The role of the chemoceptors of the carotid and aortic regions in the production of the Mayer waves.

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Section of the sinus nerves in vagotomised cats suffering from the effects of haemorrhage, abolishes Mayer waves previously evident in the arterial blood pressure record. Blocking of the vagi, by cooling, in bled animals in which the sinus nerves have been previously cut, similarly abolishes the presence of Mayer waves. Carotid occlusion in intact or vagotomised cats suffering from the effects of haemorrhage, causes the appearance of large periodic variations in the arterial blood pressure record. These periodic variations do not appear upon carotid occlusion if the sinus nerves have been sectioned. Similarly if the carotid body chemoceptors have been destroyed by intra-sinusal injection of acetic acid occlusion of the common carotid arteries causes little change in the blood pressure record. The amplitude of the periodic waves of blood pressure caused by clamping the common carotid arteries in animals with intact vagi, is reduced by applying cold-block to the vagus nerves. Occlusion of the external carotid arteries reduces the variations of blood pressure which occur during occlusion of the common carotid arteries. A hypothesis is advanced to explain the causation of the Mayer waves in terms of rhythmic excitation of the chemocep-tor mechanisms occurring in animals suffering from the effects of haemorrhage. Periodic respiration commonly accompanies Mayer waves and in such cases respiration assumes a rhythmicity identical with that of the blood pressure. A similar hypothesis to that given for the Mayer waves may be considered as an explanation for Cheyne-Stokes breathing.