Apnea/hypopnea detection system and method

• US 20050020932A1
• Filed: 07/21/2004
• Published: 01/27/2005
• Est. Priority Date: 07/25/2003
• Status: Active Grant

• Current Assignee: Philips RS North America LLC (Koninklijke Philips N.V.)
• Original Assignee: RIC INVESTMENTS LLC (Koninklijke Philips N.V.)
• Inventors: Shankar, Uday S., Haberland, Ben
• Granted Patent: US 7,118,536 B2
• Time in Patent Office: Days
• US Class Current: 600/538
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/4818 Sleep apnoea

Abstract

An apnea/hypopnea detection system and method that monitors a patient'"'"'s respiratory flow, determines (a) a long term RMS energy based on the flow, (b) a long term threshold determined based on the long term RMS energy, and (c) a short term RMS energy based on the flow. Determining whether the patient is experiencing an apnea/hypopnea is accomplished by comparing the short term RMS energy with the long term threshold. This A/H detection technique is useful in diagnosing a patient for a breathing disorder, such as OSA, and/or for controlling an auto-titration pressure support system.

Claims

1. An apnea/hypopnea detection system comprising:

a flow sensor adapted to detect patient respiratory flow; and

processing means for (1) determining (a) a long term RMS energy based on the flow, (b) a long term threshold determined based on the long term RMS energy, and (c) a short term RMS energy based on the flow, and for (2) determining whether a patient is experiencing an apnea/hypopnea event by comparing the short term RMS energy with the long term threshold.

2. The system of claim 1, wherein determining the long term threshold includes multiplying the long term RMS energy by an entry threshold fraction.

3. The system of claim 1, wherein determining whether a patient is experiencing an apnea/hypopnea event includes determining whether the short term RMS energy falls below the long term threshold.

4. The system of claim 1, wherein the processing means also calculates a short term integral of the patient flow and a long term integral of the patient flow, and determines an absolute difference therebetween, and wherein determining whether a patient is experiencing an apnea/hypopnea event includes comparing the absolute difference to a differential threshold.

5. The system of claim 4, wherein the differential threshold is an empirically determined value.

6. The system of claim 1, wherein the processing means also determines whether such a patient has ceased experiencing an apnea/hypopnea event.

7. The system of claim 6, wherein determining whether such a patient has ceased experiencing an apnea/hypopnea event includes calculating an exit threshold and comparing the short term RMS energy with the exit threshold.

8. The system of claim 7, wherein the processing means determines the exit threshold based on the long term threshold.

9. The system of claim 1, wherein the processing means the short term RMS energy, S_RMS(n), as:

$S_{\mathrm{RMS}}<br><br>\left(n\right)=\sqrt{\frac{1}{N_S}*\underset{k=0}{\overset{N_S-1}{\sum <br><br>}}<br><br>{\left[Q<br><br>\left(n-k\right)\right]}^2},$

where N_S=T_S−

f, Q(n) is the patient flow, n is processing cycle, f is the sampling frequency, and T_S is a period of time over which the short term RMS values is calculated.

10. The system of claim 1, wherein the processing means the long term RMS energy L_RMS(n) as:

$L_{\mathrm{RMS}}<br><br>\left(n\right)=\sqrt{\frac{1}{N_L}*\underset{k=0}{\overset{N_L-1}{\sum <br><br>}}<br><br>{\left[Q<br><br>\left(n-k\right)\right]}^2}$

where N_L=T_S−

f, Q(n) is the patient flow, n is processing cycle, f is the sampling frequency, and T_L is a period of time over which the long term RMS values is calculated.

11. The system of claim 1, wherein the long term integral energy L_I(n) is determined as:

$L_I<br><br>\left(n\right)=\underset{k=0}{\overset{N_L-1}{\sum <br><br>}}<br><br>Q<br><br>\left(n-k\right)$

where N_L=T_S−

f, Q(n) is the patient flow, n is processing cycle, f is the sampling frequency, and T_L is a period of time over which the long term RMS values is calculated.

12. The system of claim 1, wherein the short term integral energy S_I(n) is determined as:

$S_I<br><br>\left(n\right)=\underset{k=0}{\overset{N_S-1}{\sum <br><br>}}<br><br>Q<br><br>\left(n-k\right)$

where N_S=T_S−

f, Q(n) is the patient flow, n is processing cycle, f is the sampling frequency, and T_S is a period of time over which the short term RMS values is calculated.

