Mechanism of respiratory responses to intravenous NaHCO3, HCl, and KCN.

We studied the mechanism by which respiratory responses are produced by rapid injection of NaHCO3, HCl, or KCN into the superior vena cava of lightly anesthetized dogs. To estimate independently circulatory transit time to receptor sites, the solutions were injected at 0 degrees C and their arrival time at the ascending aorta and carotid sinus was detected by thermocouples. All of the ventilatory responses were observed to begin after the substances had reached the ascending aorta and 94% began after the carotid sinus had been reached. The injections were repeated following bilateral vagotomy and/or carotid body resection. Vagotomy produced no significant changes in ventilatory responses, but carotid body resection considerably reduced them. Following both procedures, few ventilatory responses were observed, and the time lag to the onset of the response increased greatly. We conclude that all of the observed ventilatory responses can be accounted for by the known arterial and central chemoreceptors, and that no evidence for pulmonary chemoreceptors was obtained.