Method and apparatus for producing a central pressure waveform in an oscillometric blood pressure system

• US 9,433,358 B2
• Filed: 12/07/2009
• Issued: 09/06/2016
• Est. Priority Date: 02/21/2006
• Status: Active Grant

• Current Assignee: Uscom Ltd.
• Original Assignee: Uscom Ltd.
• Inventors: Lowe, Andrew
• Primary Examiner(s): Natnithithadha, Navin
• Application Number:
  US12/632,003
• Publication Number:
  US 20100152593A1
• Time in Patent Office: 2,465 Days
• Field of Search: 600/481, 600/483, 600/485, 600490-507
• US Class Current: 1/1
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/02225 using the oscillometric method
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/412 Detecting or monitoring sepsis
• CPC Class Codes: A61B 7/00 Instruments for auscultation
• CPC Class Codes: A61B 7/04 Electric stethoscopes microphones, acoustic transducers therefor H04R
• CPC Class Codes: G06F 2218/10 by analysing the shape of a waveform, e.g. extracting parameters relating to peaks
• CPC Class Codes: G16H 40/63 for local operation

Abstract

A central arterial blood pressure waveform is developed from pressure waveforms obtained from proximal and distal blood pressure cuffs on the brachial artery of an arm that are inflated to a supra-systolic pressure, The proximal and distal cuff pressure waveforms associated with at least one cardiac ejection cycle are sensed, The propagation times of a blood pressure pulse from the entry of the artery to the proximal cuff and from the proximal cuff to the distal cuff are calculated, permitting calculation of a reflection coefficient of the pressure pulse at one of the proximal and distal cuffs. Assuming a physical model of wave propagation along the artery between the aorta and the proximal and distal cuffs, an estimated pressure waveform at the opening of the artery can be determined.

Claims

1. A method of estimating an internal, central arterial blood pressure waveform from pressure waveforms obtained from at least one blood pressure cuff placed at two locations along a brachial artery of a patient'"'"'s arm, based on a physical model of the artery, said method comprising the steps of:

a. inflating a proximal blood pressure cuff on the artery of the arm to a supra-systolic pressure;

b, sensing a proximal cuff pressure waveform associated With at least one cardiac ejection cycle;

c. inflating a distal blood pressure cuff on the artery of the arm to a supra-systolic pressure;

d. sensing a distal cuff pressure waveform associated with at least one cardiac ejection cycle;

e. using a processor, calculating the time of propagation of a blood pressure pulse from the entry of the said artery to the proximal cuff;

f. using said processor, calculating the time of propagation of a blood pressure pulse from the proximal cuff to the distal, cuff;

g. using said processor, calculating a reflection coefficient a blood pressure pulse at at least one of the proximal and distal cuffs; and

h. based on said physical model of wave propagation along said artery between an aorta and said proximal and distal blood pressure cuffs and using said processor, determining an estimated internal, central arterial blood pressure waveform at the opening of the said artery.

2. The method of claim 1, where the time of propagation of said blood pressure pulse from the proximal cuff to the distal cuff is calculated by taking the difference in time between the incidence of the blood pressure pulse at the proximal cuff and an identifiable point on a signal related to heart activity, taking the difference in time between the incidence of the blood pressure pulse at the distal cuff and an equivalent identifiable point on the same signal related to heart activity, and calculating the difference between the differences.

3. The method of claim 2, where the signal related to heart activity is measured using one of an ECG, heart sounds sensor, tonometer, photoplethysmograph and blood pressure cuff.

4. The method of claim 1, where the time of propagation of said blood pressure pulse from the entry of the said artery to the proximal cuff is calculated by taking the difference in time between the incidence of the blood pressure pulse at the proximal cuff and an identifiable point on a signal related to the entry of a pressure pulse into the subclavian artery.

5. The method of claim 1, where the time of propagation of said blood pressure pulse from the entry of the said artery to the proximal cuff is calculated using a ratio of differences between frequency-domain representations of the proximal and distal pressure waveforms.

6. The Method of claim 5, where the ratio is given by:

7. The method of claim 4, where the signal related to heart activity is measured using one of a tonometer and a strain sensor, placed over one of the subclavian artery, and a carotid artery.

8. The method of claim 4, where the signal related to heart activity is measured using a heart sounds sensor, and the identifiable point is a time equal to the systolic ejection period prior to the incidence of the heart sounds.

9. The method of claim 4, where the signal related to heart activity is measured using an ECG, and the identifiable point is a predetermined time after the incidence of the R-wave.

10. The method of claim 1, where the reflection, coefficient of the pressure pulse at the proximal cuff is calculated according to a ratio between differences between time-shifted signals calculated from the cuff pressure waveforms.

11. The method of claim 10 where the ratio is given by:

12. The method of claim 1, where the reflection coefficient is a predetermined value.

13. The method of claim 1, where the time of propagation of said blood pressure pulse from the entry of the said artery to the proximal cuff is a predetermined value.