Respiratory system: Asthma

Asthma: Characterized by periodic episodes of severe but reversible bronchiole obstruction due to hyperresponsive airways.

 

Problem: occurs in upper airway - obstruction to the airflow of decrease alveolar ventilation.

1)     Bronchoconstriction

2)     Inflammation of bronchiole mucosa - Edema

3)     Excess mucous production-clogs airway

 

Two Types:

1.    Extrinsic Asthma (inflammatory)

Could by hypersensitivity to an inhaled allergen/antigen

Type 1 hypersensitivity reaction: response to specific allergies

More common in children: may or may not grow out of it

 

1)     1st exposure - Allergen ® production of antibody which binds to mast cells in respiratory mucosa (bronchi & bronchioles)

2)     2nd exposure – allergen binds to the antibody, triggers the release of chemical mediators (histamine & leukotrienes)

• Bronchoconstriction - lumen size of bronchi & bronchioles
• Inflammation - Edema
• Mucous production

Narrowed, obstructed airway: difficulty getting air in & out of lungs

Lungs are fine: expiration is more difficult than inspiration, due to narrowed airway.

Forced inspiration & expiration: Hyper inflated chest - Exhausted: use more muscle to breathe

 

Allergens:

household dust, dust mites, per dander (hair), pollens (trees, flowers, grass)

 

can be avoided by avoiding allergies:

No pets, stay indoors when pollen season, use air filters, No carpets: location for microorganism (fungi) colonization – increase species

 

Treatment

• Bronchodilator: counteracts effects of chemical mediator of inflammation that cause bronchoconstriction ® relax smooth muscle (bronchodilation)
• Corticosteroid: Reduce inflammation

 

2.    Intrinsic Asthma (bronchospasms)

Hyperresponsiveness to irritants by smooth muscle in bronchi & bronchiole - Not an allergy reaction

No inflammation

No release of histamine/leukotrienes

Rather as an excessive response by muscles that are irritated.

Irritants include: Cold air, Stress

 

Exposure to chemicals that are irritating

• Cigarette smoke: when breathed in, shuts down airways, it's not an allergic reaction
• Perfume

Treatment

• Bronchodilator: relaxes smooth muscles b/c no inflammation – no corticosteroid (unless it persists & causes inflammation)

Asthma causes a sense of alarm in an individual b/c it's very difficult to breathe. Also, since expiration is much harder than inspiration, they end up with a hyperinflated chest ® ↑ sense of panic due to resistance of airflow in making you feel like you can not breathe.

 

Asthma manifestation & complications

During an asthmatic attack, the airways become narrowed d/t bronchodilation, edema, mucous plugs

 

Obstruction can be partial or complete:

Partial Obstruction

Obstruction interferes with expiration ® air trapping (air is partially expired) past the obstruction

Causes hyperinflation of the lungs

Residual volume ↑, inspiratory reserve capacity ¯ ® more energy required for breathing and involves accessory muscle to maintain ventilation & gas exchange

Complete or prolonged Obstruction

Results from mucous plugs that completely block airflow

• Atelectasis
• Ventilation & perfusion mismatch
• Hypoxemia and hyperinflation ® pulmonary hypertension
• Hypoxia & cyanosis

 

Asthma compromises air exchange: physical activity (difficult during an attack)

 

Physical S/S

• Mild attack: chest tightness, ↑ respiratory rate, prolonged expiration, mild wheezing, cough
• Severe attack: use of accessory muscles, distant breath sounds, long wheezing: fatigue, severe dyspnea, and labored speaking.
• Prolonged attack: respiratory failure: inaudible breath sounds, diminished wheezing, ineffective cough, cyanosis, and respiratory acidosis

Status Asthmaticus is severe, prolonged asthma that is unresponsive to treatment

may become fatal d/t severe hypoxia & acidosis ® cardiac arrhythmias and CNS depression

Impaired perception of dyspnea may prevent the patient from seeking medical attention

 

But both intrinsic & extrinsic asthma is referred to as acute asthma.

Repeated attacks of acute asthma cause irreversible damage – chronic asthma