Patent ID: 7674231

Claim:
A method for deriving an output circulatory metric at an extremity of a subject, the method comprising: measuring a first plethysmographic signal at a first position on the extremity of the subject and measuring a second plethysmographic signal at a second position on the extremity of the subject, each of the signals being measured at a plurality of heights, by means of a sensor disposed on the extremity of the subject, the second position characterized by a distance between the first position and the second position; establishing a functional relationship using a digital computer, the functional relationship based at least on the measurements of the first and second plethysmographic signals at the plurality of heights, the functional relationship providing a quantitative relationship between the first and second plethysmographic signals and the output circulatory metric absent a direct measurement of the output circulatory metric at each of the plurality of heights; and calculating a transit time of a circulatory pressure wave based on the first and second plethysmographic signals; deriving a wave speed based on the calculated transit time and the distance between the first and second positions; and applying the functional relationship to derive the output circulatory metric.