Dr. Nadziejko and her colleagues at the New York University School of Medicine evaluated the effects of exposing healthy rats to concentrated ambient particles (CAPs) and changes in blood coagulation parameters. The investigators measured platelet number, blood cells counts, and levels of fibrinogen, thrombin-antithrombin complex, tissue plasminogen activator, plasminogen activator inhibitor, and factor VII of rats that were exposed to concentrated New York City particles and filtered air for 6 hours. Blood samples were obtained before and after exposure using an indwelling catheter.