Effects of central stimulants on onset of diaphragm activity during breath holding

¹ Istituto di Fisiologia umana, Università di Milano, Milano, Italy

The effect of d-methylamphetamine, caffeine, and analeptics on the alveolar Pco₂ during spontaneous breathing and at the onset of diaphragm activity during breath holding has been studied. After d-methylamphetamine the value of alveolar Pco₂ at the onset of diaphragm activity, as well as at the breaking point, is significantly increased, while the ventilation-alveolar Pco₂ relationship is not changed. After caffeine the value of the alveolar Pco₂ at the onset of diaphragm activity, as well as at the breaking point, is significantly decreased and the ventilation-alveolar Pco₂ relationship is significantly shifted to a lower Pco₂. The value of alveolar Pco₂ at onset of diaphragm activity is significantly decreased by prethcamide, increased by pentylenetetrazol, and not affected by dimefline. The ventilation-alveolar Pco₂ relationship was not changed by such analeptics. These data, together with those previously obtained on hypoxia, suggest that factors changing the ventilation-alveolar Pco₂ relationship also affect the onset of diaphragm activity, while the onset of diaphragm activity can be changed without affecting the ventilatory response to CO₂.

Submitted on July 5, 1963