13. The system of claim 1, further comprising a conduit coupled to an airway of such a patient, and wherein the flow sensor is coupled to the conduit.

14. The system of claim 1, further comprising a pressure generating system adapted to generate a flow of gas, and wherein the processing means controls a pressure of a flow of gas output of the pressure generating system based on whether such a patient is experiencing the apnea/hypopnea event.

15. A method of detecting an apnea/hypopnea comprising:

monitoring a patient'"'"'s respiratory flow;

determining a long term RMS energy based on the flow;

determining a long term threshold based on the long term RMS energy;

determining a short term RMS energy based on the flow; and

comparing the short term RMS energy with the long term threshold to determine whether such a patient is experiencing an apnea/hypopnea.

16. The method of claim 15, wherein determining the long term threshold includes multiplying the long term RMS energy by an entry threshold fraction.

17. The method of claim 15, wherein determining whether a patient is experiencing an apnea/hypopnea event includes determining whether the short term RMS energy falls below the long term threshold.

18. The method of claim 15, further comprising:

determining a short term integral of the respiratory flow;

determining a long term integral of the respiratory flow; and

determines an absolute difference between the short term integral of respiratory flow and the long term integral of respiratory flow; and

wherein determining whether a patient is experiencing an apnea/hypopnea event includes comparing the absolute difference to a differential threshold.

19. The method of claim 15, further comprising determining whether such a patient has ceased experiencing an apnea/hypopnea event.

20. The method of claim 19, wherein determining whether such a patient has ceased experiencing an apnea/hypopnea event comprises calculating an exit threshold and comparing the short term RMS energy with the exit threshold.

21. The method of claim 20, wherein the exit threshold is determined based on the long term threshold.

22. The method of claim 15, wherein the short term RMS energy S_RMS(n) is determined as:

$S_{\mathrm{RMS}}<br><br>\left(n\right)=\sqrt{\frac{1}{N_S}*\underset{k=0}{\overset{N_S-1}{\sum <br><br>}}<br><br>{\left[Q<br><br>\left(n-k\right)\right]}^2},$

where N_S=T_S−

f, Q(n) is the patient flow, n is processing cycle, f is the sampling frequency, and T_S is a period of time over which the short term RMS values is calculated.

23. The method of claim 15, wherein the long term RMS energy L_RMS(n) is determined as:

$L_{\mathrm{RMS}}<br><br>\left(n\right)=\sqrt{\frac{1}{N_L}*\underset{k=0}{\overset{N_L-1}{\sum <br><br>}}<br><br>{\left[Q<br><br>\left(n-k\right)\right]}^2}$

where N_L=T_S−

f, Q(n) is the patient flow, n is processing cycle, f is the sampling frequency, and T_L is a period of time over which the long term RMS values is calculated.

24. The method of claim 15, wherein the long term integral energy L_I(n) is determined as:

$L_I<br><br>\left(n\right)=\underset{k=0}{\overset{N_L-1}{\sum <br><br>}}<br><br>Q<br><br>\left(n-k\right)$

where N_L=T_S−

f, Q(n) is the patient flow, n is processing cycle, f is the sampling frequency, and T_L is a period of time over which the long term RMS values is calculated.

25. The method of claim 15, wherein the short term integral energy S_I(n) is determined as:

$S_I<br><br>\left(n\right)=\underset{k=0}{\overset{N_S-1}{\sum <br><br>}}<br><br>Q<br><br>\left(n-k\right)$

where N_S=T_S−

f, Q(n) is the patient flow, n is processing cycle, f is the sampling frequency, and T_S is a period of time over which the short term RMS values is calculated.

26. The method of claim 15, wherein monitoring a patient'"'"'s respiratory flow comprises:

providing a conduit coupled to an airway of such a patient; and

providing a flow sensor is coupled to the conduit.

27. The method of claim 15, further comprising:

providing a pressure generating system adapted to generate a flow of gas; and

controlling a pressure of a flow of gas output of the pressure generating system based on whether such a patient is experiencing the apnea/hypopnea event.