How can I write an introduction for a literature review on Chronic Obstructive Pulmonary Disease (COPD), global climate change, air pollution, and acute exacerbations?

Writing an Introduction for a Literature Review on COPD, Climate Change, Air Pollution, and Acute Exacerbations

Establishing the Disease Burden and Definition

Begin your introduction by establishing COPD as a major global health crisis, defining it as a common, preventable, and treatable disease characterized by persistent respiratory symptoms and airflow limitation due to airway and/or alveolar abnormalities, usually caused by significant exposure to noxious particles or gases 1. COPD ranks as the third leading cause of death worldwide and the second leading cause of disability-adjusted life-years lost 1. This disease burden is particularly relevant given that COPD-related mortality more than doubled among women over a 20-year observation period 1.

Linking Environmental Exposures to COPD Pathogenesis

Your introduction should establish that while tobacco smoking remains the most well-studied COPD risk factor, environmental exposures including biomass fuel exposure and air pollution are increasingly recognized as significant contributors to disease development and progression 1. This sets the foundation for your climate change discussion by emphasizing that environmental exposures like air pollution may contribute to COPD beyond traditional smoking-related pathways 1.

• Indoor pollution from biomass cooking and heating in poorly ventilated dwellings represents a documented risk for COPD development 1
• Occupational exposures to organic and inorganic dusts, chemical agents, and fumes are underappreciated risk factors for COPD 1

Defining and Contextualizing Acute Exacerbations

Frame acute exacerbations as critical events that represent acute worsening of respiratory symptoms requiring additional therapy, which negatively impact health status, rates of hospitalization and readmission, and disease progression 1. Exacerbations now account for 50% to 75% of the costs associated with COPD 1.

Key characteristics to emphasize:

• Exacerbations are mainly triggered by respiratory viral infections, though bacterial infections and environmental factors may also initiate and/or amplify these events 1
• Patients susceptible to frequent exacerbations (defined as two or more per year) have worse health status and morbidity than those with less-frequent exacerbations 1
• At 8 weeks post-exacerbation, 20% of patients have not recovered to their pre-exacerbation state 1

Connecting Climate Change to Air Pollution and COPD Outcomes

This is where your literature review's unique contribution emerges: establish that ongoing climate change is expected to increase air pollution levels, global temperature, and the frequency and severity of extreme weather events, all of which are associated with COPD exacerbations 2. Recent evidence demonstrates that exposure to various environmental factors increases the risk of exacerbations 2.

Present the mechanistic pathway:

• Long- and short-term exposures to higher levels of particulate-rich air pollution are associated with increased COPD exacerbation, hospitalization, and mortality 3
• Short-term exposures to sulfur dioxide (SO₂) show strong associations with COPD exacerbation risk (odds ratio = 2.45 per 1 ppb increase), even in areas with air pollution levels below EPA standards 4
• Temperature, humidity, ozone (O₃), carbon monoxide (CO), particulate matter up to 10 μm (PM₁₀), and nitrogen dioxide (NO₂) all show significant associations with hospital admissions for COPD exacerbations 5

Highlighting the Climate-Pollution-COPD Nexus

Emphasize that climate-mediated air pollution represents a particularly insidious pathway, where climate variables influence air pollution levels, which in turn affect COPD severity 6. This creates a complex interplay:

• PM₂.₅ fully mediates associations between temperature and oxygen saturation, as well as emphysema severity 6
• NO₂ fully mediates the association between relative humidity and forced expiratory volume in 1 second (FEV₁) 6
• Hospital admissions and mortality from COPD exacerbations are more frequent in autumn and winter, with lower temperatures at admission associated with higher probability of in-hospital mortality 5

Framing the Knowledge Gap and Research Imperative

Conclude your introduction by noting that despite these established associations, patient-focused methodological approaches are needed to better understand and quantify these relationships, so that effective mitigation strategies that decrease the risk of exacerbations can be developed 2. The American Thoracic Society and European Respiratory Society have identified significant knowledge gaps in understanding environmental triggers for COPD exacerbations 1.

Critical gaps to highlight:

• The need for studies using clinically defined exacerbations rather than simply counting emergency department visits and hospital admissions, as these may be more sensitive to environmental triggers 4
• The requirement for better understanding of which COPD endotypes are most susceptible to climate-mediated air pollution effects 3
• The necessity of identifying patient-centered outcomes that matter most to COPD patients in the context of environmental exposures 1

This framework positions your literature review as addressing a timely and clinically significant intersection of respiratory disease, environmental health, and climate science, with direct implications for patient morbidity, mortality, and quality of life.