APPARATUS AND METHOD FOR MONITORING PRESSURE RELATED CHANGES IN THE EXTRA-THORACIC ARTERIAL CIRCULATORY SYSTEM

• US 20140276120A1
• Filed: 12/18/2012
• Published: 09/18/2014
• Est. Priority Date: 12/01/2003
• Status: Abandoned Application

• Current Assignee: RIC INVESTMENTS LLC (Respironics Incorporated)
• Original Assignee: RIC INVESTMENTS LLC (Respironics Incorporated)
• Inventors: STARR, Eric W., SCULL, James A., AYERS, Eric, HETE, Bernie F., WILCZEK, Donald S., SANDERS, Mark H.
• Application Number:
  US13/718,423
• Publication Number:
  US 20140276120A1
• Time in Patent Office: Days
• US Class Current: 600/480
• CPC Class Codes: A61B 5/0082 adapted for particular medical purposes
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/02427 Details of sensor
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

A method and apparatus for monitoring changes in the intra-thoracic pressure of a patient due to the patient'"'"'s respiratory activity or volumetric changes in the extra-thoracic arterial circulatory system due to cardiac function based on the changes in pressure in the patient'"'"'s extra-thoracic arterial circulatory system as measured by a plethysmography sensor, such as an photoplethysmograph. A frequency spectrum is generated for the plethysmograph signal and the frequencies of interest is isolated from the frequency spectrum by setting appropriate cutoff frequencies for the frequency spectrum. This isolated frequency is used to filter the plethysmograph signal to provide a signal indicative of the patient'"'"'s respiratory activity or cardiac function.

Claims

1. A non-invasive cardiac monitoring method comprising:

passing light through a portion of a patient'"'"'s extra-thoracic arterial circulation;

receiving light after having been passed through such a patient;

outputting a first signal based on the received light; and

producing a cardiac pressure signal as a measure of such a patient'"'"'s cardiac function by isolating cardiac related pressure variations in the first signal.

2. The method according to claim 1, wherein the cardiac pressure signal is determined substantially continuously.

3. The method according to claim 1, further comprising outputting the cardiac pressure signal in a human perceivable format.

4. The method according to claim 1, wherein producing a thoracic pressure signal comprises:

determining frequency components of the first signal;

identifying a heart rate frequency component (f_HR) from the frequency components of the first signal; and

filtering the first signal based on the heart rate frequency component f_HR so as to isolate the heart rate frequency component f_HR from the first signal to produce the cardiac pressure signal.

5. The method according to claim 4, wherein determining frequency components of the first signal includes analyzing the first signal with a Fourier transform that generates the frequency components of the first signal.

6. The method according to claim 4, wherein producing a cardiac pressure signal further comprises removing any offset in the frequency components of the first signal.

7. The method according to claim 4, further comprising determining a heart rate of such a patient via a heart rate monitor, and wherein identifying the heart rate frequency component f_HR from the frequency components of the first signal is accomplished based on the output of the heart rate monitor.

8. The method according to claim 1, wherein producing a thoracic pressure signal comprises:

determining frequency components of the first signal;

identifying a respiratory rate frequency component f_RR from the frequency components of the first signal; and

filtering the physiologic signal based on the respiratory rate frequency component f_RR so as to remove the respiratory rate frequency component f_HR from the physiologic signal, thereby isolating a heart rate frequency component f_HR of the first signal to produce the thoracic pressure signal.

9. The method according to claim 8, further comprising determining a respiratory rate of such a patient via a respiratory rate monitor, and wherein identifying the respiratory rate frequency component f_RR from the frequency components of the first signal is accomplished based on the output of the respiratory monitor.

10. The method according to claim 1, wherein producing a thoracic pressure signal comprises:

determining frequency components of the first signal, including a respiratory rate frequency component f_RR and a heart rate frequency component f_HR;

identifying a respiratory rate frequency component f_RR from the frequency components of the first signal;

identifying a heart rate frequency component f_HR from the frequency components of the first signal; and

filtering the first signal based on the respiratory rate frequency component f_RR and the heart rate frequency component f_HR so as to isolate the heart rate frequency component f_RR from the first signal to produce the cardiac pressure signal.

11. The method according to claim 10, wherein filtering the first signal includes:

(1) setting a cutoff frequency (f_cutoff) as f_HR−

f_smear responsive to the respiratory rate frequency component f_RR being less than the heart rate frequency component f_HR,

(2) setting the cutoff frequency (f_cutoff) as f_HR+f_smear responsive to the rate frequency component f_RR being greater than the heart rate frequency component f_HR, where f_smear is a predetermined threshold frequency, and

(3) high pass filtering the first signal at the cutoff frequency f_cutoff.

12. The method according to claim 10, further comprising:

determining a respiratory rate of such a patient via a respiratory rate monitor, and wherein identifying the respiratory rate frequency component f_RR from the frequency components of the first signal is accomplished based on the output of the respiratory rate monitor; and

determining a heart rate of such a patient based on a heart rate monitor, and wherein identifying the heart rate frequency component f_HR from the frequency components of the first signal is accomplished based on the output of the heart rate monitor.

13. The system according to claim 1, further comprising identifying an occurrence of at least one of pulsus paradoxis, pulsus alternans, pulsus bisferiens, dicrotic pulse, anacrotic pulse, “

waterhammer”

pulse or a normal pulse based on the cardiac pressure signal.