Small Study Finds High Temperatures Worsen Breathing Problems in Patients With COPD

A recent study found that higher temperatures were associated with worse breathing symptoms and low temperatures were associated with symptoms of bronchitis in participants with chronic obstructive pulmonary disease (COPD).

Patients with chronic obstructive pulmonary disease (COPD) had differing breathing symptoms in different temperatures, such as dyspnea in higher temperatures and cough and phlegm symptoms in cold temperatures, according to a study published in ERJ Open Research. The study aimed to examine how daily personal and outdoor temperature exposure in the warm and cold seasons affects daily lung function, breathing, and bronchitis symptoms among community-dwelling patients with COPD.

The study took place at Harvard Medical School in Boston, Massachusetts. The study population included 30 participants with COPD who had formerly smoked and were recruited as part of the Study of Air Pollution and COPD Exacerbation at the Beth Israel Deaconess Medical Center in Boston.

Eligible participants had to have a home address within 50 km of the Harvard Supersite air pollution and temperature monitor at Harvard Medical School and had to have a clinical diagnosis of COPD with at least moderate airflow obstruction. Participants with a history of lung cancer, interstitial lung disease, or bronchiectasis were not eligible to participate in this study.

The study took place between February 24, 2017, and January 17, 2019. Height, weight, demographic information, past medical history, and baseline measure of lung function were all collected once patients entered into the study. Participants were instructed on how to use a portable spirometer and a personal air quality monitor (PAM) for use in identifying indoor and outdoor temperatures.

Participants were observed for up to 4 nonconsecutive 30-day periods, which were in 4 different seasons over the course of 12 months. All participants measured their daily lung function in the morning before any medications. At the end of the study, 30 participants had a total of 3314 observation-days.

Daily exposure to temperature and relative humidity were calculated using the portable PAMs, and outdoor exposure was calculated using the temperature and relative humidity monitor on the roof of Countway Library at Harvard Medical School. All exposure measures from the PAM devices were sent to stationary monitors in the Boston area. During periods of repeated calibration, 24-hour averages of temperature and relative humidity from a reference PAM were compared with a state-owned stationary monitor in Boston using linear regression models.

Daily personal exposure to air pollutants, including fine particle matter, was measured by the PAM devices. Outdoor exposure to pollutants was measured with the state-owned stationary monitor in Boston.

Mean previous-day 24-hour exposure to temperature from the PAM devices (personal exposure) and outdoor state-owned stationary monitors in the Boston area (outdoor exposure) were calculated. Multilevel linear mixed-effects models to assess associations between 1-, 2-, and 3-day 24-hour exposure to personal and outdoor temperature and lung function were also constructed. Seasons were categorized as winter, spring, summer, or fall based on calendar dates of each month.

All models were run using stratum-specific associations for warm (May-September) and cold (October-April) seasons. The temperature was also examined when assessing the association between exposure to temperature (personal or outdoor) and morning lung function and symptom outcomes based on previous 1-, 2-, and 3-day moving averages of temperatures. Sensitivity analyses for adjusting temperature models for previous-day particle matter were also performed in separate models.

Of the 30 participants, the mean (SD) age was 71.1 (8.4) years. The participants were predominantly White (80.0%) and there were more female participants (53.3%). The participants mostly had some level of college education or an associate degree or higher (73.3%). The 30 participants had a mean (SD) of 54.4 (30.7) pack-years of smoking. Participants were evenly distributed over income categories.

The mean (SD) personal temperature exposure was 21.5 (2.2) °C for all seasons, 20.8 (2.1) °C for the cold season, and 22.3 (2.0) °C for the warm season. The mean (SD) outdoor temperature was 12.0 (9.6) °C for all seasons, 5.6 (7.1) °C for the cold season, and 20.3 (5.2) °C for the warm season. There was no association between 1-, 2-, and 3-day moving average personal and outdoor temperature exposure and morning lung function in all seasons or in the cold or warm seasons.

Higher temperature exposure as measured by the PAM was associated with greater odds of worsened breathing symptoms. In adjusted mixed-effects models, each 5 °C higher previous-day personal exposure to temperature was associated with 1.85 (95% CI, 0.99-3.48) higher odds of worsening breathing symptoms. The 2-day (odds ratio [OR], 2.23; 95% CI, 1.05-9.72) and 3-day (OR, 2.26; 95% CI, 0.91-5.58) results were similar.

There were also positive associations between each 5 °C higher 1-day moving average personal temperature exposure and odds of worsening breathing symptoms in the warm season (OR, 3.20; 95% CI, 1.05-9.72). Similar results were found in the 2-day (OR, 2.50; 95% CI, 1.47-4.24) and 3-day (OR, 2.53; 95% CI, 1.40-4.55) moving averages. There was no association between outdoor temperature exposure and worsening breathing symptoms overall or in the cold season.

Lower outdoor temperature was associated with worsening bronchitis symptoms instead. In adjusted models, 5 °C lower previous-day outdoor temperature was associated with 1.25 (95% CI, 1.04-1.51) higher odds of worsening bronchitis. Similar associations were found in 2-day (OR, 1.30; 95% CI, 1.06-1.60) and 3-day (OR, 1.42; 95% CI, 1.13-1.78) moving averages. There were no associations between outdoor temperature exposure and bronchitis symptoms in season-stratified models.

The researchers did not find that any associations between temperature exposure and symptoms were explained or confounded by pollutant exposures. Particle matter exposure also did not change any associations between temperature exposure and these outcomes.

Spline plots identified linear-shaped associations between previous-day temperature exposure and breathing symptoms and between previous-day personal and outdoor temperature exposure and bronchitis symptoms. These spline plots identified a non-linear, U-shaped relationship in which the highest quantities of both warmer and colder outdoor temperature exposure were associated with higher odds of breathing symptoms.

This study had a few limitations. Because the study consisted of former smokers with COPD living in an urban environment, the findings of this study may not be generalized to current smokers or patients with COPD living in other settings. The study was performed with only 30 participants, which makes it difficult to generalize the findings to other patients with COPD, such as those with more moderate symptoms. The researchers did not account for characteristics of a participant’s home, such as insulation or heating sources, which may influence the participant’s personal exposure to temperature.

The researchers wrote that higher temperatures year-round may worsen breathing symptoms and cold temperatures may trigger cough and phlegm symptoms in patients with COPD without affecting lung function.

“These findings suggest an opportunity to address personal exposure to warmer temperature as a risk factor for aggravated dyspnoea in the warmer months, and outdoor colder temperatures as a risk factor for increased bronchitis symptoms in COPD throughout the year,” the researchers wrote.

Reference

Scheerens C, Nurhussien L, Aglan A, et al. The impact of personal and outdoor temperature exposure during cold and warm seasons on lung function and respiratory symptoms in COPD. ERJ Open Res. 2022;8:00574-2021. doi:10.1183/23120541.00574-2021