Obstructive Airway Diseases (Asthma) Flashcards
Complications of Chronic Obstructive Pulmonary Diseases
- Permanent remodeling of the airway
- Chronic, persistent airflow limitation
Pulmonary Remodeling
- Increased collagen in the basement membrane causing thickening of the airway wall
- Increased smooth muscle mass
- Inflammatory cell infiltration
- Mucous gland hyperplasia
- Results in an airway that is chronically narrowed & thus, more susceptible to enhanced narrowing during smooth muscle constriction
- Clinically this causes decreased forced expiratory volume in 1 second (FEV1) & persistent airflow limitation
Atopy
Genetic predisposition to hypersensitivity reaction due to production of specific IgE antibody
- Asthmatics often suffer from allergic rhinitis or atopic dermatitis
- *Not all atopic pt’s develop asthma (combination of genetic and environmental factors)
MC allergens leading to sensitization: (1) house dust mites (2) pet fur (3) cockroaches (4) grass (5) pollen (6) rodents
Intrinsic (non-atopic) Asthmatics
Negative skin tests to inhalant allergens, normal serum IgE, usually later onset of the disease, commonly have nasal polyps, & may be sensitive to ASA
- Usually more severe, persistent asthma
- Unknown pathophysiology, but related to the increase in local IgE in airways
Infection & Asthma
- Viral infections may trigger exacerbations (unknown etiology)
- Some associations between RSV virus, mycoplasma and chlamydophila pneumonia bacteria and the development of asthma
- Specific pathophysiology is unknown
Diet & Asthma
Controversial role
- Diets low in antioxidants and vitamin D may trigger asthma
- Obesity is a risk for asthma, especially in women
Environmental Exposures & Asthma
- “Hygiene hypothesis”
- Air pollution: sulfur dioxide, ozone, diesel particulates, cigarette smoking (esp. during pregnancy)
- Occupation exposures: chemicals, fungus, animals (~10% of young adults)
Asthma Triggers
- Allergens –> activate mast cells with bound IgE, causing bronchoconstriction (MC = dust mites)
- Viral infections –> URI causes airway inflammation, eosinophils, neutorphils
- Drugs –> B-blockers (increased cholinergic bronchoconstriction) & ASA
- Exercise –> hyperventilation triggers mast cell release & bronchoconstriction (usu. lasts 30 min, worse in cold/dry climates)–B-agonists/steroids usually used as prevention
- Food –> salicylate
- Air pollution
- Occupational factors
- Hormonal factors –> premenstrual period
- GERD
- Stress
Pulmonary Function Tests
- Measure: airflow rates, lung volumes, ability of the lung to transfer gas across the alveolar-capillary membrane
- Help asses type and extent of lung dysfunction, causes of dyspnea and cough, detection of early lung dysfunction, & follow-up in response to therapy
Disadvantages: Effort-dependent, measured against predicted values derived from large studies of healthy patients, vary with age, gender, height, weight, and ethnicity
Spirometry
Measurement of how much air can be inhaled/exhaled
- Allows assessment of the presence and severity of obstructive and restrictive pulmonary dysfunction
Obstructive Dysfunction
A reduction in airflow rates (FEV1/FVC ration)
- FEV1 = forced expiratory volume in the first second
- FVC = forced vital capacity–the largest amount of air that can be forcefully exhaled after a deep breath
Restrictive Dysfunction
Marked by a reduction in lung volumes with a normal to increased FEV1/FVC ration
- Severity graded by a reduction in total lung capacity
- EX. Pulmonary fibrosis
Peak Expiratory Flow Meters
Handheld devices used by patients to monitor severity of their asthma exacerbation
- Helps set parameters for treatment measures
- Predicted values vary with age, height, and gender
- PEFs vary throughout the day–usually lowest on first awakening & highest several hours before the midpoint of the waking day
- PEF should be measured in the AM before bronchodilator administration & in the afternoon after administration
- 20% + change from AM to PM = poorly controlled asthma
Mild Intermittent Asthma
- Sxs of cough, wheeze, chest tightness, or difficulty breathing less than 2x/week
- Flare-ups brief with varying intensity
- Nighttime sxs 2+ times/month
- No sxs between flare-ups
- Lung function test FEV1 equal to or above 80% of normal values
- Peak flow less than 20% variability AM-to-AM or AM-to-PM, day to day
Mild Persistent Asthma
- Sxs of cough, wheeze, chest tightness or difficulty breathing 3-6x/week
- Flare-ups may affect activity level
- Nighttime sxs 3-4x/month
- Lung function test FEV1 equal to or above 80% of normal values
- Peak flow less than 20-30% variability
Moderate Persistent Asthma
- Sxs of cough, wheeze, chest tightness or difficulty breathing daily
- Flare-ups may affect activity level
- Nighttime sxs 5+ times/month
- Lung function test FEV1 between 60-80% of normal values
- Peak flow greater than 30% variability
Severe Persistent Asthma
- Sxs of cough, wheeze, chest tightness, or difficulty breathing continually
- Nighttime sxs frequently
- Lung function test FEV1 less than or equal to 60% of normal values
- Peak flow greater than 30% variability
Goals of Asthma Therapy
- Reduce/eliminate chronic sxs
- Eliminate exacerbations/ED visits
- Reduce need for B-agonists
- Reduce side effects of medications
- Eliminate activity restrictions
- Children follow a step-wise approach to therapy starting with B2-agonists then adding additional agents as needed
Airway Hyper-Responsiveness
- Exaggerated bronchoconstrictor response to stimuli
- Related to inflammation and structural changes
- Reduced when inflammatory inflammation is treated
Airway Obstruction
Symptoms: Chest tightness, cough, wheezing
Causes:
- Airway smooth muscle constriction
- Airway edema
- Mucus hyper-secretion
- Airway remodeling
Disposition
Discharge vs. Admission, consider
- Social situation (i.e., homelessness, access to medications)
- Prior hospitalizations
- Compliance history
- History of intubation
Discharge:
- Resolution of symptoms (improved PEF or FEV to > 70% predicted value)
- Pulse oximetry of at least 92%
- Pt can speak, eat, and drink with ease
Admit:
- Poor/slow response to treatment (PEF or FEV < 40% predicted value)
B1-Receptors
- Adrenergic*
- Widely expressed in the airways
- Relax smooth muscle
- Inhibit inflammatory cells
- -> B2-agonists facilitate this (prevent smooth muscle contraction) (e.g. Albuterol, Salmeterol)
- Usually given via inhalation
Leukotrienes
- Inflammatory mediators produced by mast cells that cause bronchoconstriction
- -> Antileukotrienes block receptors
- Less effective than ICS (used in conjunction in pts not controlled w/ ICS)
Asthma & Poverty
Asthma in poor pts causes more…
- Frequent asthma symptoms (every day or every week)
- School absenteeism
- Poor health status
- ED visits (2x higher)
Causes:
- Lack of health insurance, regular primary care, and/or asthma management plans
- Increased exposure to second-hand smoke, cockroaches, air pollution, and allergens
Pathology of Cigarette Smoke
Affects large airways, small airways (< or equal to 2mm diameter), & alveoli
Large airways:
Goblet cell increase in #, bronchi undergo squamous metaplasia, smooth muscle hypertrophy & bronchial hyperactivity, neutrophil influx, neutrophil elastase (proteolytic)
