Additional history would be helpful such as health conditions and medications he is taking. If he is a smoker ask him to stop. There are medications for peripheral circulation but they are of limited effectiveness. Depending upon the origin of the problem surgery is sometimes curative. It should be emphasized however that an exercise program for this purpose leads to a significant improvement in function independent of any actual change in circulation. Finally - I assume that he has undergone testing and that this is not simply an impression but rather a diagnosis.