Question

Figure 12.4 shows simultaneous records of changes in right hand and left forearm volume when collecting pressures are applied intermittently by means of cuffs on the right wrist and left upper arm respectively. The volume of the hand in the plethysmograph was 300 ml and the volume of the forearm was 600 ml. These records (venous occlusion plethysmograms) show:

a. A greater hand blood flow in the third than in the fourth plethysmogram.

b. That the rate of blood flow per unit volume of tissue is similar in the hand and forearm.

c. That hand blood flow is more variable than forearm blood flow.

d. That forearm blood flow is nearer 20 than 50 ml/minute.

e. That the collecting cuffs are not occluding the arteries.

Answer 1

a. False Flow is measured as increase in volume with time and hence is directly proportional to the slope of the volume record during collection.

b. False The total blood flow rates are similar on the two sides; since hand volume is half that of the forearm, its rate of flow per unit volume of tissue is approximately double forearm flow.

c. True The slopes are more variable; the more variable flow is due to greater variability in the level of sympathetic vasoconstrictor tone.

d. False The rate of flow is quite close to 50 ml/minute.

e. True If the arteries were occluded, flow would be zero.