US-12622600-B2 - System and method for mainstream exhaled oxygen sensor

Abstract

According to various embodiments, a sensing device for measuring oxygen concentration cycles in breath is disclosed. The sensing device includes a laser configured to emit light at an A-band of oxygen, a lens configured to collimate the light, and a multi-pass cell configured to contain a replaceable sample cell. The light passes through the multi-pass cell and is attenuated by oxygen in the sample cell. The sensing device further includes a photodetector configurated to convert the attenuated light into an electrical signal, and a lock-in amplifier or an equivalent processing circuit configured to determine oxygen concentration from the electrical signal.

Inventors

• Charles L. Patrick
• Jonas WESTBERG
• Gerard Wysocki

Assignees

• THE TRUSTEES OF PRINCETON UNIVERSITY

Dates

Publication Date

20260512

Application Date

20200506

Claims (10)

1. 1 . A sensing device for measuring oxygen concentration cycles in breath, comprising: a laser configured to emit light at an A-band of oxygen; a lens configured to collimate the light; a multi-pass cell configured to contain a replaceable sample cell, wherein the light passes through the multi-pass cell and is attenuated by oxygen in the replaceable sample cell, the replaceable sample cell comprising a first window between the lens and multi-pass cell and a second window between the multi-pass cell and photodetector; a photodetector configured to convert the attenuated light into an electrical signal; and a lock-in amplifier configured to determine oxygen concentration from a ratio of 1st and 2nd harmonic signal values of the electrical signal, where the lock-in amplifier is further configured to determine a 3rd harmonic signal value that determines a center of oxygen transition for locking a frequency of the laser to the center of the oxygen transition.
2. 2 . The sensing device of claim 1 , wherein the laser comprises a semiconductor laser.
3. 3 . The sensing device of claim 1 , wherein the laser is further configured to emit a single frequency radiation coinciding with the A-band of oxygen.
4. 4 . The sensing device of claim 1 , wherein the first and a second windows are one of anti-reflection coated windows and Brewster angled windows.
5. 5 . The sensing device of claim 1 , wherein the multi-pass cell comprises a concave mirror at each end configured to fold a path of the light multiple times.
6. 6 . The sensing device of claim 1 , wherein the laser is further configured to operate in a continuous wave mode at about 760-765 nm.
7. 7 . The sensing device of claim 1 , wherein the lock-in amplifier is further configured for wavelength modulation spectroscopy.
8. 8 . The sensing device of claim 1 , wherein the lock-in amplifier is further configured to determine the 1st and 2nd harmonic signal values that determine oxygen concentration from a ratio of the 1st and 2nd harmonic signal values using 2f/f normalization.
9. 9 . The sensing device of claim 1 , wherein oxygen is measured at a rate of 100 Hz.
10. 10 . The sensing device of claim 1 , wherein the sample cell is integrated in a replaceable airway adapter to be inserted into the sensing device.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to provisional application 62/844,306, filed May 7, 2019, which is herein incorporated by reference in its entirety. FIELD OF THE INVENTION The present invention relates generally to measuring oxygen and, more particularly, to a system and method to measure oxygen concentration cycles in breath for health monitoring. BACKGROUND OF THE INVENTION Monitoring of the rate of oxygen consumption in critical care patients provides unique insight into metabolic function and may therefore be of use in a variety of clinical settings. However, time-resolved and accurate sampling of the human breath cycle with a desired accuracy of <1% of O2 and a sampling rate of 100 Hz places high demands on the oxygen sensor. So far, commercially available techniques for oxygen monitoring in breath are either bulky, limited in accuracy, or have slow response times. Many of these issues can be effectively addressed by the recent advances of laser spectroscopy, whose strengths are high temporal resolution, selectiveness, and sensitivity, all provided in a non-invasive manner. However, the small absorption cross-sections of O2 is often compensated with long absorption pathlengths or other optical enhancement techniques to reach the desired minimum detection limits (MDL), which often lead to bulky sensors with large sampling volumes undesired for routine mainstream breath monitoring. The ideal form factor for the oxygen sensor is similar to conventional capnography instruments that are routinely used for monitoring breath via airflow rate and CO2 concentration measurements. Providing an oxygen sensing platform as a complement to the established CO2 sensors will further expand the routine breath analysis applications by enabling collection of additional metabolic function data. Hospital rooms are fitted with many vital sign monitors: heart rate, blood pressure, body temperature, etc. However, the rate of oxygen consumption while breathing is not measured routinely. Monitoring of the rate of oxygen consumption of patients in critical care provides insight into the metabolic function of the patients which is useful in several clinical dilemmas: neo-natal complications, sepsis identification, hypoxia detection, and nonresponsive patient monitoring. Real time breath measurement must be accurate and precise in order to clearly resolve the cycles within each breath that are indicative of various ailments. Devices used in medical settings must also be user friendly, robust, and compact. Devices must also utilize a sterilized replaceable adapter. As such, there is a need for an oxygen sensor based on laser spectroscopy that addresses the above requirements. SUMMARY OF THE INVENTION According to various embodiments, a sensing device for measuring oxygen concentration cycles in breath is disclosed. The sensing device includes a laser configured to emit light at an A-band of oxygen, a lens configured to collimate the light, and a multi-pass cell configured to contain a replaceable sample cell. The light passes through the multi-pass cell and is attenuated by oxygen in the sample cell. The sensing device further includes a photodetector configurated to convert the attenuated light into an electrical signal, and a lock-in amplifier configured to determine oxygen concentration from the electrical signal. According to various embodiments, a sensing device for measuring oxygen concentration cycles in breath is disclosed. The sensing device includes a laser configured to emit light at an A-band of oxygen, a lens configured to collimate the light, and a multi-pass cell configured to contain a replaceable sample cell. The light passes through the multi-pass cell and is attenuated by oxygen in the sample cell. The sample cell includes a first window between the lens and multi-pass cell and a second window between the multi-pass cell and photodetector. The sensing device further includes a photodetector configurated to convert the attenuated light into an electrical signal, and a lock-in amplifier configured to determine oxygen concentration from the electrical signal. According to various embodiments, a sensing device for measuring oxygen concentration cycles in breath is disclosed. The sensing device includes a laser configured to emit light at an A-band of oxygen, a lens configured to collimate the light, and a multi-pass cell configured to contain a replaceable sample cell. The light passes through the multi-pass cell and is attenuated by oxygen in the sample cell. The sensing device further includes a photodetector configurated to convert the attenuated light into an electrical signal, and a processing circuit configured to determine oxygen concentration from the electrical signal. Various other features and advantages will be made apparent from the following detailed description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS In order for the advantages of the invention to be r