Pathophysiology - 09 Respiratory Disorders.pdf

PATHOPHYSIOLOGY • LECTURE 9 - THE RESPIRATORY SYSTEM UPPER RESPIRATORY DISEASES THE COMMON COLD • • • More than 200 strains of viruses are capable of causing this disease. Metapneumovirus, within the paramyxovirus family of viruses, has recently been described as a major virus causing adult colds, and it acts very severely on infants when first encountered. In the weak or elderly this agent is taken cautiously as well. Unlike many other diseases, having had a cold provides no immunity. Another strain of virus is always ready to attack. Moreover, the common cold is relatively contagious. Symptoms, Etiology, and Treatment o A cold is an acute inflammation of the mucous membrane lining the upper respiratory tract. The initial stuffed-up feeling, is caused by the swelling of the mucous membrane, which narrows the air passageway. Copious secretion of mucus follows acute inflammation. o No known cure for the common cold. Beyond bed rest, cold symptoms can be treated by taking aspirin for fever and antihistamines for relieving congestion. o Coughing helps clear irritants or excessive mucus in the nasal and throat areas, and sometimes this abrupt flow of air races by at speeds approaching 200 mph. Occasionally secondary infections occur. The infection may be treated with antibiotics when caused by bacteria, and therefore cold sufferers may be on antibiotics for a “cold.” Etiology, Symptoms, Treatment o Viruses, allergens, bacteria o Environmental conditions ▪ barometric pressure, airplane flight, swimming or diving activities, & perhaps stale or contaminated indoor air like in “sick building syndrome.” ▪ tooth extraction or dental work, abscesses, and allergens. Sinusitis, an infection of the sinuses, can be caused by nasal congestion blocking sinus drainage. o When the mucous membranes lining these cavities are inflamed the results are headache above or below the eye orbit, occasionally pain in the cheeks and upper teeth and a general “stuffiness” felt behind or within the nasal cavity. o Depending on the cause, susceptibility, and severity of a case of sinusitis, it may take 3 to 4 weeks to resolve. o A thick viscous discharge varying in yellowish to green color may suggest a bacterial invasion has occurred. Sinusitis may be confirmed by physical observation that may include x-ray and endoscopic sinuscopy plus patient history. Discharge samples may be sent to the laboratory to confirm or rule out bacterial invasion or other agents. o Treatment: decongestants and antihistamines, antibiotics, surgery NASAL POLYPS • • • • • Nasal polyps are noncancerous growths within the nose or sinus passageway. The exact cause of these growths is unknown. Certain chemicals found within these polyps suggest that they may be instrumental in causing the extra tissue formations. Typically, nasal polyps form along with a sensitivity or allergic response to aspirin and some aspirin-like substitutes. Individuals with asthma and chronic rhinitis (nasal inflammation) are susceptible, as are children with cystic fibrosis. Large polyps cause nasal drainage, interfere with smell capability, and, on rare occasions may be linked to obstructive sleep apnea (OSA). Treatment primarily suggests surgery, but only if the polyps are troublesome. Nasal sprays with cortisone-like drugs are used for allergy control. However, even if the surgery clears the passageway, it may not prevent the uncertain cause of these internal nasal lumps. OBSTRUCTIVE SLEEP APNEA SINUSES AND SINUSITIS • • • In the United States, approximately one person in seven has sinus problems at a cost of more than a billion dollars per year. The air filled spaces provide a reduced weight for the skull and contribute to nasal tone of the voice. Paranasal sinuses drain into the nasal cavity. These cavities are named by the skull bone in which they are found: frontal, ethmoid, maxillary, and sphenoid. In sinusitis, the inflammation of the mucous membranes that line the cavity causes a sensation of pressure, pain, and often a headache. Children have a tendency toward ethmoid sinus inflammation more commonly than do adults. • • • • • • The most common sleep disorder The apnea is noted by cessation of breathing during the night due to a non-foreign obstruction like an inhaled object, but caused by enlarged parts (e.g., nasal polyps or uvula) or displaced parts like deviated septum or fatty bodies. Usually occurs in middle age, and in overweight males. Individuals awake tired, without energy, and feel drowsy most of the day while functioning at low capacity. Four or five episodes of sleep apnea per hour is significant. Twenty episodes per hour is severe; some people experience 100–500 apneas in a single night. Syndrome: Symptoms and Treatment PATHOPHY • 1 o o o o o Obstructive apnea causes heavy, long, and loud snoring and snorting. Three fourths of the time researchers have