FIGURE 7.

Theoretical pressure/volume relation in a vein and an artery to explain phenomena observed. At low pressure, veins (blue) have high volume and accommodate more or less blood with little change in transmural pressure. Arteries (red) are round and always distended, and at higher pressure. Change in volume of an artery at low mean pressure is much larger than change in volume at a higher mean pressure. The artery shows greater volume pulsation at a given change of pressure across its wall than at a higher mean pressure.