Measuring central pressure with brachial cuff

• US 9,974,450 B2
• Filed: 03/22/2016
• Issued: 05/22/2018
• Est. Priority Date: 05/07/2010
• Status: Active Grant

• Current Assignee: Atcor Medical Pty Ltd (CardieX Ltd.)
• Original Assignee: Atcor Medical Pty Ltd (CardieX Ltd.)
• Inventors: Qasem, Ahmad M.
• Primary Examiner(s): Mallari, Patricia
• Assistant Examiner(s): TOTH, KAREN E
• Application Number:
  US15/077,371
• Publication Number:
  US 20160198959A1
• Time in Patent Office: 791 Days
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/0225 the pressure being controlled by electric signals, e.g. derived from Korotkoff sounds
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7253 characterised by using transforms
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence
• CPC Class Codes: G16H 10/40 for data related to laboratory analysis, e.g. patient specimen analysis
• CPC Class Codes: G16H 50/30 for calculating health indices; for individual health risk assessment
• CPC Class Codes: G16Z 99/00 Subject matter not provided for in other main groups of this subclass

Abstract

A method for determining a calibrated aortic pressure waveform from a brachial cuff waveform involves the use of one or more generalized transfer functions. The one or more generalized transfer functions are specific for predetermined brachial cuff pressure ranges, such as below diastolic pressure, between diastolic and systolic pressure, and above systolic pressure. The brachial cuff is inflated to a pressure within the pressure range appropriate for the generalized transfer function to be applied to the brachial cuff waveform to generate the aortic pressure waveform. In some circumstances, it may be necessary to use a calibration transfer function to generate a calibrated aortic waveform. In other circumstances, the calibration transfer function is not necessary.

Claims

1. A blood pressure measuring system for determining a calibrated aortic pressure waveform with cardiovascular waveform features preserved, the system comprising:

a brachial cuff device having a brachial cuff, a tube, a pressure pump with a control unit, and a pressure sensor that provides an analog signal, said brachial cuff device being capable of measuring a patient'"'"'s brachial systolic pressure (SP_B) and brachial diastolic pressure (DP_B) by oscillometric technique;

the control unit controlling the inflation of the brachial cuff around a patient'"'"'s upper arm to a constant pressure within a predetermined pressure range, wherein the predetermined pressure range is one of less than the patient'"'"'s brachial diastolic pressure DP_B as measured by the brachial cuff device by oscillometric technique, between the patient'"'"'s brachial diastolic pressure DP_B and the brachial systolic pressure SP_B as measured by the brachial cuff device by oscillometric technique, and above the patient'"'"'s brachial systolic pressure SP_B as measured by the brachial cuff device by oscillometric technique;

a digital signal processor comprising a low pass filter and a high pass filter that receives the analog signal from the pressure sensor when the cuff pressure is maintained at a constant pressure within the predetermined pressure range and outputs a digital brachial cuff signal containing filtered data that preserves cardiovascular waveform features of the patient'"'"'s brachial cuff volumetric displacement waveform; and

software on a computer that calibrates the brachial cuff volumetric displacement waveform using at least two of the patient'"'"'s brachial systolic pressure (SP_B) as measured by the brachial cuff device by oscillometric technique, the patient'"'"'s brachial mean pressure (MP_B) and the patient'"'"'s brachial diastolic pressure (DP_B) as measured by the brachial cuff device by oscillometric technique, wherein the patient'"'"'s brachial mean pressure (MP_B) if used is calculated by the brachial cuff device based on measured values for the patient'"'"'s brachial systolic pressure (SP_B) and the patient'"'"'s brachial diastolic pressure (DP_B), and the software further converts the calibrated brachial cuff volumetric displacement waveform with cardiovascular waveform features preserved to a calibrated aortic pressure waveform with cardiovascular waveform features preserved by using one or more generalized transfer functions, wherein one or more generalized transfer functions comprise at least a first generalized transfer function that transforms the calibrated brachial cuff waveform to an intermediate artery pressure waveform and a second generalized transfer function that transforms the intermediate artery pressure waveform to an aortic pressure waveform;

wherein each of the one or more generalized transfer functions are determined specifically for application to a calibrated brachial cuff volumetric displacement waveform measured by the brachial cuff inflated to a pressure within the predetermined pressure range, said one or more generalized transfer functions representing the harmonic ratio in amplitude and phase to transform the calibrated brachial cuff volumetric displacement waveform with cardiovascular waveform features preserved to the calibrated aortic pressure waveform with cardiovascular waveform features preserved when the brachial cuff is inflated to a pressure within the selected pressure range.

