THE PULMONAR Y CIRCULA TION. 1 5 1 



if maintained for only a short period, produced no " back effect " on the 

 pulmonary artery. When, in one experiment, the period of compression 

 was increased, the pressure rose in the pulmonary artery from 24 to 30 

 mm. Hg, while the aortic pressure rose from 90 to 135 mm. Hg. On 

 excitation of the peripheral end of the great splanchnic nerve, the pul- 

 monary arterial tension at first rises very slightly, and at the same time 

 there occurs a great rise of aortic pressure. By continuing the excita- 

 tion the blood congests in the left heart, and the pressure in the 

 pulmonary vessels then rises. 



The devising of experimental means by which purely active changes 

 can be evoked in the pulmonary circulation, and thus the proof of a 

 vasomotor control established, has been extremely difficult; so that 

 some physiologists have gone so far as to maintain that the vascular 

 system of the lungs is not under the direct influence of the central 

 nervous system. The difficulty arises from the susceptibility of the 

 pulmonary circulation to passive changes such as we have discussed, and 

 which arise secondarily to active alterations in the conditions of the 



FIG. 91. Pulmonary and carotid arterial pressures. Curarised flog. 

 Vagi divided. Cord divided at level of seventh dorsal root. Effect 

 of excitation of peripheral end of cord. Bradford and Dean. 



systemic circulation. It is necessary in the experimental investigation 

 of this question to provoke vasomotor changes in the pulmonary circu- 

 lation by the excitation of some portion of the nervous system, while the 

 diastolic filling of the right heart and the systolic output of the left 

 heart remain unaltered by any synchronous variation in the systemic 

 circulation. These postulates have not been carried out in most of the 

 experiments which have been made on the pulmonary vasomotors. 1 



The most exhaustive research on this difficult subject has been 

 carried out by Bradford and Dean. 2 Their evidence in favour of a 

 vasomotor mechanism appears to be conclusive, and is based upon the 

 following experiments : 



1 Brown-Sequard, Lancet, London, 1872 ; Compt. rend. Soc. de Hoi,, Paris, , 



p. 180 ; Badaud, "Ueberden Einfluss des Hirnsauf den Blutdruckin dem Lungen-arterie, 

 Wiirzburg, 1874 ; Couvreur, Compt. rend. Soc. de UoL, Paris, 1889, p. 731 ; Bokai, Jahresb. 

 ii. d. Fortschr. d. Anat. u. Physiol., Leipzig. 1880, Bd. ii. S. 71 ; Henriques, Skandin. Arch. 

 f. Physiol., Leipzig, 1892, Bd. iv. S. 229 ; Waller, Arch. f. Physiol., Leipzig, 1878, S. 025 ; 

 'Lichtheim, " Storungen des Luugenkreislaufes, " Berlin,' 1876; Opencliowski, Arch. f. d. 

 ges. Physiol., Bonn, 1882, Bd. xxvii. S. 233. 



-Bradford and Dean, Journ. Physiol., Cambridge and London, 1894, vol. xvi. p. 34. 



