Association between air pollution and obstructive sleep apnea in terms of respiratory event frequency and lung-to-finger circulation time

Air pollutant exposure has been shown to exacerbate obstructive sleep apnea (OSA) manifestations, such as increased respiratory episodes and intermittent oxygen desaturation. However, most studies have focused on episode frequency rather than duration. This study investigated the associations between air pollution and OSA manifestations using both frequency-based indices and the duration-based marker lung-to-finger circulation time (LFCT). Polysomnography data from 820 individuals with suspected OSA (mild-to-moderate: n = 224; severe: n = 596) were analyzed. Sleep disorder indices included the apnea–hypopnea index (AHI), oxygen desaturation index (ODI), arousal index, and mean LFCT. A novel composite metric, respiratory event response time area (RERTA), defined as the square root of the product of LFCT and AHI, was introduced to evaluate the interplay between frequency and duration. Air pollutant exposure was estimated using data from monitoring stations within 4 km of the registered residences of the study cohort. Multivariable Poisson regression models were employed to assess short-term (1-month) and long-term (1-year) exposure effects. Short-term PM_2.5 and NO₂ exposure were significantly associated with increased AHI, ODI, arousal index, and reduced LFCT. Long-term exposure to PM_2.5, PM₁₀, and NO₂ was associated with increased AHI and ODI, while PM_2.5 and PM₁₀ were linked to reduced LFCT. Both short- and long-term O₃ exposure were associated with increased AHI and ODI. PM_2.5 and O₃ (short-term) were positively associated with RERTA. These findings suggest that air pollution exacerbates OSA by increasing episode frequency and accelerating compensatory responses, thereby elevating cardiopulmonary burden as reflected by RERTA.