128 THE MECHANISM OF THE CIRCULATION. 



consequence of the paralysis of the thoracic and the abdominal wall, the 

 respiratory undulations on the arterial tracing are greatly reduced. 



According to Marey, the rise of arterial pressure in man is inspiratory when 

 the breathing is diaphragmatic, and expiratory when the breathing is thoracic 

 in type. In the rabbit, an animal which breathes rapidly, the respiratory 

 waves of aortic pressure can be reversed in time by turning the animal alter- 

 nately on its back and on to its belly. 



Heger and Spehl 1 split the sternum without opening the pleural cavities, 

 and passed a ligature round the aorta and pulmonary arteries. In one animal, 

 they tightened this ligature in the inspiratory phase, and in a second animal in 

 the period of expiration. The lungs were in each case excised, and the 

 amount of blood therein estimated. They found that in the phase of natural 

 inspiration, T V to -^ of the whole blood in the body was contained in the 

 lungs ; in the phase of expiration, T ^ to y 1 ^. On the other hand, when the 

 lungs were artificially blown out, only -^ of the whole blood was found 

 therein. The amount of blood found in the lungs in the state of deepest 

 expiration may be called the residual blood. The difference between this 

 amount, and that found in ordinary expiration, will then be known as the 

 supplemental blood, while the increase of the volume of blood in ordinary 

 inspiration is called the tidal blood. Lastly, the difference between the 

 volume of blood in ordinary inspiration, and the deepest inspiration, may 

 be named the complemented blood. Thus, the changes in blood volume 

 can be brought under the same nomenclature as the changes in the volume of 

 intra-pulmonary air. In natural breathing, the air and the blood volume 

 change together, and in the same way. 



The effect of raising the intrathoracic pressure can be studied in 

 animals by placing the tracheal tube in connection with a chamber in 

 which the pressure of the air can be suddenly raised or lowered. On 

 maintaining the intra-pulmonary pressure at a certain positive height, the 

 arterial pressure falls to zero, and the blood congests in the veins. Con- 

 versely, on lowering the intra-pulmonary pressure considerably, the arterial 

 tension is increased. 2 These effects are similar to, but more pronounced than, 

 those produced by expansion and collapse of the lungs in ordinary artificial 

 respiration. 



The breathing of compressed or rarefied air has been applied as a thera- 

 peutic agent by means of pneumatic cabinets. 3 It is found that 



1. If the expiratory air be conducted by a tracheal tube into compressed 

 air, while the inspiratory air be drawn from rarefied air, then both the normal 

 expiratory and inspiratory effects are heightened, and the respiratory waves on 

 the arterial trace are magnified. 4 



2. If, on the other hand, the inspiratory air be drawn from compressed 

 air, while the expiratory air be conducted into rarefied air, then the normal 

 effects are opposed, and the respiratory waves of arterial tension are lessened. 

 By the inspiration of highly compressed air through a tracheal tube the 

 circulation is rendered difficult, owing to the rise of intra-pulmonary pressure. 

 In consequence, an asphyxial rise of arterial tension may take place, arising 

 from the lack of oxygenation of the bulbar centres. 



3. If the lungs be supplied with air at the normal atmospheric pressure 

 through a tracheal tube, and the body be exposed to a lessened pressure in the 

 pneumatic cabinet, then the arterial pressure falls very considerably. Thus 

 an extrathoracic pressure of -27 mm. Hg produced a fall of arterial pressure 

 equal to 120 mm. Hg. In this condition, the intra-pulmonary pressure is 



1 Spehl, " De la repartition clu sang, etc.," Bruxelles, 1883. 



2 Einbrodt, loc. cit. 



3 Waldenburg, BerL klin. Wchnschr., 1873, S. 465. 



4 Zuntz, Arch.f. d. ges. Physiol., Bonn, 1878, Bd. xvii. S. 374. 



