Porth's Essentials of Pathophysiology, 4e

540

Respiratory Function

U N I T 6

upper respiratory tract. 2 The influenza virus can infect both the upper and lower respiratory tracts. Bacteria can infect the nose and sinuses, and both bacteria and fungi can produce infections of the lung, many of which cause significant morbidity and mortality. The Common Cold The common cold is a viral infection of the upper respi- ratory tract. It occurs more frequently than any other respiratory tract infection. Most adults have two to three colds per year, whereas the average school child may have up to 12 per year. 3 The condition usually begins with a sore and scratchy throat followed by pro- fuse and watery rhinorrhea, nasal congestion, sneezing, and coughing. Other cold symptoms include malaise, fatigue, headache, hoarseness, sinus congestion, and myalgia. Fever is a common sign in children but is an infrequent finding in adults. 3 The disease process is self- limited, usually lasting up to 10 days. Initially thought to be caused by either a single “cold virus” or group, the common cold is now recognized to be associated with many different viruses. 3,4 The most common are the rhinoviruses, parainfluenza viruses, respiratory syncytial virus, coronaviruses, and adenovi- ruses. Of these, the rhinoviruses are the most common cause of colds in persons between 5 and 40 years of age. In children younger than 3 years of age, infections from the respiratory syncytial virus and parainfluenza viruses are most common. The “cold viruses” are rapidly spread from person to person. Children are the main source of infection often acquiring a new strain of the virus from another child in school or day care. The fingers are the greatest source of spread, and the nasal mucosa and conjunctival surface of the eyes are the most common portals for entry of the virus. The most highly contagious period is during the first 3 days after the onset of symptoms, and the incuba- tion period is approximately 5 days. Cold viruses have been found to survive for more than 5 hours on the skin and hard surfaces, such as plastic countertops. 4,5 Aerosol spread of colds through coughing and sneezing is much less important than the spread by fingers picking up the virus from contaminated surfaces and carrying it to the nasal membranes and eyes. 5 This suggests that careful attention to hand washing is one of the most important preventive measures for avoiding the common cold. Because the common cold is an acute and self-limited illness in persons who are otherwise healthy, symptom- atic treatment with rest and antipyretic drugs is usually all that is needed. Antibiotics are ineffective against viral infections and are not recommended. 6 Over-the-counter (OTC) remedies are available for treating the symptoms of a common cold. Antihistamines are popular OTC drugs because of their action indrying nasal secretions. Although they do not work as a monotherapy, a first-generation antihistamine in combination with a decongestant may be slightly beneficial in relieving general symptoms, nasal congestion, and cough. 6 However, there is no evidence that they shorten the duration of the cold. They are not recommended for use in children. Decongestant drugs

(i.e., sympathomimetic agents) are available in OTC nasal sprays, drops, and oral cold medications. These drugs constrict the blood vessels in the nasal mucosa and reduce nasal swelling. Rebound nasal swelling can occur with indiscriminate or chronic use of nasal drops and sprays. Oral preparations containing decongestants may cause systemic vasoconstriction and elevation of blood pressure when given in doses large enough to relieve nasal congestion, and they should be avoided in persons with hypertension, heart disease, hyperthyroidism, dia- betes mellitus, or other health problems. 3 Rhinosinusitis The term rhinitis refers to an inflammation of the nasal passages and sinusitis to an inflammation of the para- nasal sinuses. 7–12 Although it has not been universally accepted, the suggestion has been made that the term rhinosinusitis is a more accurate term for what is com- monly referred to as sinusitis , because the mucosa of the nasal cavities and paranasal sinuses are lined with a continuous mucous membrane layer and sinusitis rarely occurs in the absence of infectious or allergic rhinitis. The paranasal sinuses are air-filled extensions of the respiratory part of the nasal cavities into the frontal, ethmoid, sphenoid, and maxilla bones (Fig. 22-1A). The sinuses, which are named for the bones in which they are found, are connected by narrow openings or ostia with the superior, middle, and inferior nasal turbinates of the nasal cavity. The anterior ethmoid, frontal, and maxillary sinuses all drain into the nasal cavity through a relatively convoluted and narrow passage called the ostiomeatal complex (see Fig. 22-1B). The sphenoidal sinuses drain from a separate complex between the sep- tum and the superior turbinate (see Fig. 22-1C). The most common causes of rhinosinusitis are con- ditions that obstruct the narrow ostia that drain the sinuses. Most commonly, rhinosinusitis develops when a viral upper respiratory tract infection or allergic rhi- nitis obstructs the ostiomeatal complex and impairs the mucociliary clearance mechanism. Nasal polyps also can obstruct the sinus openings and facilitate sinus infec- tion. Infections associated with nasal polyps can be self-perpetuating because constant irritation from the infection can facilitate polyp growth. Barotrauma caused by changes in barometric pressure, as occurs in airline pilots and flight attendants, may lead to impaired sinus ventilation and clearance of secretions. Swimming, div- ing, and abuse of nasal decongestants are other causes of sinus irritation and impaired drainage. Maxillary sinusitis may result from dental infection, and teeth that are ten- der should be carefully examined for signs of an abscess. Clinical Features Rhinosinusitis can be classified as acute, subacute, or chronic. 7,8 Acute viral rhinosinusitis may last from 5 to 7 days and acute bacterial rhinosinusitis up to 4 weeks. Subacute rhinosinusitis lasts from 4 weeks to less than 12 weeks, whereas chronic rhinosinusitis lasts beyond 12 weeks.