Advanced Asthma Training Course Mechanisms Of Asthma Part II Dr.Hadeel A.K AlOtair ABIM,MRCP(UK),FCCP Assisstant professor of Medicine consultant pulmonologist

Advanced Asthma Training Advanced Asthma Training CourseCourse

Mechanisms Of Asthma Part II

Dr.Hadeel A.K AlOtair ABIM,MRCP(UK),FCCPAssisstant professor of Medicine consultant pulmonologist

King Khalid University Hospital


Airway Hyperresponsiveness

• It is the characteristic functional abnormality of asthma.

• It results in (exaggerated) airway narrowing in response to a stimulus.

• This leads to variable airflow limitation and intermittent symptoms.

• It is partially reversible with therapy.


Source: Peter J. Barnes, Source: Peter J. Barnes, MDMD

Mechanisms:

AHR is linked to Inflammation


Mechanism of airway Hyper responsiveness

• Gene(s) responsible for AHR is located near a major locus that regulates serum IgE levels on chromosome 5q.

• Useful in the diagnosis of asthma



Uncouplingof airway contractionUncouplingof airway contraction May lead to May lead to excessive narrowing of the airways with loss of the excessive narrowing of the airways with loss of the maximum plateau of contractionfound in normal maximum plateau of contractionfound in normal airwaysairways

Thickening of the airway wallThickening of the airway wall by edema and by edema and structural changes amplifies airway narrowingstructural changes amplifies airway narrowing




Sensory nerves maySensory nerves may be sensitised by inflammation,leading be sensitised by inflammation,leading to exaggerated bronchoconstrictionto exaggerated bronchoconstriction

Excessive contraction of airwayExcessive contraction of airway smooth musclesmooth muscle may may result from increased Volume and/or airway smooth result from increased Volume and/or airway smooth muscle cellsmuscle cells




Acute exacerbations

• Transient worsening of Asthma may occur as a result of exposure to certain triggers. e,g Exercise,air,pollutants or certain weather conditions .

• Prolonged worsening is usually due to viral infection of the upprt respiratory tract (Rhino virus, respiratory syncytial virus) or allergen exposure.


Virus Induced Asthma Exacerbation:Possible Mechanisms

2- Mediator production2- Mediator production :: Kinnin ,complement , Kinnin ,complement , arachiodonic acid metabolitearachiodonic acid metabolite

1-Epithelial 1-Epithelial disruptiondisruption : :Reduced ciliary clearance, Reduced ciliary clearance, permeability, loss of protective functionpermeability, loss of protective function

3-Induction of inflammation3-Induction of inflammation ::cytokines , cytokines , chomokineschomokines

4-Alteration of neural Responses4-Alteration of neural Responses :: increased increased cholinergic activitycholinergic activity

5-IgE- dysregulation5-IgE- dysregulation :: increased total IgEincreased total IgE



Nocturnal Asthma

• Nocturnal Worsening of asthma

• May be related to the circadian rhythm of circulating

• hormones :epinephrine,cortisol,melatonin

• Neural mechanism: Cholinergic tone

• Increase in airway inflammation





Irreversible airflow limitation

• Progressive airflow limitation that is not fully reversible.

• It develops in some patients with severe asthma

• It may reflect changes in airway structure in chronic asthma

• Can result in accelerated fall in lung function






Difficult- to- treat asthma

• Confirm the diagnosis: Viral bronchiolitis Vocal cord dysfunction COPD• Poor compliance to treatment

• Complicating conditions (Chronic sinusitis, GERD. smoking, OSA/obesity)

• Psychological and psychiatric disorders

• Genetic factors: poor response to glucocorticoid


Difficult- to- treat asthma

• Many are difficult to treat from the onset of the disease

• Airway closure leads to air trapping and hyperinflation

• Pathology: increase in neutrophils more small airway involvement more structural changes.


Smoking and Asthma

•The cigarette burns out but the

inflammation rages on . S-Shapiro


Smoking and Asthma

• Asthma is more difficult to control

• more frequent exacerbations

• more hospital admissions • more rapid decline in lung function

• Fixed airway obstruction • increase risk of death


Smoking and Asthma

• They may have neutrophil predominant inflammation in their airway

• poorly responsive to inhaled & oral glucocorticoids.


YYYYYY

Mast cellMast cell

CD4+ cellCD4+ cell(Th2)(Th2)

EosinophilEosinophil

AllergensAllergens

Ep cellsEp cells

ASTHMAASTHMA

BronchoconstrictionBronchoconstrictionAHRAHR

Alv macrophageAlv macrophage Ep cellsEp cells

CD8+ cellCD8+ cell(Tc1)(Tc1)

NeutrophilNeutrophil

Cigarette smokeCigarette smoke

Small airway narrowingSmall airway narrowingAlveolar destructionAlveolar destruction

COPDCOPD

Reversible Irreversible

Airflow LimitationAirflow Limitation

Source: Peter J. Barnes, MD



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Advanced Asthma Training Course Mechanisms Of Asthma Part II Dr.Hadeel A.K AlOtair ABIM,MRCP(UK),FCCP Assisstant professor of Medicine consultant pulmonologist