Methods and systems for extracting venous pulsation and respiratory information from photoplethysmographs

A method for extracting a respiratory signal and a blood oxygen level from a red photoplethysmographic signal and an infrared photoplethysmographic signal comprising the steps of:

• receiving the red photoplethysmographic signal and the infrared photoplethysmographic signal;
• filtering the red photoplethysmographic signal and the infrared photoplethysmographic signal;
• separating the red photoplethysmographic signal into a first signal component and a second signal component;
• separating the infrared photoplethysmographic signal into a third signal component and a fourth signal component;
• determining a red venous signal from the first signal component and a red arterial signal from the second signal component;
• determining an infrared venous signal from the third signal component and an infrared arterial signal component from the fourth signal component;
• extracting the red arterial signal and the red venous signal from the red photoplethysmographic signal;
• extracting the infrared arterial signal and the infrared venous signal from the infrared photoplethysmographic signal;
• extracting the respiratory signal using the red photoplethysmographic signal and the red venous signal;
• and,
• extracting the blood oxygen signal using the red arterial signal and the infrared arterial signal;
• wherein the step of extracting the respiratory signal further comprises the steps of:
• determining a red signal derivative of the red photoplethysmographic signal;
• determining a red venous signal derivative of the red venous signal;
• generating a time domain window signal from the red signal derivative and the red venous signal derivative;
• generating a windowed signal from the time domain signal and the red venous signal derivative;
• determining a maximum amplitude from the windowed signal;
• determining a venous return variation from the maximum amplitude;
• interpolating the venous return variation;
• and,
• filtering the venous return variation to generate the respiratory signal.

A system for extracting arterial, venous, blood oxygen, and respiratory information from a set of photoplethysmographic signals comprising:

• an extractor;
• a set of photoplethysmographic sensors outputting a set of photoplethysmographic signals, each photoplethysmographic sensor connected to the extractor;
• a computing device connected to the extractor and programmed to:
• preprocess the set of photoplethysmographic signals;
• locate a venous signal and an arterial signal in each photoplethysmographic signal of the set of photoplethysmographic signals using second order blind identification;
• extract the arterial signal and the venous signal from each photoplethysmographic signal of the set of photoplethysmographic signals;
• extract a respiratory signal using the venous signal and the arterial signal;
• and,
• extract a blood oxygen saturation from the arterial signal;
• wherein each photoplethysmographic sensor comprises a red LED and an infrared LED;
• wherein the set of photoplethysmographic signals comprises a red signal and an infrared signal;
• wherein the red signal further comprises a red venous signal and a red arterial signal;
• and,
• wherein the computing device is further programmed to:
• receive the red signal from the red LED;
• receive the infrared signal from the infrared LED;
• determine a red signal derivative of the red signal;
• determine a red venous signal derivative for the red venous signal;
• generate a time domain window signal from the red signal derivative and the red venous signal derivative;
• generate a windowed signal from the time domain signal and the red venous signal derivative;
• determine a maximum amplitude from the windowed signal;
• determine a venous return variation from the maximum amplitude;
• interpolate the venous return variation;
• and,
• filter the venous return variation to generate the respiratory signal.