time course of bronchoconstriction induced by dry gas hyperpnea in guinea pigs we examined the effects of hyperpnea duration and abrupt changes in inspired gas heat and water content on the magnitude and time course of hyperpneainduced bronchoconstriction hib in anesthetized mechanically ventilated male hartley guinea pigs in 12 animals subjected to 5 10 and 15 min random order of dry gas isocapnic hyperpnea tidal volume vt 46 ml 150 breathsmin followed by quiet breathing of humidified air vt 23 ml 60 breathsmin severe bronchoconstriction developed only after the cessation of hyperpnea the magnitude of respiratory system resistance rrs increased with the duration of dry gas hyperpnea peak rrs 10 02 18 03 and 23 03 se cmh2oml1s respectively seven other guinea pigs received in random order 10 min of warm humidified gas hyperpnea 10 min of room temperature dry gas hyperpnea and 5 min of dry gas hyperpnea immediately followed by 5 min of warm humidified gas hyperpnea after each hyperpnea period the animal was returned to quiet breathing of humidified gas rrs rose appreciably after the 10 min of dry and 5 min of dry5 min of humidified hyperpnea challenges peak rrs 13 02 and 07 02 cmh2oml1s respectively but not after 10 min of humidified hyperpnea 02 004 cmh2oml1s an additional five animals received 10 min of room temperature dry gas hyperpnea followed by quiet breathing of warm humidified air and 10 min of room temperature dry gas hyperpnea followed by 30 min of warm humidified gas hyperpnea in random orderabstract truncated at 250 words