Method of assessment of airway variability in airway hyperresponsiveness

• US 20050247307A1
• Filed: 05/04/2005
• Published: 11/10/2005
• Est. Priority Date: 05/04/2004
• Status: Active Grant

• Current Assignee: THORASYS Thoracic Medical Systems Inc.
• Original Assignee: Dalhousie University
• Inventors: Maksym, Geoffrey N., Lall, Carolyn A.
• Granted Patent: US 8,172,765 B2
• Time in Patent Office: Days
• US Class Current: 128/200.230
• CPC Class Codes: A61B 5/085 Measuring impedance of respiratory organs or lung elasticity
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/4884 inducing physiological or psychological stress, e.g. applications for stress testing
• CPC Class Codes: G16H 40/63 for local operation
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

The invention relates to a method of assessing airway variability in airway responsiveness or asthma by measuring the variation of resistance (Rrs) by a forced oscillation technique utilizing either a single or a plurality of input frequencies during a plurality of respiratory cycles of a patient; calculating the statistical variability of the Rrs for the patient; and, correlating the statistical variability of the Rrs of the patient to a standard curve to quantify the degree of asthma of the patient. The invention also enables the effectiveness of a bronchoactive agent to be measured.

Claims

1. A method of assessment of airway variability in airway responsiveness or asthma comprising the steps of:

measuring the variation of resistance (Rrs) by a forced oscillation technique utilizing either a single or a plurality of input frequencies during a plurality of respiratory cycles of a patient;

calculating the statistical variability of the Rrs for the patient; and

,

correlating the statistical variability of the Rrs of the patient to a standard curve to quantify the degree of asthma of the patient.

2. A method as in claim 1 wherein calculating the statistical variability of the Rrs is a calculation of any one of or a combination of standard deviation or high/low Rrs measurements.

11. A method as in claim 1 further comprising the steps of determining the noise level and the signal to noise ratio contributing to the assessment of airway resistance variability for each oscillation frequency of the pressure oscillations, including:

obtaining the coherence of the pressure with flow signals;

obtaining a Fourier transform of multiple cycles of pressure and a Fourier transform of multiple cycles of flow;

obtaining the absolute value of the pressure and flow signals at each frequency of oscillation;

obtaining the average of the absolute values of the pressure and flow signals for a region of frequencies adjacent to the oscillation frequencies not including any oscillation frequencies that the signal to noise ratio for either pressure or flow is the ratio of the signal, determined as the magnitude of the pressure or flow at the oscillation frequency, divided by the noise, determined as the magnitude of the pressure or flow in a region of frequencies adjacent to the oscillation frequency not including any oscillation frequency.

3. A method of determining the effectiveness of a pharmacological agonist or antagonist on altering airway diameter variability comprising the steps of:

measuring the variation of resistance (Rrs) by a forced oscillation technique utilizing a plurality of input frequencies during a plurality of respiratory cycles of a patient;

measuring the variation of resistance (Rrs) by a forced oscillation technique utilizing a plurality of input frequencies during a plurality of respiratory cycles of a patient having been administered a pharmacological agonist or antagonist;

calculating the statistical variability of the Rrs for the patient for each of the first two steps; and

,

comparing the statistical variability of the Rrs to determine the effectiveness of the pharmacological agonist or antagonist.

4. A method as in claim 3 wherein the pharmacological agonist or antagonist is a bronchodilator.

5. A method as in claim 3 wherein the pharmacological agonist or antagonist is a bronchoconstrictor.

6. A method of determining the effectiveness of a pharmacological agonist or antagonist on altering airway diameter variability comprising the steps of:

measuring the variation of reactance (Xrs) by a forced oscillation technique utilizing a plurality of input frequencies during a plurality of respiratory cycles of a patient both pre- and post-administration of a pharmacological agonist or antagonist;

calculating the Xrs for the patient for each of the pre- and post-administration steps; and

,

comparing Xrs to determine the effectiveness of the pharmacological agonist or antagonist.

7. A method as in claim 6 wherein the pharmacological agonist or antagonist is a bronchodilator.

8. A method as in claim 6 wherein the pharmacological agonist or antagonist is a bronchoconstrictor.

9. A method as in claim 6 where the impedance of the measuring device is removed by a compensation algorithm.

10. A method as in claim 6 wherein the effectiveness of a pharmacological agonist or antagonist is determined by a comparison of any one of or a combination of standard deviation of Rrs or high/low Rrs measurements or Xrs measurements between pre- and post-pharmacological agonist or antagonist administration in a patient.

12. A method for determining baseline values of variations of resistance (Rrs), variations in reactance (Xrs) and standard deviation of resistance (SDRrs) and the changes in these values in response to bronchoactive agents comprising the steps of:

a. measuring and storing closed impedance (Zc);

b. measuring and storing open impedance (Zo)

c. Measuring and compensating baseline subject impedance Zm(t) over several cycles to determine Zrs(t);

d. Measuring and comparing Rrs, Xrs and variations in Rrs and Xrs;

e. Administering a broncho active agent to a patient;

f. Measuring post drug impedance Zm p and compensating to determine Zrs_p;

g. calculating post-drug and pre-drug Rrs, Xrs and variation in Rrs and Xrs;

h. comparing post-drug and pre-drug values of Rrs, Xrs and variations in Rrs and Xrs to standard values to determine if the Rrs, Xrs and variation in Xrs and Rrs are normal or abnormal.