Indoor Heat, Air Quality Increase Symptoms in COPD

As indoor air temperatures increase, so do symptoms of chronic obstructive pulmonary disease (COPD), according to a new study published in the Annals of the American Thoracic Society. In homes where levels of air pollutants are high, the impact on symptoms is even greater.

“Previous studies have found that the elderly are particularly vulnerable to the effect of heat and more likely to die or be hospitalized during heat waves,” said Meredith C. McCormack, MD, MHS, an associate professor of medicine at Johns Hopkins University and lead study author. Dr McCormack explained that the Hopkins study was designed to build on existing findings by looking at exposure at the individual level and included in-home assessment of temperature and specific health effects of COPD. “To our knowledge,” she was quoted in a press release, “this is the first study to report an interactive effect between indoor temperature and indoor air pollution in COPD.”

Sixty-nine participants with moderate-to-severe COPD were enrolled in a longitudinal cohort study conducted in Baltimore, MD, during the hottest days of the year.  

Participants assessed lung function daily using spirometry and recorded use of rescue inhalers to manage symptoms. They also completed a daily questionnaire that included the Breathlessness, Cough, and Sputum Scale (BCSS), which provides a standardized rating of respiratory symptoms.

This information was analyzed along with measurements of two in-home air pollutants-fine particulate matter (PM2.5) and nitrogen dioxide (NO2)-as well as outdoor temperatures during the study period.

Researchers found:

• Participants spent the majority of their time indoors. On the days they did go out, they spent on average about two hours.
• BCSS scores worsened and use of rescue inhalers increased with rising indoor temperatures.
• The effect of higher indoor temperatures was magnified by high levels of PM2.5 and NO2. A 10 degree increase in temperature in a home at the 75th percentile of PM2.5 levels resulted in a severe increase in symptoms, compared to only a mild increase in symptoms that occurred when the home was at the 25th percentile of PM2.5.
• The effects of higher indoor temperatures were experienced immediately and continued for one to two days.
• Spirometric lung function was unaffected by increasing temperatures or higher levels of indoor air pollutants.
• Although 86% of participants lived in a home with some form of air conditioning, it was not used during 37% of study days.

On days that participants went outside, increases in daily outdoor temperatures were associated with increased BCSS scores after adjusting for outdoor air pollution concentrations.

Research on health consequences related to outdoor PM2.5 and ozone levels in US cities reveals that reducing levels of these pollutants below those set by the EPA could significantly reduce mortality and morbidity and decrease absence from school and work.

The authors conclude that for patients with COPD who spend the majority of their time indoors, indoor heat exposure during warmer months is a modifiable environmental exposure that may contribute to poor respiratory outcomes.

As climate change contributes to rising global temperatures Dr McCormack believe the current study findings offer health care professionals an opportunity for targeted intervention and challenge policy makers to devise strategies that optimize indoor environmental conditions for those most vulnerable to heat.

Potential study limitations include being geographically confined to Baltimore and the decision to not measure indoor ozone levels because previous studies found those levels to be low indoors in the city.