Asthma Overview and Epidemiology

Study Notes

Asthma is a heterogeneous disease characterized by chronic airway inflammation.
Defined by respiratory symptoms: wheeze, shortness of breath, chest tightness, and cough that vary in intensity and over time.
Associated with variable expiratory airflow limitation.

Asthma has a global prevalence with variations by country and geographic region.
Approximately 5.4% of Nigerians are asthmatic; about 10-12% in adults and 15% in children.
In 2019, WHO estimated 262 million people worldwide had asthma, leading to 455,000 deaths.
Increasing prevalence in developing countries linked to urbanization; common onset age is around 3 years.
Male-to-female ratio of asthma in children is 2:1, equalizing at puberty.

Extrinsic Asthma: Triggered by specific external factors; often in atopic individuals with positive skin reactions to allergens.
Intrinsic Asthma: No identifiable external cause; typically begins in middle age.

Result from interaction between genetic and environmental factors.
Host Factors:
- Genetic predisposition
- Atopy (allergic conditions)
- Airway hyperresponsiveness
- Obesity
Environmental Factors:
- Indoor allergens (dust mites, pet dander)
- Outdoor allergens (pollen)
- Occupational sensitizers (isocyanates, wood dust)
- Passive smoking
- Diet and paracetamol use.

Inhalation of allergens in sensitized patients causes bronchoconstriction via IgE-dependent mechanisms.
Release of mediators like histamine and leukotrienes leads to airway constriction.
Inflammatory cells including eosinophils and macrophages play vital roles in chronic inflammation.
Increased microvascular leakage results in airway edema, mucous plugging, and inflammation.
Ongoing inflammation causes airway wall thickening due to edema, cellular infiltration, smooth muscle mass increase, and gland hypertrophy.
Chronic disease can lead to airway remodeling, resulting in fibrosis, fixed narrowing, and reduced bronchodilator response.

Characterized by recurrent exacerbations; patients are usually asymptomatic between episodes.
Symptoms worsen at night and include breathlessness, cough, wheeze, and chest tightness.
Signs include agitation, tachypnea, and tachycardia.
Acute flare-ups exhibit progressively worsening symptoms and decreased lung function.
Assessment includes FEV1, PEFR, PaO2, PaCO2, and arterial oxygen saturation.

Flare-ups classified as mild, moderate, severe, life-threatening, or near-fatal, based on symptoms and functional lung assessment.

Symptoms: Breathlessness while walking, possible agitation, end expiratory wheeze.
PEFR: ≥ 70%; relief using SABA (+/- steroid).

Symptoms: Breathless at rest, usually agitated, tachypnoea.
Pulse rate: 100-109 bpm; PEFR: 50-69% of best/predicted; relief from repeated steroid doses.

Symptoms: Breathless at rest, unable to complete sentences, loud wheezing, use of accessory muscles.
Pulse rate: ≥ 110 bpm; PEFR is critically low; potential presence of pulsus paradoxus.