found that during this interruption, decreased blood flow to the brain has occurred. With upper airways blocked, lungs do not fill properly, which creates a pressure in the chest that compresses the heart, and therefore reduces blood flow. The potential for cerebral stroke is increased, especially in moderate and severe apnea cases. Causes and treatment for OSA were outlined in the previous section. Treatment depends on the particular case, but if weight is a problem it may be dealt with without fanfare. If sinuses or nasal cavities are misshaped or blocked they need repair. Some patients find relief with pharyngoplasty—trimming of the uvula (superior mid throat flap) to prevent blockage of breathing passageway. o • HAY FEVER • • • • • • Also called seasonal allergic rhinitis, it is characterized by sensitivity to airborne allergens, especially from pollens of ragweed and grasses. Respiratory mucosa secrete excessive mucus causing a runny nose and congestion. Mucosal surfaces of the eyes also react to the allergens causing redness, watery secretions, and itching. Because the release of histamine causes these unpleasant effects, a substance that counteracts its action, an antihistamine, may give relief. Newer medications like Flonase may help sufferers on a short-term basis. Many hay fever sufferers take allergy injections to desensitize them to pollen or other allergens. o Desensitizing works by administering small doses of antigen and gradually increasing the dosage, allowing the person to produce antibodies against it. It is hoped that these antibodies can inactivate the pollen before it interacts with the nasal mucosa. TONSILLITIS, PHARYNGITIS, LARYNGITIS • • • • These upper respiratory airway structures can become infected with bacteria, viruses, or other pathogens. Infections of these tissues lead to difficulty swallowing, and redness and pain in the throat. Tonsillitis o The tonsils are masses of lymphatic tissue located in the mucous membranes of the fauces and the oral pharynx that protect the throat from infection. o Infected tonsils may swell and become painful, making swallowing very difficult. When persistent bouts of infection continue, it may call for surgical measures (tonsillectomy), especially when the middle ear (otitis media) becomes inflamed. Pharyngitis o An inflammation of the pharynx characterized by pain in the throat. Foreign objects, hot liquids, or spicy foods may contribute to short-term pharyngitis. Just breathing through the mouth, due to stuffiness, or falling asleep with an open mouth may cause a brief discomfort caused by excessive drying and exposure. o Strep throat, a pharyngitis caused by streptococci, is common, resulting in a red, purulent throat. o The presence of bacteria in the throat can be confirmed by a throat culture or a rapid immunological test that can be performed in the physician’s office. o Antibiotics control the infection. Laryngitis o An inflammation of the larynx or voice box, is characterized by hoarseness and aphonia. A “lost voice” may be caused by bacteria or viruses or perhaps fungi, but it can also stem from allergies, overuse of the voice, as experienced by singers, politicians, and auctioneers, and other factors. o For bacterial infections, antibiotics are used. o Laryngitis, which is one form of the “croup,” can also be treated by resting the voice, drinking fluids, and steam inhalations. INFLUENZA • • • • • • A viral infection of the upper respiratory system. The onset of the disease is sudden. The individual experiences chills and a fever, cough, sore throat, and runny nose. Chest pains, muscular aching, and gastrointestinal disorders may also be symptoms. Many different strains of viruses causing influenza are known. Unfortunately, immunity for one strain does not protect against another strain. There is a broad range in the severity of flu cases. It can be very mild, or it can lead to pneumonia and be lifethreatening. Influenza is particularly serious in the elderly and chronically ill. The virus can destroy the respiratory epithelium, a strong line of defense against bacterial invasion. With the loss of the protective epithelium, bacterial infection can invade any part of the respiratory tract. Pneumococci, streptococci, and staphylococci are all capable of causing pneumonia in patients with severe influenza. Treatment of Influenza o There is no medication that cures influenza. o Sometimes antibiotics are prescribed to ward off secondary bacterial infection. o Bed rest, fluids, and aspirin to reduce fever are the usual treatments. o Flu vaccines are made available before the onset of the season, typically in October and November, and are recommended for those considered at high risk; elderly and respiratory compromised. Unfortunately, these shots do not give immunity for all strains of the influenza virus. LOWER RESPIRATORY DISEASES CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD) • Chronic