Systems and methods of extracting information relating to diameter and/or diameter changes in small blood vessels such as arterioles. This information may be used to assess a degree of vasoconstriction and/or vasodilatation. In one method, changes in vessel cross-section due to pulse wave arrival is assessed in both arterioles and in larger arteries. A time delay between the changes and/or a change in time delay is optionally associated with arteriole cross-section and/or changes therein.
