Lecture 10: Asthma Flashcards
Define asthma
An inflammatory process that leads to hyperresponsive airways and reversible airway obstruction
Causes of airflow obstruction (7 parts)
Bronchoconstriction, mucus plugging, bronchial wall edema, inflammatory infiltrate, airway remodeling (fibrosis), SM hypertrophy, uncoupling elastic recoil forces
Asthma represents an intra or extrathoracic obstruction. What does this mean for flow limitation during inspiration and expiration?
Intrathoracic: flow is decreased during expiration
How do we define obstruction (FEV1 / FVC)
FEV1 / FVC ratio of less than 0.7
Can you normalize obstruction with a bronchodilator in asthma?
Yes, you can completely normalize the FEV1 / FVC ratio
What is air trapping?
As aspect of asthma in which the alveolus cannot release air, leading to expanded alveolus
What does air trapping cause (in terms of RV/VC)?
Residual volume is greater, vital capacity is lower proportionally to TLC (which is fixed)
V/Q in asthma
Hypoxemia from V/Q mismatch (some airways more affected than others)
Mild asthma attack vs severe (in terms of PCO2)
PCO2 falls as functioning units can remove CO2; severe attacks can cause a rise in PCO2
Why does asthma increase pulsus paradoxus?
Large swings in intrapleural pressure due to battling increased pulmonary resistance increases pulsus paradoxus
Describe allergic asthma
Asthma exacerbated by exposure to various allergens
Allergic asthma pathophysiology (be sure to identify two phases)
An initial allergen causes an increase in Th2 CD4 cells, which release TH2 cytokines; re-exposure leads to IgE cross-linking on mast cells and histamine dumping + leukotrience production (early phase) –> bronchoconstriction and perpetuated inflammation via major basic protein (late phase)
Hygiene hypothesis
Exposure to infections early in life –> development of Th1-mediated response (protective immunity) and down regulation of Th2-mediated immune response (allergic diseases)
Th2 Cytokines
IL-4 –> B cells to synthesize IgE; IL-5 –> eosinophil maturation; IL-9 –> mast cell recruitment; IL-13 –> airway hyperresponsivneess and mucous secretion
Exercise-induced asthma pathophysiology
Exercise can provoke bronchoconstriction via cooling of air leading to fluid accumulation
Describe aspirin-exacerbated respiratory disease
Inhibition of cyclooxygenase pathway can shift pathway to production of bronchoconstrictor leukotrienes
Airway remodeling leads to…
Persistent airflow obstruction
Describe some features of airway remodeling (5)
Increase SM mass, increased mucous glands, inflammatory cells persist (ongoing inflammation), fibrosis/collagen deposition, elastolysis
Symptoms of asthma
Cough, dyspnea, wheezing, chest tightness
Signs of asthma
Wheezing, prolonged expiratory phase
Why would you have no wheezing with severe asthma?
If asthma is so bad there is no airflow
What is status asthmaticus?
Severe asthma attack refractory to treatment w/ bronchodilators that may require assisted ventilation
What can be used during bronchoprovocation test?
Methacholine (stimulates SM receptors), mannitol (mast cell mediators), exercise, eucapnic voluntair hyperpnea
If you give methacholine or mannitol, what do you measure?
PC20: conc of provacative med needed to cause fall in FEV1 by 20% (lower conc, higher chance of asthma)
