Venous oxygen saturation systems and methods

摘要

Methods and systems are discussed for determining venous oxygen saturation by calculating a ratio of ratios from respiration-induced baseline modulations. A calculated venous ratio of ratios may be compared with a look-up table value to estimate venous oxygen saturation. A calculated venous ratio of ratios is compared with an arterial ratio of ratios to determine whether baseline modulations are the result of a subject's respiration or movement. Such a determination is also made by deriving a venous ratio of ratios using a transform technique, such as a continuous wavelet transform. Derived venous and arterial saturation values are used to non-invasively determine a cardiac output of the subject.

主权项

1. A method for determining a respiration rate of a subject, the method comprising:
transforming, using a signal processor, a first physiological signal based on light transmission at a first wavelength to generate a first transformed signal; transforming, using the signal processor, a second physiological signal based on light transmission at a second wavelength to generate a second transformed signal; deriving, using the signal processor, a ratio surface from the first transformed signal and the second transformed signal, wherein the ratio surface comprises three-dimensional data with dimensions including time and scale; identifying, using the signal processor, a first region of interest on the ratio surface indicative of venous perturbation; calculating, using the signal processor, a representative value for the first region of interest on the ratio surface; making, using the signal processor, a determination as to whether the calculated representative value for the first region of interest indicates respiration or motion of the subject based on the calculated representative value, wherein determining whether the representative value for the first region of interest indicates respiration or motion of the subject comprises:
calculating a representative value for a second region of interest of the ratio surface related to a cardiac pulse frequency;calculating a short-term difference between the representative value for the second region of interest and the representative value for the first region of interest; andcomparing the short-term difference with a long-term difference between historical ratio surface values near the cardiac pulse frequency and an expected respiration frequency, wherein smaller deviations of the short-term difference from the long-term difference are indicative of baseline modulations in the first and second signals being due to respiration, and larger deviations of the short-term difference from the long-term difference are indicative of baseline modulations being due to motion; and calculating, using the signal processor, the respiration rate of the subject when the calculated representative value for the first region of interest indicates respiration.