254 HUMAN PHYSIOLOGY 



The tension of the pulse varies directly with the force of 

 the heart and with the peripheral resistance. The first 

 statement is so obvious as to require no amplification. It is 

 also clear that if the peripheral resistance is low so that blood 

 can easily be forced out of the arteries into the capillaries, 

 the arterial wall will not be so forcibly expanded as when 

 the resistance to outflow is great. Hence a high tension 

 pulse is indicative of a strongly acting heart with constriction 

 of the peripheral vessels. It is well seen during the shivering 

 fit which so frequently precedes a febrile attack, since at that 

 time the peripheral vessels are constricted and the heart's 

 action excited. The tension of the pulse wave must not be 

 confused with the mean arterial pressure. 



oth. The form of the pulse wave may be investigated by 

 means of the finger alone or by means of the sphygmograph. 

 The points to be observed are 



(1) Does the wave come up suddenly under the finger ? 

 In the pulsus celer (or active pulse) it does so ; in the 

 pulsus tardus, on the other hand, it comes up slowly. The 

 former condition is indicative of an actively acting heart 

 with no great peripheral resistance the latter indicates that 

 the heart's action is weak in relationship to the arterial blood 

 pressure. 



(2) Does the wave fall slowly or rapidly ? Normally the 

 fall should not be so sudden as the ascent. When the 

 aortic valves are not closed properly the descent becomes 

 very rapid. 



(3) Are there any secondary waves to be observed ? The 

 only one of these which can be detected by the finger is the 

 dicrotic wave, and this only when it is well marked. When 

 it can be felt, the pulse is said to be dicrotic, and, as before 

 stated, this indicates an actively acting heart with an arterial 

 pressure low relatively to the strength of the ventricles. 



B. Capillary Pulse. 



Normally there is no pulse in the capillaries. Their thin 

 endothelial wall is not well adapted to bear such an inter- 

 mittent strain. If, however, the arterioles to a district are 

 freely dilated so that little resistance is offered to the escape 



