Method and apparatus for the measurement of cardiac output

• US 6,348,038 B1
• Filed: 03/28/2000
• Issued: 02/19/2002
• Est. Priority Date: 07/10/1997
• Status: Expired due to Term

• Current Assignee: Lidco Group, PLC (Masimo Corporation)
• Original Assignee: Monitoring Technology Corporation
• Inventors: OʼBrien, Terence Kevin, Linton, Robert Anthony Fox, Linton, Nicholas William Fox, Band, David Marston
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US09/462,073
• Time in Patent Office: 693 Days
• Field of Search: 600/485, 600/486, 600/500, 600/526
• US Class Current: 600/485
• 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 5/7257 using Fourier transforms

Abstract

A method for the measurement of cardiac output in a patient in which the arterial blood pressure waveform of a patient from a blood pressure monitoring device over a period of time is subjected to various transformations and corrections, including a Fourier analysis in order to obtain the modulus of the first harmonic. The nominal stroke volume is then determined from the first harmonic and data relating to the arterial blood pressure and heart rate. The nominal cardiac output is then obtained from the nominal stroke volume.

Claims

1. A method for the measurement of cardiac output in a patient, which method comprises the steps of:

(i) recording and storing the arterial blood pressure waveform of a patient from a blood pressure monitoring device over a period of time;

(ii) subjecting the data obtained in step (i) to Fourier analysis in order to obtain the modulus of the first harmonic;

(iii) determining the nominal stroke volume from the modulus of the first harmonic obtained in step (ii) and data relating to the arterial blood pressure and the heart rate; and

(iv) obtaining the nominal cardiac output and/or the systemic vascular resistance from data obtained in step (iii).

2. A method as claimed in claim 1 wherein the arterial blood pressure is recorded and stored in step (i) for a period of up to ten seconds.

3. A method as claimed in claim 2 wherein the arterial blood pressure is recorded and stored in step (i) for a period of up to four seconds.

4. A method as claimed in claim 1 wherein the arterial blood pressure is analysed on a beat-by-beat basis.

5. A method as claimed in claim 1, wherein the nominal stroke volume is obtained from the following equation:

$\mathrm{nominal}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{stroke}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{volume}=\frac{\text{ <br><br> <br><br>modulus <br><br> <br><br>of <br><br> <br><br>first <br><br> <br><br>harmonicof <br><br> <br><br>blood <br><br> <br><br>pressure <br><br> <br><br>waveform}}{{\mathrm{<br><br>}}^{+0.0092\times <br><br>\mathrm{MAP}}\times <br><br>\mathrm{HR}}$

where e is the base of natural logarithms and MAP is the mean arterial blood pressure.

6. A method as claimed in claims 1, wherein an augmentation index is included in the calculation of the nominal stroke volume in step (iii).

7. A method as claimed in claim 1 wherein the nominal cardiac output is obtained by multiplying the nominal stroke volume by the heart rate.

9. A method as claimed in claim 7 wherein the arterial blood pressure is recorded and stored in step (a) for a period of up to ten seconds.

10. A method as claimed in claim 9 wherein the arterial blood pressure is recorded and stored in step (a) for a period of up to four seconds.

8. A method for the measurement of cardiac output in a patient, which method comprises the steps of:

(a) recording and storing the arterial blood pressure waveform of a patient from a blood pressure monitoring device over a period of time;

(b) subjecting the waveform obtained in step (a) to a non-linear transformation that corrects for the variation of the characteristics of the arterial system with pressure;

(c) subjecting the data obtained in step (b) to Fourier analysis in order to obtain the modulus of the first harmonic;

(d) determining the nominal stroke volume from the modulus of the first harmonic obtained in step (c) and data relating to the heart rate and optionally the arterial blood pressure; and

(e) obtaining the nominal cardiac output and/or the systemic vascular resistance from data obtained in step (d).

11. A method as claimed in claim 8 wherein the arterial blood pressure is analysed on a beat-by-beat basis.

12. A method as claimed in claim 8 wherein the transformation in step (b) is effected using a look up table, with the mean of the data then being found and subtracted.

13. A method as claimed in claim 8 wherein the nominal stroke volume is obtained from the following equation:

$\mathrm{nominal}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{stroke}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{volume}=\frac{\text{ <br><br> <br><br>modulus <br><br> <br><br>of <br><br> <br><br>first <br><br> <br><br>harmonicof <br><br> <br><br>blood <br><br> <br><br>pressure <br><br> <br><br>waveform}}{{\mathrm{<br><br>}}^{+0.0092\times <br><br>\mathrm{MAP}}\times <br><br>\mathrm{HR}}$

14. A method as claimed in claim 8 wherein an augmentation index is included in the calculation of the nominal stroke volume in step (iii).

15. An apparatus for the measurement of cardiac output in a patient, which comprises:

(1) means for recording and storing the arterial blood pressure waveform of a patient from a blood pressure monitoring device over a period of time;

(2) means for Fourier analysis of the arterial blood pressure waveform to obtain the modulus of the first harmonic;

(3) means for deriving the nominal stroke volume from the modulus of the first harmonic and data relating to the arterial blood pressure and the heart rate; and

(4) means for calculating the nominal cardiac output and/or the systemic vascular resistance.

16. An apparatus for the measurement of cardiac output in a patient, which method comprises the steps of:

(A) means for recording and storing the arterial blood pressure waveform of a patient from a blood pressure monitoring device over a period of time;

(B) means for transforming the arterial blood pressure waveform to correct for the variation of the characteristics of the arterial system with pressure;

(C) means for the Fourier analysis of the transformed data to obtain the modulus of the first harmonic of the waveform;

(D) means for determining the nominal stroke volume from the modulus of the first harmonic and data relating to the heart rate and optionally the arterial blood pressure; and

(E) means for calculating the nominal cardiac output and/or the systemic vascular resistance.