We may now reflect on what can influence vessel stiffness. Westerbacka and Yki-Jarvinen have argued that vessel stiffness is one of the features of insulin resistance, with obese and other insulin resistant subjects showing an increase in the reflected wave, seen as a larger augmentation index in systole. They have also shown that this augmentation index in healthy subjects is reduced within 30 minutes of the administration of insulin, while in obese subjects, who have an increased augmentation index at baseline, the insulin resistance is associated with a much slower and smaller decline of augmentation index. They argue that the effect of insulin on large vessel stiffness is independent of its vasodilatation effect because the time course of insulin-induced vasodilatation is much slower than that of the fall in augmentation. It is proposed, then, that the relationship between insulin resistance and macrovascular disease is that insulin resistant subjects have stiffer blood vessels with an increased pulse pressure.