344 



THE HUMAN BODY 



above the pressure in the auricles; during this time, again, the 

 valves of the heart are all shut. 



Effects of Valvular Insufficiency. The commonest heart 

 troubles are due to failure of one or other of the valves to close 

 perfectly. The mechanical effect of such inefficiency is, of course, a 

 back rush of blood through the leaky valve. The effects on the 

 Body at large will depend on which valve is inefficient. Leakage 

 of the semilunars means a return into the ventricle of part of the 

 blood just pumped out. The circulation is to that extent less 

 effectively maintained. The heart usually compensates for this 

 defect by muscular growth (hypertrophy) by which it becomes 

 enough more powerful than normally to make up for the lessened 

 efficiency. Leakage of an auriculoventricular valve is much more 

 serious because it permits a jet of blood to be driven backward 

 into the veins at each heart-beat under the driving force of the 

 powerful ventricular contraction. The small veins and capillaries 

 are not adapted to receive such a hammering and are injured 

 thereby. If the leaky valve is the mitral the lung capillaries are 

 the ones affected. If the tricuspid is inefficient the backward surge 

 makes itself felt in distant organs. Kidney impairment is a com- 

 mon sequel to this type of valvular disease. Inflammatory rheuma- 

 tism frequently brings on valve trouble. In fact the danger of this 

 outcome is so great that every pains should be taken to avoid it, by 

 giving the patient the best of care and treatment. 



Diagram of the Events of a Cardiac Cycle. In the following 

 table the phenomena of the heart's beat are represented with ref- 

 erence to the changes of form which are seen on an exposed working 

 heart. Events in the same vertical column occur simultaneously; 

 on the same horizontal line, from left to right, successively. 



