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C H A P T E R 18 Asthma Carlin Chapter 18 Disease Definition • Asthma is a chronic inflammatory disorder of the airways with airway hyperresponsiveness that leads to recurrent episodes of wheezing, breathlessness, chest tightness, and coughing occurring particularly at night or in the early morning. • These episodes are usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment. Scope • A worldwide problem with an estimated 300 million affected • 22 million Americans affected • 5% increase per year in the world • Most childhood asthma begins in infancy (<3 yr of age) • Higher in some populations (23% of innercity African Americans vs. 5% of Caucasians) Pathophysiology • Inflammation is the primary issue that leads to airflow limitations, which includes bronchoconstriction, airway hyperresponsiveness, and airway edema. • Asthma involves the interplay between a number of host (innate immunity, genetics) and environmental factors (airborne allergens, viral respiratory infections). (continued) Pathophysiology (continued) • Inflammation most pronounced in the medium-sized bronchi • CD4 lymphocyte believed to promote inflammation by the eosinophils and mast cells • Structural changes (subepithelial fibrosis via deposition of collagen fibers) (continued) Pathophysiology (continued) • Hypertrophy and hyperplasia of the airway smooth muscle • Angiogenesis (proliferation of new blood vessels) • Increased mucus hypersecretion • Airway hyperresponsiveness ultimately leading to airway narrowing (continued) Pathophysiology (continued) • See figure 18.1 for illustrations of normal tissue, swelling, and remodeling. Signs and Symptoms • Symptoms: episodic wheezing, breathlessness, cough, and chest tightness • Can be intermittent, making it difficult to diagnose • Can be related to exposure to allergens, seasonal rhinitis, dust mites, smoke, strong fumes, cold air, and exercise (exerciseinduced bronchospasm, EIB) • Death can be associated with mild asthma History and Physical Examination • Medical history should address: – Presence of symptoms – Pattern of symptoms – Physical examination of the chest • Diagnostic testing (spirometry): – FEV1 (<80% of predicted) – FEV1/FVC (<65% of predicted) – Flow–volume loop (continued) History and Physical Examination (continued) • Asthma will show improvements in spirometry following bronchodilator administration. • See figure 18.2 for flow–volume tracings of a patient with asthma and a patient with emphysema. (continued) History and Physical Examination (continued) • Bronchial provocation testing – Methacholine or histamine – >20% decline in FEV1 following administration of the irritant suggestive of asthma – Exercise challenge may be useful to uncover airflow limitations (continued) History and Physical Examination (continued) • Other studies – Chest roentgenogram – Sputum production (eosinophilic or neutrophilic inflammation) – Consider other causes for patient’s symptoms (pneumonia, pneumothorax, congestive heart failure) Exercise Testing • Generally reserved for those with an unusual decline in exercise tolerance not related to the degree of airflow limitations • Symptom-limited incremental test • Measurements helpful for assessing asthma include: – Oxyhemoglobin saturation – Heart rhythm (ECG) . . – Metabolic cart (VO2, VCO2, anaerobic threshold) (continued) Exercise Testing (continued) • Contraindications – Acute bronchospasm – Chest pain – Increased level of shortness of breath above normal – Severe exercise deconditioning – Other comorbid conditions such as unstable angina; orthopedic limitations (continued) Exercise Testing (continued) • Exercise-induced bronchospasm (EIB) – EIB occurs in 50% to 100% of patients with asthma – Typical response: initial bronchodilation during first 10 min followed by a progressive bronchospasm, peaking 10 min following completion of exercise, and resolution of EIB over the next 60 min. – Protocol: 2 min stages, 1 MET increments, maximum effort 8 to 12 min. Spirometry testing immediately following exercise and repeated at 15 and 30 min to assess airflow limitation. Treatment • Goal—control the overall disease process to reduce impairment and reduce ongoing risks associated with disease • Classification of severity useful for initial treatment but not ongoing treatment • Focus on asthma control, defined as the degree to which the manifestations of the disease are minimized by therapeutic interventions and the goals of therapy are met and should be assessed and monitored to adjust therapy • See table 18.2 on components of asthma severity by clinical features before treatment. Medications • Long-term control (used daily to achieve and maintain control of persistent asthma) – Corticosteroids – Cromolyn and nedocromil immunomodulators – Leukotriene modifiers – Long-lasting beta-agonists – Methylxanthines (continued) Medications (continued) • Quick-relief medications – Anticholinergics – Short-acting beta-agonists – Systemic corticosteroids Prevention (EIB) • Appropriate warm-up (15 min at 60% of . VO2max) • 15 min of moderate-intensity exercise should precede significant exercise for active persons with asthma (continued) Prevention (EIB) (continued) • A mask or scarf over the mouth and nose may be helpful to reduce cold-induced EIB. • People that don’t respond to the nonpharmacologic approach can use pharmacologic intervention prior to exercise. Exercise Prescription 1. Assess patient’s underlying respiratory status and goals for exercise. 2. Assess maximum level of exercise. 3. If maximum level of exercise has been determined by measurement of oxygen consumption and carbon dioxide production (cardiopulmonary exercise testing), begin exercise prescription at an initial intensity level just below the anaerobic threshold. (continued) Exercise Prescription (continued) 4. If such measurements are unavailable, begin exercise at a level of exercise at which the patient is comfortable performing for 5 min. 5. Instruct the patient to continue exercise for 20 to 60 min per session. 6. Have the patient perform sessions 3 to 5 times per week. (continued) Exercise Prescription (continued) 7. Increase exercise intensity by 5% with each session. 8. When maximal level of intensity is attained, increase exercise duration by 5%. Exercise Prescription (Special Considerations) • Exposure to cold air, low humidity, or air pollutants should be minimized. • Intermittent exercise or lower-intensity sports performed in the presence of warm, humid air are generally better tolerated. (continued) Exercise Prescription (Special Considerations) (continued) • If maximal oxygen consumption is obtained using a metabolic cart, training can be initiated at an intensity level of 50% to 85% of the heart rate reserve. • For patients with more limiting asthma, a target intensity based on perceived dyspnea (such as a Borg scale) may be more appropriate. Conclusion • Asthma represents airway narrowing secondary to airway inflammation and bronchoconstriction. Environmental risk factors or other triggers (such as exercise, cold air) can initiate an allergic response, leading to airway hyperresponsiveness. (continued) Conclusion (continued) • Exercise limitations and decreased levels of fitness frequently are noted in patients with asthma but in many instances are not considered to be important for some time following the initial development of symptoms. Exercise limitations and fitness levels can be improved in those patients treated with an appropriate medication and exercise regimen.