Ambient carbon monoxide levels and acute cardiorespiratory complaints: an exploratory study

Over a 92-day seasonally excessive period of ambient carbon monoxide (CO), chief cardiorespiratory complaints (CRC) of a nontraumatic origin were identified from each of 8,556 patient encounters at the Emergency Room of Colorado General Hospital. Excessive numbers of CRC were seen above a CO level of 5 ppm for the 24-hour mean and 11 ppm for the one hour mean maximum ambient CO (p less than 0.05 for both). Increasing relative risk was shown by comparing daily numbers of CRC with its mean in two-day trend analyses with both ambient CO measures above and below these thresholds. Other ambient pollutants were generally low during the winter period studies. These findings suggest an association between health effects and lower levels of CO than has been previously reported.