Patent ID: 7139599

Claim:
A method of processing at least first and second plethysmographic signals obtained from a patient, the first and second plethysmographic signals being obtained in a first domain, said method comprising the steps of: transforming the first and second plethysmographic signals from the first domain to a second domain different from the first domain to obtain first and second plethysmographic signals in the second domain; applying log transformations to the first and second plethysmographic signals in the second domain to obtain first and second log transformed plethysmographic signals in the second domain; transforming the first and second log transformed plethysmographic signals in the second domain to a third domain different from the first and second domains to obtain first and second plethysmographic signals in the third domain; examining at least the first and second plethysmographic signals in the third domain to obtain information therefrom relating to a physiological condition of the patient, wherein said step of examining at least the first and second plethysmographic signals in the third domain comprises identifying a peak in the first plethysmographic signal in the third domain associated with a pulse rate of the patient and identifying a peak in the second plethysmographic signal in the third domain associated with a pulse rate of the patient; determining a DC level of the first plethysmographic signal in the second domain; determining a DC level of the second plethysmographic signal in the second domain; obtaining an AC level of the first plethysmographic signal in the first domain from the identified peak in the first plethysmographic signal in the third domain; obtaining an AC level of the second plethysmographic signal in the first domain from the identified peak in the second plethysmographic signal in the third domain; and computing a value correlated with a blood analyte level of the patient from the DC levels of the first and second plethysmographic signals in the second domain and the AC levels of the first and second plethysmographic signals in the first domain.