Method and apparatus for analyzing pulmonary performance

1. A method for performing a pulmonary test, comprising:

while a patient inspires through a testing device such that the patient causes a stream of gas to flow from an open end of the testing device and through the testing device, injecting a test gas into the stream of gas via an injector directed towards the open end of the testing device, the injection of the test gas controlled by a processor, wherein, for a time interval, a volume of the test gas injected into the stream of gas is greater than a volume of gas inspired by the patient, and wherein the time interval comprises a plurality of successive sampling time intervals;

measuring, using a gas flow sensor, a flow rate of the inspired gas, the inspired gas including at least a portion of the test gas;

measuring a concentration of the test gas in the inspired gas; and

injecting, for each sampling time interval from the plurality of successive sampling time intervals, a volumetric flow rate of the test gas that is greater than a volumetric flow rate of gas inspired by the patient.

2. The method of claim 1 , wherein the injector is directed away from a patient mouthpiece of the testing device.

3. The method of claim 1 , further comprising:

changing a composition of the test gas while a mouthpiece of the testing device is in the patient's mouth.

4. The method of claim 1 , further comprising:

changing the volumetric flow rate of the test gas for each sampling time interval from the plurality of successive sampling time intervals.

5. The method of claim 1 , further comprising:

determining an inspired volume of the test gas using the following equation:

V

X

=

∑

[

ⅆ

V

1

ⅆ

t

⁢

F

X

]

i

⁢

Δ

⁢

⁢

T

i

where V X is a total volume of the test gas inspired by the patient,

ⅆ

V

1

ⅆ

t

is a volumetric flow rate of the inspired gas over a sample interval, F X is a fraction of the test gas in the inspired gas during the sample interval, ΔT i is the sample interval, and i is a reference indicating which member the sample interval represents in a set of sample intervals.

6. The method of claim 5 , wherein the determining the inspired volume of the test gas is performed by the processor.

7. The method of claim 1 , wherein the open end is open to ambient atmosphere while the patient inspires through the testing device.

8. The method of claim 1 , wherein:

the open end is open to ambient atmosphere while the patient inspires through the testing device; and

the testing device includes a mouthpiece opposite the open end.

9. The method of claim 8 , wherein:

the testing device includes a breathing conduit fluidically coupling the open end to the mouthpiece; and

the breathing conduit provides substantially no resistance to inspiration.

10. The method of claim 1 , wherein:

the open end is open to ambient atmosphere while the patient inspires through the testing device;

the testing device includes a mouthpiece opposite the open end;

the testing device includes a breathing conduit fluidically coupling the open end to the mouthpiece; and

a volumetric flow rate at which the test gas is injected is greater than a volumetric flow rate of gas flowing through the mouthpiece, such that the test gas prevents or inhibits ambient atmosphere from being inspired.

11. The method of claim 10 , wherein the volumetric flow rate at which the test gas is injected causes a uniform distribution of test gas across the breathing conduit that provides a wall of the test gas that prevents or inhibits the ambient atmosphere from being inspired.

12. The method of claim 1 , wherein:

the open end is open to ambient atmosphere while the patient inspires through the testing device;

the testing device includes a mouthpiece opposite the open end;

the testing device includes a breathing conduit fluidically coupling the open end to the mouthpiece such that while the patient inspires, the stream of gas flows in a first direction from the open end, through the breathing conduit, and to the mouthpiece, the breathing conduit defining a centerline of the testing device; and

the injector is directed such that the test gas is injected along an injection direction that has an angle that is less than 90 degrees relative to the centerline.

13. The method of claim 1 , wherein:

the open end is open to ambient atmosphere while the patient inspires through the testing device;

the testing device includes a mouthpiece opposite the open end; and

the testing device includes a breathing conduit fluidically coupling the open end to the mouthpiece, the breathing conduit defining a centerline of the testing device, the injector disposed at an angle that is less than 90 degrees relative to the centerline.

14. A method, comprising:

placing a mouthpiece of a testing device to a patient's mouth, the testing device having a first end portion containing the mouthpiece, a second end portion opposite the first end portion and containing an end open to ambient air, and a breathing conduit disposed between the first end portion and the second end portion;

measuring a volumetric flow rate of inspired gas flowing through the breathing conduit when the patient inspires, the inspired gas flowing from the end open to ambient air towards the mouthpiece; and

injecting a test gas into the inspired gas at the second end portion of the testing device while the inspired gas flows through the second end portion, the test gas injected via an injector directed towards the end open to ambient air, the injection of the test gas controlled by a processor, wherein the test gas is injected into the second end portion with a volumetric flow rate greater than the volumetric flow rate of the inspired gas such that the test gas prevents or inhibits ambient air from entering the breathing conduit when the patient inspires.

15. The method of claim 14 , further comprising measuring a concentration of the test gas in the breathing conduit.

16. The method of claim 14 , further comprising measuring a concentration of the test gas when the patient expires.

17. The method of claim 14 , wherein a volumetric flow rate at which the test gas is injected causes a uniform distribution of test gas across the breathing conduit that provides a wall of the test gas that prevents or inhibits the ambient atmosphere from being inspired.

18. The method of claim 14 , wherein the breathing conduit provides substantially no resistance to inspiration.