obstructive lung disease (COLD), includes a number of conditions in which the exchange of respiratory gasses is ineffective. It includes chronic bronchitis, emphysema, and chronic asthma. BRONCHITIS • Inflammation of bronchi, w/c may be acute or chronic. PATHOPHY • 2 • • • • The mucous membrane lining the bronchi becomes swollen and red, the typical inflammatory response. Irritants such as industrial fumes, automobile exhaust, viruses, or bacteria can cause acute bronchitis. Acute Bronchitis o Most serious in small children, the chronically ill, and the elderly. o Tiny bronchioles of children can become easily obstructed. The elderly or chronically ill are likely to develop a secondary infection, such as pneumonia. o Acute bronchitis is characterized by chest pains, dyspnea, cough, fever, and sometimes chills. o The sputum coughed up may contain pus. o Depending on the organism causing the bronchitis, antibiotics may be administered. Viruses do not respond to antibiotics, but vapors, sprays, and cough medicines may give relief. Chronic Bronchitis o Indicated by repeated attacks of acute bronchitis and coughing with sputum production, lasting for at least 3 months for 2 consecutive years. o Symptoms are persistent. o Chronic bronchitis may be a complication of another respiratory infection, or can result from long-term exposure to air pollutants or cigarette smoke. It is more common in middle-aged men than in women. Symptoms of Bronchitis o Symptoms include excessive secretion of mucus from the mucous glands of the bronchial mucosa (lining). The mucous glands hypertrophy, and the mucosa itself is thickened and inflamed. o The interference in the air passageway caused by the swelling and mucus reduces the person’s oxygen level. o Hypoxia, an insufficient oxygenation of the tissues, results. Poor drainage of the mucus sets the stage for bacterial infection. Parts of the respiratory tract can become necrotic, and fibrous scarring follows. o Chronic bronchitis is aggravated by other respiratory diseases or environmental factors. o The symptoms can be treated with antibiotics and moist vapors to ease the breathing. A cigarette smoker should quit smoking, and clean air environments should be sought at all times. BRONCHIAL ASTHMA • • • • • Characterized by hypersensitivity to various allergens like dust, mold, pollen, animal dander, and various foods Eighty percent of children with asthma and fifty percent of adult asthmatics have allergies. The allergens trigger constriction of smooth muscle in the walls of the bronchi, narrowing the lumen of the tubes. The spasm is a sustained contraction of the musculature, making breathing, particularly expiration, very difficult. The mucous membrane becomes swollen with fluid, also narrowing the lumen. Excessive secretion of mucus adds to the obstruction. Stale air becomes trapped, which decreases the amount of fresh air that can enter the lungs. The wheezing sound results from air passing through the narrowed tubes. Psychogenic factors such as anxiety are frequently associated with an asthma attack. Tense situation or emotional experience can trigger an attack. • • • • Other nonallergic causes are overexertion, infection, or bronchitis. Exposure of the bronchial mucosa to irritants such as cigarette smoke, aerosol sprays, or perfume can also trigger an attack. There is no cure for asthma, but attacks may become less severe with age. It is important to identify the offending allergens and avoid contact with them as much as possible. Because overexertion may be involved, it is important for the athlete to take some extra time to “warm up” and get adjusted to the situation before participating in physical activities and sports. Normal lung alveoli magnified 25X • Emphysema. Note enlarged and fused alveoli in emphysema. • Treatment and Prognosis of Asthma o Medication and allergy shots can reduce the incidence or severity of asthma attacks. o To counteract an ongoing attack, substances that dilate the bronchi are effective. Ephedrine sprays and epinephrine (adrenalin) injections are often effective. o Bronchodilators like albuterol and metaproterenol are sometimes prescribed. o Cortisone-like drugs and antihistamines are sometimes used, but these carry a risk of side effects. o The most severe form of an asthma attack is called status asthmaticus, in which the patient fails to respond to the usual treatment. A procedure as drastic as a tracheotomy, an opening of the trachea surgically, may be required. If not treated, status asthmaticus may end in respiratory failure and death. o Asthma kills at least 15 people daily in the United States, according to the American Lung Association. o The disease is also increasing across the country (up 4% in 2002). About 4 million Americans have asthma and it affects all ages, but particularly youngsters. Perhaps because of new building designs since the 