BLOOD-PRESSURE IN THE PULMONARY ARTERY. 179 



the nervous system. The vaso-motor system has much less effect upon 

 the pulmonary blood-vessels than upon those of the systemic circulation 

 (Badoud, Hofmokl, Lichtheim). The compensation seems to be due 

 chiefly to the great distensibility and dilatation of the pulmonary vessels 

 (Lichtheim)]. 



We know little of the effect of physiological conditions upon the 

 pulmonary artery. According to Lichtheim suspension of the respiration 

 causes an increase of the pressure. [In one experiment he found that 

 pressure within the pulmonary artery was increased, while it was not 

 increased in the carotid, and he regards this experiment as proving 

 the existence of vaso-motor nerves in the lung.] Morel found that 

 electrical and mechanical stimulation of the abdominal organs caused a 

 considerable rise of pressure in the pulmonary artery (dog). 



During the act of great straining, the blood at first flows rapidly out of the pul- 

 monary veins and afterwards ceases to flow, because the inflow of blood into 

 the pulmonary vessels is interfered with. As soon as the straining ceases, blood 

 flows rapidly into the pulmonary vessels (Lalesque). 



Severini found that the blood-stream through the lungs is greater and more rapid 

 when the lungs are filled with air rich in C0 2 than when the air within them 

 is rich in O. He supposes that these gases act upon the vascular ganglia within 

 the lung, and thus affect the diameter of the vessels. 



Pathological. Increase of the pressure within the area of the pulmonary artery 

 occurs frequently in man, in certain cases of heart disease. In these cases the 

 second pulmonary sound is always accentuated, while the elevation caused thereby 

 in the cardiogram is always more marked and occurs earlier ( 52). 



[Influence of the Nervous System. The pulmonary circulation 

 is much less dependent on the nervous system than the systemic 

 circulation. Very considerable variations of the blood-pressure within 

 the other parts of the body may occur, while the pressure within the 

 right heart and pulmonary artery is but slightly affected thereby. The 

 pressure is increased by electrical stimulation of the medulla oblongata, 

 and it falls when the medulla is destroyed. Section and stimulation 

 of the central or peripheral ends of the vagi, stimulation of the 

 splanchnics, and of the central end of the sciatic, have but a minimal 

 influence on the pressure of the pulmonary artery (Aubert).] 



89. Measurement of the Velocity of the Blood-Stream. 



Methods, (i.) A. W. Volkmann's Haemadromometer. A glass tube of the 



shape of a hair-pin, 60-130 ctm. long and 2 or 3 mm. broad, with a scale 

 etched on it, or attached to it, is fixed to a metallic basal plate, B, so that each limb 

 passes to a stop-cock with three channels. The basal plate is perforated along its 

 length, and carries at each end short cannulse, c, c, which are tied into the ends 

 of a divided artery. The whole apparatus is first filled with water [or, better, 



