Responses of healthy young males to fine-particle exposure are modified by exercise habits: a panel study

Aerobic exercise benefits health but increases inhalation of fine particles (PM_2.5) in ambient air. Acute cardiopulmonary responses to PM_2.5 exposure in individuals with different exercise habits, especially in areas with severe air pollution, are not well understood.

To examine acute cardiopulmonary responses to PM_2.5 exposure modified by exercise habits, a panel of 20 healthy non-smoking male subjects, recruited in Beijing, China, completed seven visits. The exercise frequency per week and preferred exercise place were recorded using a baseline questionnaire to describe exercise habits. Fractional exhaled nitric oxide (FeNO), cytokines in exhaled breath condensate, blood pressure, and pulse-wave analysis (PWA) indices were measured during each visit as biomarkers of acute cardiopulmonary responses. The hourly average mass concentration of PM_2.5 and black carbon (BC), and the number concentrations of ultrafine particles (UFP) and accumulation mode particles (AMP) were monitored throughout the follow-up period at an outdoor fixed monitoring station beginning 14 days prior to each visit. Linear mixed-effects models were used to evaluate the associations between acute changes in biomarker levels and exposure to PM_2.5 and its constituents. The primary aim was to assess the modification of long-term exercise habits on these associations.

FeNO concentration, systolic blood pressure, ejection duration, aortic augmentation pressure, and aortic pressure index were positively associated with exposure to PM_2.5 and its constituents. However, no associations with cytokine levels or diastolic blood pressure were observed. In a stratified analysis, we found that acute cardiopulmonary responses were modified by exercise habit. Specifically, the interquartile ranges (IQR) of increases in the 6-12-h moving average (MA) PM_2.5 and AMP exposure were associated with 19-21% and 24-26% increases in FeNO, respectively, in subjects with high exercise frequency; these associations were significantly stronger than those in subjects with low exercise frequency. An IQR increase in 3-11-d MA AMP exposure was associated with a 10-26% increase in aortic augmentation pressure in subjects with low exercise frequency; this association was significantly stronger than that in subjects with high exercise frequency. An IQR increase in 9-13-d MA UFP exposure was associated with a 13-17% increase in aortic augmentation pressure in subjects who preferred outdoor exercise; this association was stronger than that in subjects who preferred indoor exercise.

In highly polluted areas, frequent exercise might protect against PM_2.5-associated arterial stiffness but exacerbate airway inflammation.