1970’s and more activities occurring indoors, asthma has become a major concern for the medical PATHOPHY • 3 community. Education offers considerable relief psychologically and physically. o EMPHYSEMA • • • • • • • • A crippling and debilitating (weakening) disease with chronic lung obstruction and destruction The word emphysema means inflation. The lungs become filled with air that is high in carbon dioxide. This air cannot be adequately exhaled to allow oxygen to enter. The person experiences a suffocating feeling and great distress from the inability to breathe. Severe pain accompanies the difficult breathing. The cause of emphysema is not known, but it is most frequently associated with heavy cigarette smoking. An inherited form has been identified also. Individuals with a deficiency in alpha-1-antitrypsin are prone to alveolar destruction characteristic of emphysema. Air pollution and long-term exposure to irritants of the respiratory tract also seem to be factors of its etiology. Emphysema is a frequent complication of chronic bronchitis. Whatever the cause, the alveolar walls break down, adjacent alveoli fuse, and the lungs lose their elasticity. Signs and Symptoms of Emphysema o Typically, a person with emphysema has an increased rate of breathing and a greater than normal expansion of the chest. This hyperventilating clears out carbon dioxide that is building up internally because of poor lung functioning. o Permanent expansion of the chest (“barrel” chest); abnormal respiratory sounds called rales o Right-sided heart failure or cyanosis because of marked hypoxemia o Hypoventilation reduces oxygenation o Emphysema can last for many years, causing irreversible damage to the lungs. As in any serious disease, complications often develop. With the breakdown of alveolar walls, the surrounding blood capillaries are damaged. o This interference with circulation in the lungs can lead to an obstruction of the pulmonary artery. The large air sacs, formed by the fusion of the alveoli, tend to rupture. This allows air into the pleural cavity, the space between the lungs and the chest wall. Air in this space can cause the lung to collapse. Diagnosis and Treatment of Emphysema o Early detection of emphysema can slow its progression. Symptoms such as a chronic cough (often called smoker’s cough), shortness of breath, and abnormally rapid breathing indicate a respiratory disease, and a physician should be consulted. o A spirometer measures the movement of air in and out of the lungs o X-rays do not show emphysema in the early stages. o Treatment involves eliminating the source of the irritation. A smoker will be told to quit smoking and to avoid polluted air containing smoke, fumes, and irritating dust. The patient should observe ozone warnings and limit outdoor activity when the ozone level is high. o Medications that clear mucus from the lungs help prevent infection. Some medications give relief from the feeling of not being able to breathe, such as albuterol or metaproterenol. Physical therapy is sometimes helpful in teaching individuals to use all the possible muscles for respiration in the abdomen and chest wall. PNEUMONIA • • • • • Acute inflammation of the lungs in which air spaces in the lungs become filled with an inflammatory exudate. Oxygen exchange is impaired, causing difficulty breathing. Fever, chest pain, and a productive cough accompany this disease. A chest x-ray and analysis of sputum can diagnose pneumonia and determine its cause. Pneumonia can be caused by a variety of microorganisms, and it may affect different areas of the lungs. A) Bronchopneumonia with localized pattern. (B) lobar pneumonia with a diffuse pattern within the lobe. ( C ) interstitial pneumonia typically diffuse and bilateral. • • • • Lobar Pneumonia o Lobar pneumonia is inflammation of a section, often an entire lobe, of the lung. It is most often caused by the pneumococcus bacterium, Streptococcus pneumoniae. o This bacterium is carried in the respiratory passages of many people, but it can infect the lungs under optimal conditions. o People with other disease processes, chronic bronchitis, or weakened immune systems are most susceptible. Treatment includes use of antibiotics, such as penicillin. Bronchopneumonia o Obstruction of the small bronchi o Due to infection or by aspirated gastric contents o Diffuse pattern of inflammation on x-ray o This type of pneumonia is more common in debilitated patients who are bedridden from other pathology. Predisposing causes of bronchopneumonia are: ▪ Chronic bronchitis ▪ Measles or whooping cough ▪ Bronchiectasis ▪ Old age ▪ Cancer Primary Atypical Pneumonia o Caused by a variety of microorganisms, including viruses and unusual bacteria called Mycoplasma pneumoniae. o Interstitial pneumonia, common in viral pneumonia, is characterized by the diffuse pattern on x-ray o The disease is more common among adolescents and