Hyperventilation-induced bronchoconstriction in guinea pigs

The purpose of this study was to investigate the pulmonary effects of hyperventilation in anesthetized, mechanically ventilated guinea pigs. Airway resistance (Raw), dynamic lung compliance (CDyn), blood pressure (BP), heart rate (HR), arterial blood gases (PaO2, PaCO2), pH and arterial plasma HCO3- were measured before and after a 10-min period of hyperventilation produced by increasing the respiratory rate from 60 to 120 breaths/min while maintaining tidal volume at 4 ml. There was a significant increase in Raw and decrease in CDyn lasting up to 20 min after hyperventilation was stopped with no change in BP and HR. PaO2 was reduced from 109 +/- 3 mm Hg before to 53 +/- 7 mm Hg at 5 min after hyperventilation. The Raw and CDyn changes were prevented and reversed with the bronchodilators salbutamol and aminophylline indicating that reversible bronchospasms are induced in guinea pigs following a period of hyperventilation. Additional studies demonstrated that the pulmonary mechanical responses to hyperventilation were not changed by vagotomy, ventilation with high CO2 or by pretreatment with chlorpheniramine, methysergide, atropine, indomethacin, FPL 55712 or calcium-influx blockers. These results indicate that neither vagal reflexes, airway hypocapnia, receptors of histamine, serotonin, acetylcholine nor the products of arachidonic acid metabolism were involved in hyperventilation-induced bronchospasm in guinea pigs.