A method and an apparatus for distinguishing concentrations of blood constituents among distinct vascular components in situ. The method has steps of inducing periodic vibration, characterized by a frequency, in a limb of a person in such as manner as to selectively excite a resonant response in a specified...http://www.google.com/patents/US6947781?utm_source=gb-gplus-sharePatent US6947781 - Vibratory venous and arterial oximetry sensor
