THE INFLUENCE OF RESPIRATION 



127 



pulmonary vessels dilate. At first the blood collects in the dilated 

 vessels ; subsequently the blood-now is increased. If the thorax be 

 closed, the intrathoracic pressure is increased when the lungs are 

 expanded, and decreased when the lungs are collapsed. The diastolic 

 filling of the heart is diminished by expansion, thus the pressure 

 in the pulmonary artery falls. It follows from the above that, with a 

 slow rate of artificial respiration, the maximal pressure is obtained 

 in the aorta at the commencement of expansion, the minimal at the 

 beginning of collapse. If the rate of artificial respiration he rapid, 

 the first effect only has time to appear in either case ; that is to say, the 

 expulsion of the blood from the pulmonary capillaries in expansion, and 

 the retention of the same in collapse. In consequence, the pressure rises 

 in inspiration and falls in expiration. 1 



In natural respiration the results are diametrically opposite. 

 During inspiration, the intrathoracic pressure falls, the intra-pulmonary 

 pressure exerted on the pulmonary capillaries becomes less, the sectional 

 area of these capillaries increases, the diastolic filling of the heart is 

 favoured. The blood at first fills up the enlarged pulmonary vessels, 



Fig. 81. — Aortic pressure. Artificial respiration, y-e, effect of clamping trachea, the 

 lungs being expanded ; e, x', i, effect of removing clamp. — Kowalewsky. 



and subsequently flows in increased volume. Thus the pulmonary 

 arterial pressure falls, 2 while the aortic tension rises after a preliminary 

 fall. During expiration the intra-pulmonary pressure increases, the 

 sectional area of the pulmonary vessels decreases, the intrathoracic 

 pressure rises, and the diastolic filling of the heart is lessened. The 

 blood is at first expelled from the pulmonary vessels, and subsequently 

 flows in diminished volume. Thus the pulmonary arterial pressure 

 rises, while the aortic tension falls after a preliminary rise. These 

 typical results of natural breathing can be observed in the most marked 

 form when the respiration is slow and at the same time deep ; for 

 example, after section of the vagi. In rapid breathing only the first 

 phase has time to appear in either case ; that is to say, the retention 

 of the blood in the pulmonary capillaries in inspiration, and the 

 expulsion of the same in expiration. 



In addition to the influence of the thoracic aspiration, the diastolic 

 filling of the heart is aided by the inspiratory descent of the diaphragm, 

 and expiratory contraction of the abdominal muscles, both of which 

 compress the abdominal contents and drive the blood into the heart. 

 Eespiration acts both as a suction and a force pump. 



After section of the spinal cord at the first dorsal vertebra, in 



1 Kowalewsky, Arch. f. Physiol., Leipzig, 1877, S. 419 ct seq. 

 2 Talma, Arch. f. d. gcs. Physiol., Bonn, 1882, Bd. xxix. S. 332. 



