Action of Caffeine and Aminophylline as Respiratory Stimulants in Man

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Abstract
The effect on ventilation minute-volumes, cardiac and respiratory rates of 0.25 g. of caffeine and Na benzoate admd. subcut. was observed in 6 subjects while breathing atmospheric air, and 3 and 5% CO2 in O2. This same effect was observed in 5 subjects following the subcut. admn. of 0.25 g. of aminophylline. Caffeine and aminophylline showed a variable effect on ventilation minute-volume with a slight avg. increase when the subject was breathing atmospheric air. The ventilation minute volume was strikingly increased in every case after caffeine when the subject was breathing either 3 or 5% CO2 in O2. After aminophylline the effect was very inconsistent and the avg. effect was not significant. Cardiac rate showed no consistent response to CO2- Both caffeine and aminophylline caused slowing of the cardiac rate. Neither CO2, caffeine, nor the combination caused any significant change in the ecg. No significant change in ecg. was observed following the admn. of aminophylline. In general caffeine and aminophylline caused an increase in respiratory rate. Some practical applications of the observations are mentioned. It is concluded that caffeine acts on the respiratory center by increasing its sensitivity to CO2. The mechanism of the action of aminophylline in the dose used does not appear to be similar to that of caffeine.

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