Dose‐response relationship of ozone‐induced airway hyperresponsiveness in unanesthetized guinea pigs

The effect of ozone dose (the product of ozone concentration and exposure time) on airway responsiveness was examined in unanesthetized, spontaneously breathing guinea pigs. Airway responsiveness was assessed by measuring specific airway resistance (sRaw) as a function of increasing concentration of inhaled methacholine (Mch) aerosol (the concentration of Mch required in order to double the baseline sRaw: PC200Mch). The airway responsiveness was measured before and at 5 min, 5 h, and 24 h after exposure. A 30‐min exposure to 1 ppm ozone (dose 30 ppm‐min) did not change PC200Mch at any time after exposure. Both a 90‐min exposure to 1 ppm ozone and a 30‐min exposure to 3 ppm ozone, which are identical in terms of ozone dose (90 ppm·min), decreased PC200Mch to a similar degree. A 120‐min exposure to 3 ppm ozone (360 ppm · min) produced a much greater decrease of PC200Mch at 5 min and 5 h after exposure, compared with low‐dose exposure. There was a significant correlation between ozone dose and the change in ...