THE PULMONARY CIRCULATION. 



*53 



by a more gradual fall ; (2) a considerable rise in the pulmonary artery, 

 synchronous with the commencement of the aortic rise but overlasting 

 the latter, and followed by a gradual fall ; (3) a great rise in the 

 pulmonary venous pressure synchronous with the aortic fall. 



After complete division of the spinal cord at the level of the sixth 

 or seventh dorsal root, asphyxia produced the same rise in the pulmonary 



Carotid 



123 771 771 . 



Pulmonary 



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 /4mm . 



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Fig. 93. — Pulmonary and carotid arterial pressures. Curarised dog. Spinal cord divided 

 at level of sixth dorsal root. Effect of asphyxia. — Bradford and Dean. 



arterial pressure, and this was now accompanied by but a slight rise 

 in aortic pressure (Fig. 93). 



Thus in one case the aortic pressure rose from 117 to 123 mm. Hg, 

 while the tension in the pulmonary artery rose from 14 to 26 mm. Hg. 

 The rise of pulmonary venous pressure in the last stage of asphyxia 

 is due to failure of the left heart, and a consequent decrease in the 

 systolic output. In all these experiments the animals were curarised as 



Fig. 94. — Pressure curves of pulmonary artery, left auricle, and femoral artery. Effect 

 of excitation of central end of crural nerve. — Franeois-Franck. 



well as anaesthetised, in order to eliminate all changes in the circulation 

 which might arise from muscular movements. Turning to the effects 

 of reflex excitation of the pulmonary vasomotor mechanism, Bradford 

 and Dean noted that stimulation of the central end of any posterior root 

 in the upper thoracic region caused a rise both in aortic and pulmonary 

 arterial pressure, but the rise was proportionately greater in the latter. 



