Nitric oxide measurements in patients using flowfeedback

1. A method performed by a nitric oxide (NO) monitoring system of determining exhaled nitric oxide (FENO) from a patient, the method comprising:

collecting, by a patient breathing circuit, exhaled gases from the patient;

measuring an exhalation flow rate of the exhaled gases as a function of time;

determining an average exhalation flow rate of the exhaled gases based on the measured exhalation flow rate as a function of time;

calculating a baseline correction factor that is a function of the measured FeNO concentration at the average exhalation flow rate and an FeNO concentration for a healthy person at the average exhalation flow rate;

normalizing the measured FeNO concentration using the baseline correction factor to obtain a normalized FeNO;

adjusting the normalized FeNO to a selected flow rate; and

scaling back the normalized FeNO using the baseline correction factor to determine the FeNO of the patient.

2. The method of claim 1 wherein measuring an FeNO concentration comprises measuring FeNO concentration as a function of time.

3. The method of claim 1 wherein measuring an FeNO concentration comprises collecting a sample of exhaled gases and thereafter measuring FeNO concentration of the sample.

4. The method of claim 2 further comprising collecting the exhaled gases as a sample and thereafter measuring an FeNO concentration of the sample.

5. The method of claim 4 wherein the sample is collected in a bag.

6. The method of claim 4 wherein the sample is collected in a cylinder with a piston.

7. The method of claim 1 wherein adjusting the normalized FeNO is based on a range around the selected flow rate.

8. The method of claim 7 wherein the selected flow rate is approximately 50 ml/sec.

9. A nitric oxide (NO) monitoring system comprising:

at least one processor; and

at least one memory, communicatively coupled to the at least one processor and storing instructions that, when executed by the processor, cause the NO monitoring system to perform a method of determining exhaled nitric oxide (FeNO) for a subject, the method comprising:

collecting exhaled gases from the subject;

measuring FeNO in the collected exhaled gases;

measuring a flow rate of the exhaled gases as a function of time;

determining an average flow rate of the exhaled gases based on the measured flow rate of exhaled gases as a function of time;

calculating a baseline correction factor “X” according to the formula:

X=A/B where A is the measured FeNO at the average flow rate; and B is FeNO for a normal subject at the average flow rate;

normalizing the measured FeNO using the baseline correction factor X to obtain a normalized FeNO;

adjusting the normalized FeNO to a selected flow rate; and

scaling back the normalized FeNO using the baseline correction factor;

thereby determining FeNO for the subject.

10. The system of claim 9 wherein the selected flow rate is about 50 ml/sec.

11. The system of claim 9 wherein the exhaled gases are exhaled at a substantially constant flow rate.

12. The system of claim 11 wherein the substantially constant flow rate is based at least in part on a standard.

13. The system of claim 11 wherein the substantially constant flow rate is about 50 ml/sec±10 ml/sec.