smelling sputum, and sometimes dyspnea. If the abscess is a complication of pneumonia, the symptoms tend to be moderated to an exaggeration of the pneumonia symptoms.
When a lung abscess forms, it is in the acute stage and treatment with antibiotics usually is effective. postural drainage may be prescribed to assist in drainage of exudate from lungs and bronchioles. In most cases, this treatment produces a cure. If the abscess becomes chronic, surgery may be necessary and usually involves removal of the portion of the lung containing the abscess.
A study based on autopsies of the lungs of individuals who had died from many varied causes, but whose smoking history was known, showed that unrecognized cancer and precancerous changes in tissue were numerous among smokers and rare among nonsmokers. These findings led the Surgeon General of the United States to appoint an investigative committee, which ultimately issued a report stating that “cigarette smoking is a health hazard of sufficient importance in the United States to warrant appropriate action.”
Since the factors causing lung cancer act slowly and may produce a tumor near the periphery of the lung, early symptoms are vague or may not appear at all, and nearly a third of the cases are in an advanced stage when they are discovered. The earliest and most common symptom is a cough. Dry at first, this cough later produces sputum, which eventually becomes blood-streaked. An isolated persistent wheeze in the chest is frequently a symptom and indicates a partial obstruction in a bronchus. Chest pains, weakness, and loss of weight are later symptoms, as is dyspnea.
Diagnosis depends on a careful physical examination, including a chest x-ray. If a suspicious density is seen on the x-ray, samples of sputum will be examined microscopically for the presence of malignant cells. bronchoscopy is also done, and at the same time a specimen for biopsy can be obtained or the bronchial secretions can be washed out and the cells stained and examined.
When examination indicates lung cancer, prompt treatment is essential. This may involve the surgical removal of the lobe of the lung containing the cancer or of an entire lung if the malignant cells have spread. A significant number of persons affected by lung cancer can be cured by such operations if the surgery is performed in time. In some cases of widespread involvement surgery is not possible; these patients are treated with radiation therapy and antineoplastic drugs.
Carcinogens that can trigger lung cancer must be avoided and, when possible, eliminated. Mine workers should take adequate precautions to avoid inhaling harmful dusts. Public health authorities and industry must act more effectively to control air pollution. The most important step toward protection against lung cancer is elimination of cigarette smoking. State and local units of the American Lung Association are excellent sources of information about lung disease and its prevention.
Lung cancer clinical guidelines have been published in both the United States and Canada. In Canada they are available at the web site of Cancer Care Ontario, http://www.cancercare.on.ca. and in the United States they are available at the web site of the National Guideline Clearinghouse, http://www.guideline.gov.
Drin·ker res·pi·ra·tor(dringk'ĕr res'pir-ā'tŏr)
Synonym(s): iron lung.
The lungs are connected with the pharynx through the trachea and larynx. The base of each lung rests on the diaphragm, and each lung apex rises from 2.5 to 5 cm above the sternal end of the first rib, the collarbone, supported by its attachment to the hilum or root structures. The lungs include the lobes, lobules, bronchi, bronchioles, alveoli or air sacs, and pleural covering.
The right lung has three lobes and the left two. In men, the right lung weighs approx. 625 g, the left 570 g. The lungs contain 300,000,000 alveoli and their respiratory surface is about 70 sq m. Respirations per minute are 12 to 20 in an adult. The total capacity of the lung varies from 3.6 to 9.4 L in men and 2.5 to 6.9 L in women.
The left lung has an indentation, called the cardiac depression, for the normal placement of the heart. Behind this is the hilum, through which the blood vessels, lymphatics, and bronchi enter and leave the lung.
Air travels from the nasal passages to the pharynx, larynx, and trachea. Two primary bronchi, one on each side, extend from the trachea. The primary bronchi divide into secondary bronchi, one for each of five lobes. These further divide into a great number of smaller bronchioles. The pattern of distribution of these into the segments of each lobe is important in pulmonary and thoracic surgery. There are about 10 bronchopulmonary segments in the right lung and eight in the left, the actual number varying. There are 50 to 80 terminal bronchioles in each lobe. Each of these divides into two respiratory bronchioles, which in turn divide to form two to 11 alveolar ducts. The alveolar sacs and alveoli arise from these ducts. The spaces between the alveolar sacs and alveoli are called atria.