young adults. Legionnaires’ Disease o Caused by the bacterium, Legionella pneumophila o Characterized by flu-like symptoms, which sets it apart from other pneumonias. This is a serious and PATHOPHY • 4 • potentially fatal disease, and sputum cultures and chest x-rays can differentiate it from other infections. o The disease is acquired by inhaling droplets contaminated with the bacteria from air conditioning cooling systems, humidifiers, and other equipment that produces aerosol water droplets. o The antibiotic erythromycin is the treatment of choice. Secondary Pneumonia o Can develop as a secondary disorder from other diseases that weaken lungs or body’s immune system o Graft recipients and immunocompromised people, especially HIV/AIDS patients, are susceptible to pneumonia caused by unusual infectious agents like the fungus, Pneumocystis carinii, and the fungus, Cryptococcus neoformans. o Postoperative patients, bedridden patients, and those with chronic respiratory illness may lack the ability to clear their lungs effectively and are at risk for developing pneumonia. o The most unfavorable secondary pneumonia is the one acquired as a complication of influenza. It was responsible for many of the 20 million deaths in the Spanish Flu epidemic of 1918–1919. This was a devastating disease that apparently started in the United States, was transported to (and from) Europe by American soldiers and always involved double (both lungs) pneumonia. Today, influenza still causes many cases of pneumonia, and the flu vaccine is recommended for persons at risk. o • PLEURISY • • • Inflammation of pleural membranes that occurs as a complication of various lung diseases, like pneumonia or tuberculosis. May also develop from an injury or tumor formation. Pleurisy is extremely painful; a sharp, stabbing pain accompanies each inspiration. The pain may stem from excessive or insufficient pleural fluid, or pus/blood in the lungs. It is treated with antibiotics, heat applications, and bed rest. During this period, a person may have no symptoms. A secondary infection occurs when the person is infected again or when the bacteria escape the walled-off lesions in the lungs. o The bacteria may spread this way when the person’s resistance is reduced because of stress, infection, malnutrition, or immuno-deficiency. o During the secondary infection, leukocytes now recognize the bacteria and mount an attack that leads to greater necrosis and destruction of lung tissue. o Necrotic tissue, blood, and bacteria may be coughed up. The bacteria may spread to other organs like the brain, kidney, and bones. Persons in the secondary stage of the disease also lose weight and become cachectic; this is the basis for the classic name for tuberculosis, consumption. Screening and Treatment of Tuberculosis o The treatment for tuberculosis involves antibiotics specially designed for Mycobacterium species. These drugs may include rifampin, isoniazid, ethambutol, or others. The drugs must be taken over an extended period of time for as much as 18 months to ensure that the bacteria are killed. o Screening for tuberculosis involves the Mantoux skin test in which antigens from the bacteria are injected beneath the skin. If persons have been exposed to tuberculosis, they will develop swelling at the injection site. If persons have positive skin tests, then they may have their sputum cultured and/or receive a chest xray to determine if there is an active infection. o Tuberculosis is uncommon in much of the U.S., but its incidence has increased since the 1980s and 1990s. This increase is thought to be because of the evolution of antibiotic-resistant bacteria and the increase in people infected with HIV, homeless people, and immigrants. PULMONARY TUBERCULOSIS • • • • • A chronic infectious disease characterized by necrosis of vital lung tissue Common in the respiratory system, but can affect other body systems as well Caused by the bacterium Mycobacterium tuberculosis and related bacteria; The bacteria are most commonly transmitted in contaminated sputum expelled in the coughs of infected persons, although tuberculosis can also be caused by contaminated milk from infected cattle. This sputum may dry and settle in dust that can contain infective bacteria for a long time. The first infective exposure with the bacteria is called a primary infection. Pathogenesis o The inhaled bacteria infect the lungs and induce a chronic inflammatory response that leads to necrosis. o The tissue in this site becomes soft and cheese-like, which is why it is described as a caseous lesion. The tissue heals with fibrosis and calcification, walling off the bacteria for months or many years. These lesions are called tubercles. BRONCHOGENIC CARCINOMA • • • • • The most common type of lung cancer Danger of airway obstruction; death results from complications of obstruction or from the effects of metastatic tumors. Lung cancer