Controlling flow of exhaled breath during analysis
The flow rate of a gaseous sample of exhaled breath through an analytical device is controlled by a pump, and in certain embodiments two pumps. Placement of the analyte sensor in a secondary stream branching off of the primary stream through the device offers further control over the manner, duration, and quantity of the breath that is placed in contact with the sensor.
1. A diagnostic apparatus for detecting an analyte in exhaled breath, said apparatus comprising:
a housing having a flow-through passage and adapted to receive exhaled breath from a subject;
an analyte sensing element responsive to said analyte when retained in said flow-through passage; and
a pump means for moving said exhaled breath from a subject and through said flow-through passage at a controlled rate;
wherein said flow-through passage comprises a primary passage and a secondary passage branched off from said primary passage;
wherein said flow-through passage divides into said primary passage and said secondary passage at an upstream junction in said flow-through passage and said secondary passage recombines with said primary passage at a downstream junction in said flow-through passage; and
wherein said pump means comprises a first pump in said primary passage and a second pump in said secondary passage.
2. The apparatus of claim 1 further comprising a pressure sensor arranged to detect the pressure of exhaled breath entering said primary flow-through passage.
3. The apparatus of claim 1 further comprising flow resistance means in said primary flow-through passage.
4. The apparatus of claim 3 wherein said flow resistance means is an orifice.
5. The apparatus of claim 3 wherein said flow resistance means is a variable flow resistor.
6. The apparatus of claim 1 wherein said primary and secondary flow-through passages are vented separately.
7. The apparatus of claim 1 further comprising a valve arranged to allow or prevent flow through said secondary flow-through passage.
8. The apparatus of claim 1 further comprising a check valve in said secondary flow-through passage.
9. The apparatus of claim 1 further comprising a first flow resistance means in said primary flow-through passage and a second flow resistance means in said secondary flow-through passage.
10. The apparatus of claim 9 wherein said first flow resistance means is a variable flow resistor.
11. The apparatus of claim 1 wherein said analyte sensing element is cytochrome c in a sol-gel matrix.
12. The apparatus of claim 1 wherein a concentration of the analyte to which the analyte sensing element is responsive is less than 1 part per million.
13. The apparatus of claim 1 wherein a concentration of the analyte to which the analyte sensing element is responsive is less than 100 parts per billion.
14. The apparatus of claim 1 wherein the analyte is nitric oxide (NO).
15. The diagnostic apparatus of claim 1 , wherein the exhaled breath moved through the primary and secondary through passages is released to a surrounding atmosphere downstream of the recombination of the primary and secondary passages.