A TEXTBOOK OF PHYSIOLOGY 



down the pulse just overtopped the arterial pressure. When exposed 

 on a watchglass, as in B, the lumen became deformed and the pulse 

 damped at a much lower pressure. 



If the armlet be placed upon the arm, and kept at a pressure a 

 little below that of the arterial supply to the arm, the limb gradually 

 becomes congested and the superficial veins engorged with blood. 

 Measurement of the pressure in these superficial veins reveals a pressure 

 approximately equal to that registered by the manometer measuring 

 the arterial pressure. The capillaries of the arm, under these condi- 

 tions, become more and more congested; those that were previously 

 mpty gradually fill. An aching feeling comes on, which terminates 

 the experiment. The experiment shows how many capillaries arc 

 empty under normal conditions. In active life we are continually 

 moving our position, so as to prevent continuous pressure on any 

 part and further the circulation. 



Circumstances affecting the Arterial Pressure. The arterial pres- 

 sure is raised during exertion by the more forcible beat of the heart 

 e.g., pressures of 140 to 190 mm. Hg have been observed immediately 

 after running upstairs. It rapidly sinks to a lower level than usual 

 after the exertion is over e.g., 90 mm. Hg owing to the quieter 

 action of the heart and the persistence of the cutaneous dilatation 

 of the bloodvessels which is evoked by the rise of body temperature. 

 In athletes, after a long race, rectal temperatures of 102 to 105 F. 

 have been observed. Mental occupation and excitement raises the 

 arterial pressure. People engaged in brain work have in general a 

 higher pressure than people engaged in purely manual labour working 

 in the same atmospheric conditions. After meals there is a rise in 

 pressure. 



The ordinary statement that inspiration raises and expiration 

 lowers the blood-pressure is only true for an animal under experi- 

 mental conditions. The effect of respiration on the blood-pressure 

 is very complex. A deep intercostal breath, if not too prolonged, 

 yields a fall, a deep diaphragmatic inspiration, a rise, of pressure. 

 Forced breathing causss a fall, while Valsalva's experiment, a deep 

 expiration with the mouth and nose shut, causes a marked rise in the 

 arterial pressure. The effects on the pressure of different types of 

 breathing in a trained subject were as follows: 



Records of the pulse obtained by the suspension method (p. 211) 

 show these results (Fig. 98). In such records a rise in the tracing 

 indicates a rise of pressure, a fall in the tracing, a fall of pressure. 



Increase in the amount of fluid by transfusion cannot raise the 



