BLOOD VESSELS 443 



them further only slightly. On the other hand, if the diastolic 

 pressure is low, the arterial wall is lax, and is readily stretched 

 to a greater extent. 2nd. The force of the heart which de- 

 termines the systolic pressure. To stretch the arterial wall to 

 a large extent requires an actively contracting heart throwing 

 a large wave of blood into the arterial system at each systole. 

 The full pulse is well seen after violent exertion, when the 

 heart is active and the peripheral vessels moderately dilated. 

 It is also seen in a slow pulse, on account of the greater 

 diastolic filling of the ventricles. 



4!th. Tension of the pulse. This is really a measure of 

 the maximum systolic blood pressure, which may be more 

 accurately measured by the Riva Rocci apparatus (p. 448). 

 To test it, two fingers must be placed upon the artery, and 

 the one nearer the heart pressed more and more firmly on 

 the vessel until the pulse wave is no longer felt under the 

 other finger. 



The tension of the pulse varies directly with the force of 

 the heart and with the peripheral resistance. The first state- 

 ment 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 hiofh-tension 

 pulse is indicative of a strongly acting heart with constric- 

 tion 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. 



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

 means of the finger alone, or by means of the sphygmo- 

 graph. The points to be observed are : — 



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

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

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

 former condition is indicative of an actively contracting heart 

 with no great peripheral resistance — the latter indicates that 

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

 blood pressure. 



