536 



VETERINARY PHYSIOLOGY 



greater diastolic filling. By allowing access of air into the 

 pericardial sac the differences are abolished. 



B. In man, and this is probably also the case in the 

 imanaesthetised animal, in thoracic breathing the arterial 

 pressure falls during inspiration and rises during expiration, 

 on account of the retention of blood in the distended 

 thorax in inspiration and its expulsion in expiration, and 

 that, in abdominal breathing, the reverse is the case ; 

 inspiration, by pressing on the abdominal vessels and 

 sending more blood on into the arteries, increasing the 

 pressure. 



B. Influence of the Action of the Heart on Respiration. — The 



heart lies in the thorax sur- 

 rounded by the elastic lungs. 

 As it contracts and dilates it 

 must alternately pull upon and 

 compress the lungs, and thus 

 tend to cause an inrush and an 

 outrush of air — the cardio-pneu- 

 matic movements. 



If a simultaneous tracing 

 of the heart-beat and of the 

 movements of the air column be 

 taken, it will be seen that (1) 

 at the beginning of ventricular 

 systole there is a slight outrush 

 of air from the lungs, probably 

 caused by the blow given to the 

 lungs by the suddenness of the systolic movement. (2) This is 

 followed by a marked inrush of air corresponding to the out- 

 flow of blood from the ventricles, and caused by the fact that 

 the contracting ventricles draw on and expand the lungs. 

 (3) Succeeding this is a slower outrush of air corresponding to 

 the active filling of the ventricles during the beginning of 

 ventricular diastole. (4) Lastly, during the period of passive 

 diastole, the cardio-pneumatic movements of air are in 

 abeyance (fig. 217). 



These cardio-pneumatic movements are of importance in 

 two ways. (1) In animals during hibernation, the ordinary 



Fig. 217. — To show Relations of 

 Cardio-pneumatic Movements, 

 A., to tlie Cardiac C\'cle, B. 

 In A. the upstrokes are expira- 

 tory, the downstrokes inspira- 

 tory. 



t 



