Influence of weather and atmospheric pollution on physical activity in patients with COPD

Abstract

Rationale: Information concerning how climate and atmospheric pollutants affects physical activity in COPD patients is lacking and might be valuable in determining when physical activity should be encouraged.

Methods: Seventy-three stable COPD patients recorded on daily diary cards worsening of respiratory symptoms, peak expiratory flow rate, hours spent outside the home and the number of steps taken per day. Pedometry data was recorded on 16,478 days, an average of 267 days per patient (range 29-658). Daily data for atmospheric PM10 and ozone (O3) were obtained for Bloomsbury Square, Central London from the Air Quality Information Archive databases. Daily weather data were obtained for London Heathrow from the British Atmospheric Data Archive.

Results: Colder weather below 22.5 °C, reduced daily step count by 43.3 steps day per °C (95% CI 2.14 to 84.4; p = 0.039) and activity was lower on rainy than dry days (p = 0.002) and on overcast compared to sunny days (p < 0.001). Daily step count was 434 steps per day lower on Sunday than Saturday (p < 0.001) and 353 steps per day lower on Saturday than Friday (p < 0.001). After allowance for these effects, higher O3 levels decreased activity during the whole week (-8 steps/ug/m3; p = 0.005) and at weekends (-7.8 steps/ug/m3; p = 0.032). Whilst, during the week PM10 reduced activity (p = 0.018) but not during the weekend.

Conclusions: Inactivity of COPD patients is greatest on cold, wet and overcast days and at the weekends. This study also provides evidence of an independent effect of atmospheric pollution at high levels.

Fig. 1

Relationship between the average steps per day for each patient and the average hours spent outside the home during the whole week

Fig. 2

Relationship between daily step count and daily temperature; data is averaged in 1 °C intervals. Bars are standard errors

Fig. 3

a Daily step count on Overcast versus Sunny days. b Daily step count on Dry versus Wet days. Data are means ± standard errors of the average for each patient; p-values by paired t-test

Fig. 4

Residuals from a GEE model that included temperature, wind speed, rainfall, hours of sunshine, day length, season and linear trend, plotted against daily PM₁₀ and Ozone (O₃) levels; data are averaged over 10 μg/m³ intervals; bars as ± standard error

Fig. 5

PM₁₀ and O₃ concentrations during the week between 7^th April 2011 and 31 March 2013