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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.