Passive, proportional measurement of oxygen and carbon dioxide consumption for assessment of metabolic parameters

Patent metadata

Field	Value
Publication number	US-11464426-B2
Application number	US-201916414003-A
Country	US
Kind code	B2
Filing date	May 16, 2019
Priority date	May 16, 2018
Publication date	Oct 11, 2022
Grant date	Oct 11, 2022

Abstract

A conventional flow tube for a metabolic cart is usually a straight length of pipe whose inner diameter is fixed by the respiratory burden imposed by the flow tube on the user, with a smaller diameter imposing a higher respiratory burden. The ratio of the straight flow tube's length to diameter is fixed by fluid dynamics, so increasing the flow tube's diameter causes the flow tube's length to increase. As the flow tube gets longer, it exerts more torque on the user's neck and jaw, creating discomfort. Reducing the flow tube's length causes an undesired increase in the respiratory burden but increasing the flow tube's diameter to reduce the respiratory burden makes the flow tube less comfortable, making the flow tube unconformable, hard to breathe through, or both. Bending the flow tube, e.g., in an L shape, makes it possible to increase the flow tube's propagation length without increasing the flow tube's lever arm length.

First claim

The invention claimed is:

1. A flow-rate proportional passive side-stream sampling system comprising:
a bent flow tube, defining an inner lumen extending from an inlet of the bent flow tube to an outlet of the bent flow tube, the bent flow tube having a bend between the inlet and the outlet, the bent flow tube configured to receive an exhaled breath from a person at the inlet, convey the exhaled breath from the inlet to the outlet via the bent flow tube, and convey an inhalation from the outlet to the inlet and to the person via the bent flow tube;
a first port disposed on the bent flow tube between the inlet of the bent flow tube and the bend and in fluid communication with the inner lumen;
a mixing chamber, in fluid communication with the first port, to receive a fraction of the exhaled breath collected in proportion to an instantaneous flow rate of the exhaled breath via the first port; and
at least one sensor, in fluid communication with gas in the mixing chamber, to measure at least one of a volumetric flow rate, an oxygen content, a carbon dioxide content, an oxygen partial pressure, or a carbon dioxide partial pressure of the fraction of the exhaled breath.

2. The flow-rate proportional passive side-stream sampling system of claim 1 , wherein the bend has a curve of about 75 degrees to about 105 degrees between the inlet and the outlet.

3. The flow-rate proportional passive side-stream sampling system of claim 1 , wherein the bent flow tube has a second port disposed between the outlet of the bent flow tube and the bend, the second port in fluid communication with the mixing chamber and the inner lumen.

4. The flow-rate proportional passive side-stream sampling system of claim 1 , further comprising:
at least one valve, disposed between the inlet and the bend and in fluid communication with the inner lumen, to relieve pressure in the inner lumen during an inhalation by the person.

5. The flow-rate proportional passive side-stream sampling system of claim 1 , further comprising:
a saliva trap, disposed in fluid communication with the inner lumen, to collect saliva excreted by the person.

6. The flow-rate proportional passive side-stream sampling system of claim 1 , further comprising:
a removable mouthpiece connected to the inlet of the bent flow tube.

7. The flow-rate proportional passive side stream sampling system of claim 1 , wherein the mixing chamber further comprises a perforated baffle and/or a perforated circuit board disposed between the inlet and the at least one sensor to foster mixing of multiple breath fractions.

8. The flow-rate proportional passive side stream sampling system of claim 1 , wherein the at least one sensor is disposed in the mixing chamber.

9. The flow-rate proportional passive side-stream sampling system of claim 1 , wherein the bend substantially prevents the inhalation from flowing into the mixing chamber via the first port.

10. A method of proportional passive flow-rate sampling, the method comprising:
receiving an exhaled breath from a person at an inlet of a rigid bent flow tube;
conveying a fraction of the exhaled breath from a first port between the inlet of the rigid bent flow tube and a J-shaped bend in the rigid bent flow tube to a mixing chamber, the fraction of the exhaled breath being in proportion to an instantaneous flow rate of the exhaled breath; and
measuring, with at least one sensor, at least one of a volumetric flow rate, an oxygen content, a carbon dioxide content, an oxygen partial pressure, or a carbon dioxide partial pressure of the fraction of the exhaled breath.

11. The method of claim 10 , wherein the J-shaped bend in the rigid bent flow tube is about 75 degrees to about 105 degrees between the inlet and the outlet, the rigid bent flow tube defining an inner lumen extending from a proximal end of the rigid bent flow tube to a distal end of the rigid bent flow tube to convey the exhaled breath from the proximal end to the distal end.

12. The method of claim 11 , further comprising:
actuating at least one valve, disposed between the inlet and the J-shaped bend in the rigid bent flow tube, to relieve pressure in the inner lumen during an inhalation by the person.

13. The method of claim 10 , wherein the rigid bent flow tube has a second port disposed between the J-shaped bend and an outlet of the rigid bent flow tube, and further comprising:
conveying gas from the mixing chamber to the second port; and
emitting the gas via the outlet.

14. The method of claim 10 , further comprising:
collecting saliva excreted by the person with a saliva trap.

15. The method of claim 10 , further comprising:
mixing fractions of multiple exhaled breaths in the mixing chamber.

16. A flow tube for a metabolic cart, the flow tube comprising:
a proximal end to receive an exhalation from a person;
a distal end;
a bend between the proximal end and the distal end;
a lumen extending from the proximal end to the distal end to convey the exhalation from the proximal end to the distal end;
a first port between the distal end and the bend, fluidically coupled to a mixing chamber and the lumen, to convey a portion of the exhalation from the mixing chamber to the lumen; and
a second port between the single bend and the proximal end, fluidically coupled to the mixing chamber and the lumen, to convey a portion of the exhalation to the mixing chamber from the lumen.

17. The flow tube of claim 16 , wherein the bend is about 75 degrees to about 105 degrees.

18. The flow tube of claim 16 , wherein the bend is about 90 degrees.

19. The flow tube of claim 16 , further comprising:
at least one valve, disposed between the proximal end and the bend and in fluid communication with the lumen, to relieve pressure in the lumen during an inhalation by the person.

20. The flow tube of claim 16 , further comprising:
a saliva trap, disposed in fluid communication with the lumen, to trap saliva excreted by the person.

21. The flow tube of claim 16 , further comprising:
a removable mouthpiece inserted into the proximal end.

22. The flow tube of claim 16 , wherein the flow tube has a length of about 7.75 inches to about 8 inches.

Assignees

• Massachusetts Inst Technology

Inventors

• Mcclung Holly
• Hoyt Reed Wasson
• Candell Lawrence M
• Mahan Joseph M
• Shaw Gary A
• Siegel Andrew M
• Standley Robert Linton
• Thompson Kyle

Classifications

• A61B5/0836

  Measuring rate of CO2 production · CPC title

• A61M16/0808

  Condensation traps · CPC title

• A61B5/082

  Evaluation by breath analysis, e.g. determination of the chemical composition of exhaled breath (A61B5/083, A61B5/091 take precedence) · CPC title

• A61B5/0833

  Measuring rate of oxygen consumption · CPC title

• A61B5/087 Primary

  Measuring breath flow · CPC title