Controlling flow of exhaled breath during analysis

1. A method for determining the amount of an analyte in exhaled breath from a subject, said method comprising

moving exhaled breath from said subject through a flow-through passage in a flow-through device at a constant flow rate by use of at least one pump integrated with said flow-through device, said flow-through device comprising a sensing element responsive to said analyte, wherein said flow-through passage divides into a primary passage and a secondary passage with said sensing element located in said secondary passage, and

dividing the exhaled breath thus moved into said flow-through device at an upstream junction into a primary stream through said primary passage and a secondary stream through said secondary passage so that said exhaled breath is moved from said subject by use of said at least one pump creating parallel simultaneous breath flows through both the primary and the secondary passages,

determining with said sensing element the amount of analyte in the exhaled breath passing through the secondary passage, and

recombining the secondary passage with the primary passage at a downstream junction in said flow-through passage.

2. The method of claim 1 further comprising detecting the pressure of exhaled breath thus moved into said flow-through device.

3. The method of claim 1 , wherein at least one pump comprises a single pump for moving said exhaled breath through said primary passage and said secondary passage.

4. The method of claim 1 , wherein said at least one pump comprises a first pump comprises a first pump in said primary passage and a second pump in said secondary passage.

5. The method of claim 1 wherein said flow-through device comprises a valve in said secondary passage, and said method further comprises retaining a sample of said exhaled breath in contact with said sensing element in said secondary passage for a selected period of time by closing said valve and stopping the flow through said secondary passage after expiration of a fixed period of time of simultaneous parallel flows through both the primary and secondary passages.

6. The method of claim 5 further comprising opening said valve to allow flow through said secondary passage at an interval of between 5 seconds and 9 seconds after the start of flow of exhaled breath through said device in order to create the simultaneous parallel flows through both the primary and secondary passages.

7. The method of claim 6 wherein said interval is between 6 seconds and 8 seconds.

8. The method of claim 6 further comprising maintaining said flow through said secondary passage for a duration of between 1 second and 10 seconds.

9. The method of claim 8 wherein said duration is between 1 and 7 seconds.

10. The method of claim 8 wherein said duration is between 1 and 5 seconds.

11. The method of claim 5 , wherein said method further comprises varying the flow rate of said at least one pump so that the sum of the flow rate through the primary passage and the secondary passage when the valve is open will equal the flow rate through the primary passage when the valve is closed, thus maintaining a constant flow rate through the flow through passage.

12. The method of claim 1 comprising drawing said exhaled breath through said secondary passage at a flow rate of 5 cm 3 /s to 11 cm 3 /s.

13. The method of claim 1 comprising drawing said exhaled breath through said secondary passage at a flow rate of 6 cm 3 /s to 10 cm 3 /s.

14. The method of claim 1 comprising drawing said exhaled breath through said secondary passage at a flow rate of 7 cm 3 /s to 9 cm 3 /s.

15. The method of claim 1 comprising drawing said exhaled breath through said primary passage at a flow rate of 40 cm 3 /s to 45 cm 3 /s.