Physiological parameter tracking system

1. A physiological parameter tracking system comprising:

a physiological signal input having at least first and second intensity signal components received from a light-sensitive detector that detects light of at least first and second wavelengths transmitted through body tissue carrying pulsing blood, wherein the first and second intensity signal components are at least partially based on a pulse of the pulsing blood;

a reference parameter calculator configured to output a reference parameter responsive to said physiological signal;

a slow parameter calculator configured to output a slow parameter responsive to said physiological signal according to an update command; and

a tracking function calculator configured to output a physiological measurement output responsive to said reference parameter and said slow parameter.

2. The physiological parameter tracking system according to claim 1 further comprising an ancillary parameter calculator configured to output an ancillary parameter responsive to said physiological signal, wherein said slow parameter calculator is configured to output said slow parameter, said slow parameter being responsive to said reference parameter and said ancillary parameter.

3. The physiological parameter tracking system according to claim 2 further comprising an output multiplexer configured to output said physiological measurement as being responsive to one of a tracking function output and said ancillary parameter according to said update command.

4. The physiological parameter tracking system according to claim 2 wherein said ancillary parameter comprises a measure of venous oxygen saturation, said reference parameter comprises a measure of arterial oxygen saturation, said slow parameter comprises a measure of oxygen consumption and said physiological measurement output is indicative of venous oxygen saturation.

5. The physiological parameter tracking system according to claim 1 wherein said slow parameter comprises a measure of abnormal hemoglobin, said reference parameter comprises a measure of oxygen saturation and said physiological measurement is indicative of oxygen saturation corrected for abnormal hemoglobin.

6. The physiological parameter tracking system according to claim 1 wherein said update command operates in at least one of a sample and hold mode and a track and hold mode.

7. The physiological parameter tracking system according to claim 1 wherein said physiological measurement output is responsive to a difference between said reference parameter and said slow parameter.

8. A physiological parameter tracking method comprising the steps of:

inputting a physiological signal;

calculating a reference parameter from said signal;

defining an update command;

tracking said reference parameter according to said update command; and

outputting a physiological measurement responsive to said tracking step,

wherein said defining step comprises the substeps of:

indicating one of a sample period and a tracking period for calculating a slow parameter response to said signal; and

indicating a hold period for maintaining a previous calculation of said slow parameter.

9. The physiological parameter tracking method according to claim 8 wherein said tracking step comprises the substep of deriving a tracking function output from said reference parameter and said slow parameter.

10. The physiological parameter tracking method according to claim 9 further comprising the step of calculating an ancillary parameter from said signal.

11. The physiological parameter tracking method according to claim 10 wherein said outputting step comprises the substep of multiplexing said tracking function output and said ancillary parameter according to said update command.

12. The physiological parameter tracking method according to claim 11 wherein said ancillary parameter is venous oxygen saturation and said physiological measurement is said venous oxygen saturation during said tracking period and an estimate of venous oxygen saturation during said hold period.

13. The physiological parameter tracking method according to claim 10 wherein said ancillary parameter is a measure of abnormal hemoglobin.

14. The physiological parameter tracking method according to claim 13 wherein said physiological measurement is arterial oxygen saturation corrected for said abnormal hemoglobin.

15. A physiological parameter tracking method comprising the steps of:

providing a physiological signal;

calculating arterial oxygen saturation from said signal;

calculating a slowly varying parameter during a first period;

holding said slowly varying parameter during a second period; and

outputting a physiological measurement responsive to said arterial oxygen saturation and said slowly varying parameter.

16. The physiological parameter tracking method according to claim 15 wherein said slowly varying parameter is abnormal hemoglobin concentration and said physiological measurement is said arterial oxygen saturation corrected for said abnormal hemoglobin concentration.

17. The physiological parameter tracking method according to claim 15 wherein said slowly varying parameter is a difference between said arterial oxygen saturation and venous oxygen saturation and said physiological measurement is said venous oxygen saturation during said first period and a venous oxygen saturation estimate during said second period.

18. The physiological parameter tracking method according to claim 15 wherein said calculating a slowly varying parameter step comprises the substeps of:

indicating favorable conditions with an update command; and

sampling said slowly varying parameter in response to said command.

19. The physiological parameter tracking method according to claim 15 wherein said holding step comprises the substeps of:

indicating unfavorable conditions with an update command; and

holding said slowly varying parameter in response to said command.