is the leading cause of cancer death among both men and women. Death from lung cancer includes about 28% of all cancer deaths. Approximately 80% of lung cancer is related to cigarette smoking; lung cancer is ten times more common in smokers versus nonsmokers. Other causes include inhalation of carcinogens (cancercausing agents) which may be an occupational hazard among workers who are constantly exposed to air pollution, exhaust gases, and industrial fumes. The great danger in bronchogenic carcinoma is blockage of the airway by the malignant tumor as it grows into the PATHOPHY • 5 • • lumen of the bronchus. The affected part of the lung collapses for lack of air. Carcinoma of the lung (large white area). Symptoms and Treatment of Bronchogenic Carcinoma o The symptoms or signs of early stage lung cancer may be undetected, but later there is a persistent cough and hemoptysis. The blood in the sputum results from the erosion of blood vessels by the growing malignancy. o Anorexia, weight loss, and weakness accompany the disease. The poor oxygenation of the blood explains the generalized weakness. Symptoms include difficulty in breathing caused by the obstructed airway. o Symptoms develop late in the disease so prevention and early detection are essential. o Diagnosis of lung cancer is made from a biopsy of the tumor, detecting cancer cells in the sputum, or washings from the bronchoscopy examination. o Treatment may be surgery, radiation, or chemotherapy, depending on the particular tumor. In addition to primary carcinoma of the lungs, the lungs are a frequent site of metastases from the breast, GI tract, female reproductive system, and kidneys. Average age for diagnosing lung cancer is age 60. o AGE RELATED RESPIRATORY DISORDERS • • • CYSTIC FIBROSIS • • • • • A disease that affects all the exocrine glands of the body, the glands of external secretion Exocrine glands secrete mucus, perspiration, and digestive enzymes. The abnormality in cystic fibrosis is excessively viscous mucus secretion. Cystic fibrosis is a hereditary disease affecting young children. It is transmitted through a recessive gene carried by each parent. Before the disease was understood, the mortality rate of afflicted children was extremely high. The most serious manifestation of cystic fibrosis is in the respiratory system. The trachea and bronchi secrete thick mucus and, as it accumulates, the air passageway is blocked. Symptoms o Wheezing, persistent cough, and thick sputum; the child experiences difficulty in breathing because of the blocked airways. o The child is particularly susceptible to respiratory infections due to the abnormal mucosal lining of the respiratory tract. o Normally, bacteria are carried away by mucosal secretions, but in cystic fibrosis, the bacteria adhere to the sticky mucus. o Stationary secretions serve as a breeding ground for bacteria. Bronchiectasis (weakened and dilated bronchial tubing) is a common complication of cystic fibrosis. o Lung collapse can result from the inability to inflate them, and most deaths occur as a result of respiratory failure. Not only are mucus-secreting glands affected, the sweat glands are affected as well. The child perspires excessively and loses large amounts of salt. Susceptibility to heat exhaustion is a result. This abnormal excretion of salt is the basis for the test that confirms cystic fibrosis. Infants and youngsters may be spared some respiratory diseases like diphtheria and pertussis (whooping cough) by vaccine (DPT) injections. When young children develop asthma they may tend to outgrow it, but others who acquire asthma later tend to suffer its effects many years. For the elderly, deterioration of soft elastic tissue, which depresses the lungs’ ability to inflate and deflate properly, is a concern. o Muscles, like intercostals found in the rib cage, are less able to respond and arthritic joints interfere with a smooth breathing action. o There is usually some degree of emphysema in individuals 50–70 years of age. On average one square foot of the respiratory membrane is lost each year after age 30. DIAGNOSTIC PROCEDURES • • • • • Bronchoscopy, chest x-rays, and, when warranted, fluoroscopy, which permits visualization of the lungs and diaphragm during respiration Computerized tomography, also called a CT scan, augments chest x-rays: a series of exposed films visualize lung tissue at different depths Arterial blood gas analysis evaluates gas exchange, oxygen for carbon dioxide, blood pH, thus indicating respiratory function. Sputum examination is helpful in the evaluation of pneumonias and suspected malignancies. Gram-stained smears and cultures are useful in identifying causative organisms, determining proper antibiotic treatment, and diagnosing tuberculosis and fungal lung infections. Spirometry measures changes in gas volume in the lungs, determining ventilation capacity and flow rate. PATHOPHY • 6