HG THE VASCULAR SYSTEM 



always falls when the patient is told to take a deep breath, and 

 thus what has been termed the pulsus paradoxus and considered 

 of pathological import, turns out to be quite a normal event. 



In animals, says Lewis, under deep anesthesia, the abdomen 

 plays no part in the production of respiratory curves. The in- 

 spiratory rise is due to the lessened pressure in the pericardium 

 and consequent increased filling of the heart. It is abolished by 

 allowing free access of atmospheric air to the pericardial sac. The 

 varying intra-pleural pressure affects intimately the filling of the 

 heart, while its influence on the resistance and capacity of the 

 pulmonary vascular area is a matter of assumption rather than of 

 experimental proof. We are at present, says Lewis, justified by 

 experiment in ascribing the inspiratory rise in animals on intercostal 

 breathing to the effect on the heart only. 



Tigerstedt found that ligation of the vessels of the left lung, 

 ^out of thirty-one observations, produced in eighteen no noticeable 

 effect on the output per second of the heart. In eleven cases it 

 produced a decrease of 6 to 10 per cent., and in two cases a decrease 

 of 18 to 20 per cent. In twenty- three cases the arterial pressure 

 was unaltered by this operation, in seven it was decreased 

 C to 10 per cent., and in one case over 10 per cent. Thus the 

 pulmonary circuit can be shut off to a very large extent at least 

 in the animal with artificial respiration and the remainder 

 suffice to deliver an unlessened quantity of blood to the heart. 

 Tigerstedt's observations also show that the arterial pressure may 

 sometimes remain constant when the output of the heart varies 

 considerably ; the explanation of this is that the arterial system 

 contracts down on the blood that it contains. 



In Valsalva's experiment a deep expiration with the mouth 

 and nose shut the abdominal pressure rises very greatly, and 

 this is the chief cause of the rise of arterial pressure which then 

 occurs. If a stiff -walled rubber tube is used as a rectal sound, 

 and is connected to a manometer, an estimate of intra-abdominal 

 pressure may be obtained, and this can be compared with the 

 expiratory pressure obtained by expiring against a mercurial 

 manometer. In one case the rectal pressure rose to 94 mm. Hg, 

 and the tracheal pressure to 87 mm. Hg. The same conditions 

 occur in coughing. 



In deep abdominal breathing the rectal pressure may rise to 

 30 mm. Hg, and frequently shows a range of 20 mm. Hg, a fact 