In the alveolus, blood and inspired air are separated only by the cell of the alveolus and that of the pulmonary capillary. This respiratory membrane is thin (0.07 to 2.0 µm) and permits oxygen to diffuse into the blood and carbon dioxide to diffuse from the blood to the air.
The lungs are innervated by parasympathetic fibers via the vagus nerve and sympathetic fibers from the anterior and posterior pulmonary plexuses to the smooth muscle in the walls of the bronchial tree.
The bronchial arteries and veins circulate blood to the bronchial tree. The pulmonary arteries and veins circulate the blood involved in gas exchange.
The primary purpose of the lung is to bring air and blood into intimate contact so that oxygen can be added to the blood and carbon dioxide removed from it. This is achieved by two pumping systems, one moving a gas and the other a liquid. The blood and air are brought together so closely that only approx. 1 µm (10-6 m) of tissue separates them. The volume of the pulmonary capillary circulation is 150 ml, but this is spread out over a surface area of approx. 750 sq ft (69.68 sq m). This capillary surface area surrounds 300 million air sacs called alveoli. The blood that is low in oxygen but high in carbon dioxide is in contact with the air that is high in oxygen and low in carbon dioxide for less than 1 second. See: respiratory defense mechanism
Inspection: The examiner determines the respiratory rate by unobtrusively watching the patient's chest rise and fall and counting the number of breaths per minute. In adults a normal respiratory rate at rest is about 12 breaths per minute. While counting the respiratory rate, the examiner can observe other breathing characteristics. Dyspneic patients breathe rapidly, often laboring to draw breath even when at rest. Retractions of the intercostal and supraclavicular spaces are visible during inspiration. Sleep apnea is characterized by episodes of stalled breathing followed by periods of respiratory compensation. Regular slow breathing is normal.
Palpation: In health, the chest and lung transmit a vibration, called fremitus, during speech. Fremitus abnormalities may be felt in chronic obstructive lung diseases or obesity, in which the vibration is diminished, and in pneumonia, in which it is increased over the infected lobe.
Percussion: Tapping on the chest wall over healthy lung results in a hollow resonant sound. The hollow character of the resonance sometimes is exaggerated in emphysematous lungs or in pneumothorax, and muffled by pleural effusions or pulmonary consolidation.
Normal breath sounds: In the healthy person, breath sounds are low-pitched and have a frequency of 200 to 400 cycles per second (cps); frequency rarely exceeds 500 cps. These sounds are called vesicular breath sounds when heard over the lungs. They are produced by air passing in and out of the airways.
Bronchial and tracheal breath sounds: These are higher-pitched and louder than vesicular sounds, and are produced by air passing over the walls of the bronchi and trachea. These sounds are normally heard only over the bronchi and trachea.
Amphoric and cavernous breathing:These two nearly identical sounds are loud, with a prolonged, hollow expiration. The pitch of amphoric breathing is slightly higher than that of the cavernous type, and may be imitated by blowing over the mouth of an empty jar. It is heard in bronchiectatic cavities or pneumothorax when the opening to the lung is patulous; in the consolidation area near a large bronchus; and sometimes over a lung compressed by a moderate effusion.
Harsh inspiratory sounds are typical of stridor, a medical emergency. Expirations that are prolonged and musical are characteristic of wheezing.
Friction: This sound is produced by the rubbing together of roughened pleural surfaces. It may be heard in both inspiration and expiration. Friction often resembles crackle, but is more superficial and localized than the latter and is not modified by cough or deep inspiration.
Metallic tinkling: A silvery bell-like sound heard at intervals over a hydropneumothorax or large cavity. Speaking, coughing, and deep breathing usually induce this sound. It must not be confused with a similar sound produced by liquids in the stomach.
Crackles: Abnormal bubbling sounds heard in air cells or bronchi.
Succussion-splash or hippocratic succussion: A splashing sound produced by the presence of air and liquid in the chest. It may be elicited by gently shaking the patient during auscultation. This sound nearly always indicates either a hydropneumothorax or a pyopneumothorax, although it has also been detected over very large cavities. The presence of air and liquid in the stomach produces similar sounds.