TRAUBE-HERING CURVES. 171 



on the heart, or on any local peripheral nervous mechanism, or on the 

 muscular fibres of the arteries. This experiment shows that it is 

 the vaso-motor centre which is specially acted upon by the venous 

 blood.] 



[Traube-Hering Curves. The following experiment proves that the 

 varying activity of the vaso-motor centre suffices to produce undula- 

 tions in the blood-pressure tracing. Take a dog, curarise it, expose 

 both vagi and establish artificial respiration ; then estimate the blood- 

 pressure in the carotid. After section of the vagi, the heart will 

 continue to beat more rapidly, but it will be undisturbed by the 

 cardio-inhibitory centre. Thus the central factor in the causation of 

 the blood-pressure remains constant. Suddenly interrupt the respi- 

 ration and, as already stated, the blood-pressure will rise steadily and 

 uniformly, owing to the stimulation of the vaso-motor centre by the 

 venous blood. In this case the peripheral factor or state of tension of 

 the small arteries throughout the body is influenced by the condition 

 of the nerve-centre which controls their action. After a time, the blood- 

 pressure tracing shows a series of bold curves higher than the original 

 tracing. These can only be due to an alteration in the state of the 

 small arteries, brought about by a condition of rhythmical activity of 

 the vaso-motor centre. These curves were described and figured by 

 Traube, and are called the Traube or Traube-Heriug curves. As in other 

 conditions, stimulation gives place to exhaustion, and soon the venous 

 blood paralyses the vaso-motor centre and the small arteries relax, 

 blood flows freely out of the larger arteries, and the blood-pressure 

 rapidly sinks. Variations in the blood-pressure have been observed 

 after a mechanical pump has been substituted for the heart, i.e., after 

 all respiratory movements have been set aside, so that the only factor 

 which would account for the phenomena of the Traube-Hering curves 

 is the variation in the peripheral resistance in the small arteries, 

 determined by the condition of the vaso-motor centre.] 



The respiratory undulations of the blood-pressure become more pronounced the 

 greater the force of the respirations, which produce greater variations of the intra- 

 thoracic pressure. In man, the diminution of the pressure within the trachea is 

 1 mm. Hg. during tranquil inspiration, while during forced respiration, when the 

 respiratory passage is closed, it may be 57 mm. Conversely, during ordinary 

 expiration, the pressure is increased within the trachea 2-3 mm. Hg., while during 

 forced expiration, owing to the compression of the abdominal muscles, it may reach 

 87 mm. Hg. 



The increase of the blood-pressure during inspiration, as well as the 

 fall during expiration, must in part depend upon the pressure within 

 the abdomen. As the diaphragm descends during inspiration, it 

 presses upon the abdominal contents, including the abdominal vessels, 



