RESPIRATORY UNDULATIONS. 



399 



respiratory undulations may be due to a rhythmic rise and fall of the 

 activity of the vasomotor centre, synchronous, like that of the cardio- 

 inhibitory centre, with the respiratory movements. There can, however, be 

 no doubt that the respiratory variations in blood-pressure are due to the 

 mechanical conditions discussed above, and that vasomotor influences inter- 

 vene but little if at all. 



FIG. 109. 



Blood-pressure Curve of a Rabbit, Recorded on a Slowly Moving Surface, to show Traube- 

 Hering Curves. (The curve was described not by means of a mercury manometer, but by an in- 

 strument similar to but not identical with Fick's spring kymograph.) In each heart-beat the 

 upward and downward strokes are very close together, but may be easily distinguished by the 

 help of a lens. The undulations of the next order are those of respiration. The wider sweeps 

 are the Traube-Hering curves, of which two complete curves and portions of two others are 

 shown. Each Traube-Hering curve comprises about nine respiratory curves, and each respiratory . 

 curve about the same number of heart-beats. 



331. The further general effects, similar to the above, on the vascular 

 system of deficient arterialization of the blood may be studied by taking a 

 blood-pressure tracing from the carotid or other artery of an animal while 

 the interference with respiration is pushed on to a fatal asphyxia. During 

 the first and second stages of the asphyxia the blood-pressure rises rapidly, 

 attaining a height far above the normal. During the third stage it falls 

 even more rapidly, repassing the normal and becoming nil as death ensues. 

 If the animal, no urari having been given, is breathing of itself, and if, as 

 usually is the case, the asphyxia is brought about by occlusion of the trachea, 

 so that the mechanical effects of the respiratory movements are exaggerated 

 by the air being unable to enter the chest, the respiratory undulations of 

 the pressure-curve due to the mechanical causes discussed above are, espe- 

 cially during the first stage, extensive, abrupt, and irregular, the inspiratory 

 movements being accompanied by a conspicuous fall of pressure. When 

 the animal has been previously placed under urari, so that the respiratory 

 impulses cannot manifest themselves by any muscular movements, the rise 

 of the pressure-curve, as we have already said, is at first steady and un- 

 broken, but after a variable period Traube's curves make their appearance. 

 As during the third stage the pressure sinks, these undulations pass away. 



The heart-beats are at first somewhat quickened, but speedily become 

 slow, at the same time, as we have seen, not notably losing force, so that the 

 pulse-curves on the tracing are exceedingly bold and striking. But the 

 boldness of the curve of the mercury manometer is, it must be remembered, 

 partly the mere result of the slowness of the rhythm ; the mercury has time 

 to fall largely between each two beats. (Fig. 108, 3 and 4.) Even while 

 the blood-pressure is sinking, and when the cardiac stroke is now certainly 

 lessening in vigor, the slowness of the cardiac rhythm is still sufficient to 

 maintain somewhat these characters of the curve. The strokes at last, how- 



