The action of morphine,heroin,and codeine on respiration.

Abstract

In a previous series of experiments¹ on cats, it was found that the action of morphine and heroin on respiration was practically limited to a selective depression of the expiratory mechanism, and that codeine produced only stimulation of the spinal cord. These experiments were repeated upon decerebrated and anesthetized dogs, and upon anesthetized rabbits, inducing active expiratory efforts by inhalations of a constant CO₂-air mixture, and recording them by means of a record of intrathoracic pressure, using an esophageal balloon or a pleural cannula; blood pressure and respiratory volume were also recorded.

The results confirm those obtained with cats, namely, morphine and heroin have a selective action on the expiratory mechanism of dogs and rabbits as well as cats, while no constant depressant action could be detected with codeine.

With morphine, dogs showed passive expiration after 2 to 6 mg. per kilo, as a rule, and larger doses had no further effect until circulation was depressed; occasionally very large doses—300 mg. per kilo—reversed this effect and produced increased reflex excitability, but convulsions did not occur, even in decerebrated animelas. Depth of respiration was often increased as the rate was slowed. With rabbits, expiratory depression began with 1 mg. of morphine and was usually complete after 3 to 5 mg., but depth was more frequently decreased than was the case with dogs. Larger doses sometimes reversed this effect, and caused increased reflex excitability, with a return of active expiration, but the circulation of the rabbit was not depressed as much by morphine as was that of the dog or cat.

With heroin, 0.05 mg. per kilo sometimes made expiration completely passive in the dog, and depth of breathing was usually increased as the rate was slowed.