The Impact of Extreme Heat Waves and Air Pollution on the Prognosis of Chronic Airway Diseases

Climate change has led to a global increase in temperatures, and according to NASA, 2024 was the hottest year on record since 1850. Extreme heatwaves (EHW) represent one of the most significant manifestations of this crisis. While the adverse effects of air pollution on chronic respiratory diseases are well documented, the impact of extreme heatwaves on asthma and chronic obstructive pulmonary disease (COPD) has received less attention.

This study was designed to prospectively evaluate the effects of extreme heatwaves and air pollution on patients with asthma and COPD. The study was conducted in Mersin, Türkiye, between February and December 2024. Individuals with physician-diagnosed asthma or COPD who attended the outpatient clinic were enrolled.

Baseline assessments were performed on days with normal seasonal weather. Lung function was measured using spirometry, and airway inflammation was assessed using fractional exhaled nitric oxide (FeNO). Symptom control and quality of life were measured using validated questionnaires: the Asthma Control Test (ACT) and Asthma Quality of Life Questionnaire (AQLQ) for patients with asthma, and the Modified Medical Research Council (mMRC) scale and COPD Assessment Test (CAT) for patients with COPD.

Meteorological variables, including temperature, humidity, and wind, as well as daily air pollution levels, were obtained from official sources. On documented extreme heatwave days, participants were recalled for follow-up visits. At these visits, spirometry, FeNO, and questionnaire assessments were repeated. Information regarding exacerbation episodes requiring systemic corticosteroid use or hospitalization during the study period was also collected.

The study was designed to compare patient-level outcomes between normal weather days and extreme heatwave days. The overall objective was to investigate how environmental stressors such as heat and air pollution influence disease control, quality of life, symptoms, lung function, and airway inflammation in patients with asthma and COPD.

Inclusion criteria

• Age ≥ 18 years
• Provision of written informed consent

For the asthma group:

• Diagnosis of asthma for at least 6 months according to the GINA 2024 guidelines

Variable respiratory symptoms together with documented variable expiratory airflow limitation, demonstrated by at least one of the following:

• Positive bronchodilator reversibility test (>12% and >200 mL increase in FEV1 10-15 minutes after 400 μg salbutamol)
• Peak expiratory flow (PEF) variability (>10% average daily PEF variability over 2 weeks)
• Positive delayed reversibility (improvement in lung function after 4 weeks of anti-inflammatory treatment with >12% and >200 mL increase in FEV1 or >20% increase in PEF)
• Positive bronchial provocation test (≥20% fall in FEV1 with standard doses of methacholine or histamine)
• Stable disease for at least 4 weeks prior to enrollment

For the COPD group:

• Diagnosis of COPD for at least 6 months according to the GOLD 2024 guidelines (post-bronchodilator FEV1/FVC <70% in the presence of compatible clinical findings)
• Stable disease for at least 4 weeks prior to enrollment

Exclusion criteria

• Presence of other pulmonary diseases apart from asthma or COPD (e.g., interstitial lung diseases, pleural diseases, pulmonary vascular diseases)
• Pregnant women
• History of cancer within the past 5 years
• Previous lung surgery
• Active pulmonary tuberculosis
• Respiratory tract infection within the last 4 weeks
• Presence of significant extrapulmonary disease that may affect lung function (e.g., cerebrovascular disease, acute myocardial infarction)
• Active smoking within the past year
• Residence outside the central district of Mersin