122 



INFLUENCE OF RESPIRATORY PRESSURE ON THE HEART. 



This inspiratory movement would also be larger were it not for a slight diminution 

 in the volume of the oral and nasal cavities, attended with an expiratory move- 

 ment that takes place at the same time on account of the filling of its arteries 

 oral pulse, nasal pulse. 



3. After the second sound of the heart (at 2), which at times causes a slight 

 depression at the apex of the curve, the blood is dammed back in the thorax, 

 in correspondence with the retrograde wave. As a result a second expiratory 

 movement manifests itself in the descending portion of the curve. 



4. The subsequent secondary wave-movement of the blood from the heart 

 immediately again causes an inspiratory movement of gases, which produces the 

 recoil elevation in the arteries of the body. 



5. More blood now begins to flow into the thorax through the veins with 

 slight fluctuations, and the next heart -beat takes place. 



FIG. 35. Landois' Cardiopneumograph, and Cardiopneumatic Curves Obtained with its Aid. A and B, from 

 man; i and 2 correspond to the period of the first and second heart-sounds; C, curves from the dog; D, 

 showing the instrument in use- 



Pathological. In the healthy human subject a crepitating sound is not rarely 

 heard close to the heart, resulting from the movement of the air in the lungs, 

 brought about by the movement of the heart. If there are near the heart abnor- 

 mally narrow places in the bronchi, through which the respiratory gases are forced, 

 so that they generate a sound or murmur, a fairly loud, sibilant or whistling 

 murmur, known as the pathological Cardiopneumatic murmur, is heard in rare 

 cases. In the presence of cardiac lesions characterized by considerable fluctuations 

 in the quantity of blood in the vessels of the lesser circulation, the cardiopneumatic 

 movement must be quite marked, as, for example, in cases of insufficiency of the 

 pulmonary and mitral valves. 



INFLUENCE OF THE RESPIRATORY PRESSURE ON THE DILA- 

 TATION AND CONTRACTION OF THE HEART. 



The variations in pressure to which all the parts within the thorax 

 are subjected by its inspiratory expansion and expiratory contraction 

 exert a visible influence on the diastole and systole of the heart. 



The conditions in various positions of the resting thorax with the 

 glottis open will be considered first. The diastolic dilatation of the 

 cavity of the heart is brought about by the elastic traction of the lungs, 

 as well as by the inflow of venous blood and the elastic stretching of the 

 relaxing muscular walls. This traction is greater in proportion as the 



