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In nine cats and nine human subjects anesthetized with alfaxalone, respiratory activity and tracheal pressure were recorded prior to and during occlusion of the airway at end inspiration or end expiration. Lung inflations at the end of expiration were also performed. In addition, the ventilatory pattern was analyzed during hypercapnia. The results show that occlusions at the end of inspiration or inflations provoked an apnea in both cats and humans. However, concomitant with increases in tidal volume during hypercapnia, inspiratory duration decreased in cats and did not change in human subjects. These results indicate that the Breuer-Hering reflex, which delays the onset of inspiration during inflation was equally operative in cats and humans. In contrast, the "Breuer-Hering threshold curve," which accounts for the off-switch" of inspiration was different in cats and humans. Thus, in summary, the Breuer-Hering inflation reflex is operative in human subjects, but it does not seem to be involved in the control of the inspiratory off-switch mechanism during increases respiratory activity resulting from hypercapnia.

The bronchodilator effects of ketamine were examined in human bronchial preparations contracted maximally with histamine, acetylcholine, barium chloride or potassium chloride. Antagonism between ketamine and either histamine or acetylcholine was examined also. Ketamine caused bronchial relaxation irrespective of the constricting agent, and exerted a partial and non-competitive antagonism to histamine and acetylcholine. Propranolol and indomethacin did not inhibit the effect of ketamine, excluding the involvement of beta activation and of prostaglandins.