MEASUREMENT OF MASS MOVEMENT OF BLOOD 285 



cause great changes in the character of the pulse beat, does not decid- 

 edly affect the mass movement of the blood. In aneurism of the sub- 

 clavian artery, the bloodflow may be much greater in the corresponding 

 than in the opposite hand, even though the amplitude of the pulse is 

 very obviously diminished and the difference between the systolic and 

 diastolic pressures (the pressure pulse) is much less on the affected 

 than on the normal side. By ordinary clinical measurements, there- 

 fore, false estimates of bloodflow are quite likely to be made. These 

 results are no doubt owing partly to vasodilatation brought about by 

 pressure of the aneurism on the brachial plexus and partly to the 

 lower resistance to the flow of blood into the dilated subclavian. 



In Raynaud's disease, as would be expected, the flow is small, the 

 diminution being more or less proportional to the duration of the 

 disease. The contralateral vasomotor reaction to cold is also pecu- 

 liarly intense. 



In diabetic gangrene of the feet there is a very subnormal flow in both 

 the hands and the feet. The vasomotor reflexes are also feeble. 



It is sometimes difficult to tell whether an observed curtailment of 

 flow is a nervous (reflex) effect or is due to some mechanical interfer- 

 ence. There are two ways by which the exact cause may be diagnosed: 

 (1) by observing the flow from day to day; if it remains unchanged, 

 any alteration must be dependent on mechanical causes ; (2) by observ- 

 ing the change in flow brought about by altering the temperature of the 

 room or calorimeter and seeing whether the ratio between the two hands 

 remains unchanged or becomes altered. If the latter occurs, the in- 

 equality in flow must be due to nervous causes. 



Diseases of the Nervous System. The effect of neuritis on the flow 

 varies with the duration of the disease. In cases of early peripheral 

 unilateral neuritis there may be an increase of flow altering the ratio be- 

 tween the two hands with the greater flow on the diseased side. In 

 neuritis of long standing the flow is cut down, the greater flow occurring 

 on the healthy side. The changes here are probably due to anatomical 

 alterations in the lumen of the tube, perhaps a thickening of the intima. 

 In motor-neuron disease without any involvement of the sensory skin 

 nerves the flow seems to remain normal and the reflexes to be well- 

 marked. This indicates that involvement of the motor nerves does not 

 interfere with bloodflow to anything like the same degree as involvement 

 of the skin nerves. 



Hemiplegia. A deficiency of bloodflow of the paralyzed side is usually 

 observed, and the vasomotor reflexes are altered, the most usual change 

 being that vasoconstriction is more easily produced than vasodilatation. 



