The effect of atropine and morphine on respiration

It has been accepted as a fact that atropine is a respiratory stimulant which, when it is given to a patient in combination with morphine, reduces the amount of respiratory depression caused by morphine (Wangeman and Hawk, 1942). This stems from the work of Waters (1938) who concluded from measurements of respiratory minute-volume, respiratory rate and tidal exchange that morphine was a respiratory depressant and atropine a respiratory stimulant. However, this was only a casual report and no data were given. The studies reported here indicate that 0.6 mgm. of atropine is not a direct respiratory stimulant. Since these drugs are commonly used for premedication in anesthesia the respiratory effects of atropine, morphine, and atropine plus morphine have been reevaluated in terms of the alveolar ventilation-alveolar Pjo2 curve. Greater understanding of respiratory physiology has made it clear that a more accurate evaluation of either the stimulating or depressing effect of a drug can be based on the alveolar ventilation response to measured values of alveolar P02 rather than by simple measurements of respiratory minute-volume, rate or tidal exchange