CARBON MONOXIDE EXPOSURE IN COMMUTING CYCLISTS

Abstract

445 In order to assess cyclists' exposure to carbon monoxide (CO), we secured a Drager portable CO monitor to bicycle racks of cyclists who commuted along a commonly used road just prior to scheduled college classes when vehicle traffic was congested. Twenty-two, 10-min cycle trials along the 15% inclined, 1.5-mile route were conducted. CO was recorded every 5 seconds from an air sample within 6 inches from the subject's mouth. Wind velocity ( v) and ambient temperature (T °C) were also measured. CO levels averaged 3.8± 1.1 ppm, with a peak value of 31.8 ppm. Average wind v accounted for only 14%, while average T °C accounted for only 22% of CO total variance. Since CO binds hemoglobin with an ≈ 200-fold greater affinity than does O2, induces a left shift in the oxyhemoglobin dissociation curve, and is clearly detrimental to performance, we are concerned with long-term health implications of repetitive, enhanced CO exposure. Commuting cyclists may increase gas exchange up to 10-fold above resting, and CO has been associated with abnormal EKGs and B echograms, induction of hepatitis B antigen antibodies against heat-shock proteins, respiratory and neural toxicity, immune suppression, increased intracranial pressure, and behavior decrements. Exposures to these levels of CO, after an hour, would result in blood levels of CO comparable to those produced in workers exposed to recommended workplace levels (eg, 25 ppm OSHA; 9 ppm WHO). Since most CO standards were developed for workers in industrial settings, we suggest that new threshold limits and exposure durations be determined for those who exercise vigorously. Cyclists' exposure to CO, only weakly dependent upon wind conditions, is likely more dependent upon turbulent transfer created by car proximity and velocity, in accord with Prandtl-Von Karman turbulent boundary theory. Future studies should attempt to measure CO levels at multiple sites traversing traffic.