digital plethysmograph: plethysmograph applied to a digit of the hand or foot to measure skin blood flow
plethysmograph: a measuring instrument for measuring changes in volume of a part or organ or whole body (usually resulting from fluctuations in the amount of blood it contains)
phase iv clinical trial: sometimes the FDA approves a drug for general use but requires the manufacturer to continue to monitor its effects; during this phase the drug may be tried on slightly different patient populations than those studied in earlier trials