VELOCITY AND PRESSURE OF BLOOD-FLOW, 



493 



pressure. (2) By using a mercury manometer provided with 

 maximum and minimum valves. Of the manometers that have 

 been devised to register the quick changes in pressure exhibited 

 in the cavity of the heart itself, or in the pulsations of the arteries 

 due to the heart-beat, the ones that have given the most accurate 

 results are the membrane-manometer of Hiirthle and the optical 

 manometers which depend upon the use of the segment-capsule 

 devised by Frank. 



The principle made use of in the Hiirthle manometer is illustrated 

 by the diagram in Fig. 196. The instrument consists essentially of a small 

 box or tambour of very limited capacity; the top of the tambour is covered 

 with thin rubber dam and the cavity is filled with liquid and connected by 

 rigid tubing, also filled with liquid, with the interior of the artery or heart. 

 Variations in pressure in the artery are transmitted tlirough the column of 

 liquid to the rubber membrane of the tambour, and the movements of this 

 latter are greatly magnified by a sensitive lever attached to it. The liquid 

 conduction and the small size of the tambour, which prevents any notice- 

 able outflow of liquid, combine to make a sensitive and very prompt recorder 

 of pressure changes. It is necessary to calibrate this instrument whenever 

 used in order to give absolute values to the records obtained. A specimen 



Fig. 198. — Blood-pressure record from a dog with a Hiirthle manometer. The size 

 f.f the heart beats is relatively much greater than with a mercury manometer. In this case 

 the systolic pressure is about 150 mms. Hg; the diastolic, 100 mms. ; and the heart beat ot 

 pulse pressure, 50 mms 



F/sfe 



A B 



Fig. 198o. — ^A, The segment capsule. One side of a recording tambour is flattened so that 

 a segment is cut off. Thin rubber-dam is stretched over the capsule. A small trapezoidal piece 

 of thin celluloid (c) is cemented to the rubber, so that its broad side pivots on the chord side 

 of the circle. On this, in turn, is cemented a small mirror (m), so that its diameter also pivots 

 on the chord side of the circle. 



B, Diagram to show the band of light reflected from the mirror of the segment capsule to 

 a photographic plate. In this way a photographic record is obtained of the movements of the 

 mirror caused by the pressure changes transmitted to the segment-capsule.— (From Wiggers.) 



of a blood-pressure record obtained with this instrument is shown in Fig. 198. 

 It will be noticed that the size of the heart- beat, relative to the distance from 



