1867.] On the Influence of Respiration on Circulation, 395 



distension of the tlioracic veins, and to the violence of the expiratory 

 movements. 



Theoretical exposition of the mechanical influence of the respiratory 

 movements on the circulation. — (1) It has been demonstrated by Bonders 

 that the elastic contents of the chest have at all times a tendency to shrink 

 to a smaller bulk than that of the cavity in which they are contained, so 

 that the viscera within the thorax are constantly distended in a degree 

 which varies according to its ever-varying capacity. As, however, they 

 are not equally elastic, they yield to this distension unequally. When the 

 chest enlarges, the lungs yield most, the veins and heart, in a state of 

 relaxation, next ; the contracting heart and the arteries scarcely expand at 

 all. (2) If the veins contained air and communicated with the atmo- 

 sphere, they would fill as rapidly as the lungs ; actually their expansion is 

 much slower. Hence the first effect of inspiration is to increase the pro- 

 portion of thoracic space occupied by the lungs, by which they become 

 relatively m.ore distended than the other organs. So soon, however, as the 

 veins and auricles have time to fill, equilibrium is m.ore or less restored. 

 (3) Hence it follows {a) that the dilatation of the chest in inspiration 

 aids the expansion of the heart during diastole and of the thoracic veins ; 

 and (h) that these events cannot occur simultaneously with their cause, 

 but must follow at an interval varying according to the condition of the 

 circulation. (4) Other things being eq^^al, the force and frequency of the 

 contractions of the heart are increased by whatever causes accelerate its 

 diastolic impletion. The more rapidly the cavities fill the shorter must 

 be its period of relaxation, the more vigorous its systole, and consequently 

 the greater the arterial pressure. (5) The effect of thoracic expansion on 

 the intra-thoracic veins varies both as regards its degree and the time of 

 its occurrence. Both kinds of variation depend on the velocity of the 

 circulation and the pressure existing in the veins outside of the chest. 

 When the systemic veins are distended, the circulation rapid, and the 

 arterial resistance in consequence diminished, the heart almost empties 

 itself at each contraction, and the expansion of the chest fills the thoracic 

 veins and the relaxed heart with great rapidity. In the opposite case, 

 when the systemic veins are comparative!}'" empty, the cavities of the heart 

 fill slowly, and discharge themselves imperfectly on account of the excessive 

 arterial resistance. (6) Hence the effect of inspiration in facilitating the 

 diastolic impletion of the auricles, and consequently in increasing the 

 frequency and force of the hearts action, varies directly as the velocity 

 of the circulation, inversely as the arterial pressure. 



Conclusions. — 1. In natural breathing the influence exercised by the 

 thoracic movements on the heart is entirely mechanical. So long as the 

 respiration is tranquil, variations of air-pressure in the bronchial tubes and 

 vesicles of the lungs do not materially affect the arterial pressure ; but 

 violent expiratory movements are accompanied by simultaneous increase of 

 vascular tension. 



