Airway responsiveness measured by barometric plethysmography in guinea pigs

Barometric plethysmography has become an increasingly used method to indirectly measure respiratory function in unrestrained freely-moving animals. This technique has been criticized because of physiological uncertainty of its major index, the enhanced pause (Penh). Moreover, a recent study raises concerns that during histamine challenges part of the Penh response could be produced by upper airways (nasal) responses. In this study we compared airway responsiveness measured by barometric plethysmography and total lung resistance (RL) in guinea pigs, and evaluated the role of upper airways during Penh measurement. Our results showed that intravenous acetylcholine or histamine caused a dose-dependent increase of the Penh values in non-anesthetized guinea pigs, which were correlated with RL values obtained in separate groups of anesthetized animals. In anesthetized but spontaneously breathing guinea pigs intravenous acetylcholine or histamine also produced a dose-dependent increment of Penh, which was similar regardless if guinea pigs breathed through the nose or through a tracheal tube. Our results suggest that, independently of the physiological meaning of Penh, this index seems to be a useful indirect measurement for evaluating airway responsiveness to intravenous agonists in guinea pigs, and that nasal passage seems not to be involved in this measurement.