2. A blood pressure measuring system as recited in claim 1 wherein software also uses a generalized calibration transfer function to reduce error in the estimation of aortic systolic pressure, which would be introduced by calibrating the cuff volume pulse with the measured brachial SP_B and DP_B values.

3. A blood pressure measuring system as recited in claim 1 wherein the predetermined pressure range is 10-90% of the diastolic pressure (DP_B).

4. A blood pressure measuring system as recited in claim 1 further comprising multiple generalized transfer functions each being based on cuff pressures within a predetermined pressure range.

5. A blood pressure measuring system as recited in claim 1 wherein the predetermined pressure range is between SP_B and DP_B and cuff pressure is defined by the following equation

P_Cuff=(K%)(SP_B−

DP_B)+DP_B

where K % is chosen to be between 10 and 90%.

6. A blood pressure measuring system as recited in claim 1 wherein the predetermined pressure range is above SP_B and the cuff pressure is in the following range

P_Cuff=[(K%)+1]SP_B

where K % ranges from 10 to 90%.

7. A blood pressure measuring system as recited in claim 1 wherein the calibrated brachial cuff waveform that is converted using one or more generalized transfer functions to the calibrated aortic pressure waveform with its cardiovascular waveform features preserved comprises an average of multiple recorded and calibrated brachial cuff waveforms measured by the inflated cuff around the patient'"'"'s upper arm.

8. In a blood pressure measuring system, a method for determining a calibrated aortic pressure waveform having cardiovascular waveform features preserved, the method comprising the steps:

providing an inflatable brachial cuff having a pressure sensor to measure pressure within the brachial cuff, said pressure sensor outputting an analog signal;

providing a digital signal processor that receives the analog signal from the pressure sensor and is configured to output a digital brachial cuff signal containing filtered digital data that preserves the cardiovascular waveform features of the patient'"'"'s brachial cuff volumetric displacement waveform;

measuring at least the patient'"'"'s brachial systolic pressure (SP_B) and brachial diastolic pressure (DP_B) using the brachial cuff in an oscillometric mode;

inflating the brachial cuff around a patient'"'"'s upper arm to a constant pressure that is between the measured DP_B and the measured SP_B;

maintaining the brachial cuff at said constant pressure and acquiring the analog signal from the cuff pressure sensor;

filtering and converting the acquired analog signal to generate filtered digital data that preserves the cardiovascular waveform features of the patient'"'"'s brachial cuff volumetric displacement waveform, and recording the filtered data that preserves the cardiovascular waveform features of the patient'"'"'s brachial cuff volumetric displacement waveform;

using at least two of brachial systolic pressure (SP_B), brachial mean pressure (MP_B) and brachial diastolic pressure (DP_B) to calibrate the recorded brachial cuff waveform, wherein brachial mean pressure (MP_B), if used, is determined from the measured brachial systolic pressure (SP_B) and the measured brachial diastolic pressure (DP_B); and

using one or more generalized transfer functions to convert the calibrated, recorded brachial cuff waveform to a calibrated aortic pressure waveform having its cardiovascular waveform features preserved, wherein said one or more generalized transfer functions represent the harmonic ratio in amplitude and phase to transform the calibrated brachial cuff volumetric displacement waveform having cardiovascular waveform features preserved to the calibrated aortic pressure waveform having cardiovascular waveform features preserved when the brachial cuff is inflated to a pressure between the patient'"'"'s measured diastolic pressure (DP_B) and the patient'"'"'s measured systolic pressure (SP_B) and further wherein one or more generalized transfer functions comprise at least a first generalized transfer function that mathematically transforms the calibrated brachial cuff waveform to an intermediate artery pressure waveform and a second generalized transfer function that transforms the intermediate artery pressure waveform to an aortic pressure waveform.

9. A method as recited in claim 8 further comprising the step of displaying the calibrated aortic pressure waveform as a trace or otherwise on a computer display screen.

10. A method for determining a calibrated aortic pressure waveform as recited in claim 8 wherein the brachial cuff is inflated around the patient'"'"'s upper arm to a constant pressure that is defined by the following equation

P_Cuff=(K%)(SP_B−

DP_B)+DP_B

where K % is chosen to be between 10% and 90%.

11. A method of determining a calibrated aortic pressure waveform as recited in claim 8 wherein the one or more generalized transfer functions are estimated from simultaneously recorded data for a general population.

12. A method as recited in claim 8 wherein the calibrated brachial cuff waveform that is converted using one or more generalized transfer functions to the calibrated aortic pressure waveform with its cardiovascular waveform features preserved comprises an average of multiple recorded and calibrated brachial cuff waveforms measured by the inflated cuff around the patient'"'"'s upper arm.

13. A method of determining a calibrated aortic pressure waveform as recited in claim 8 wherein the brachial cuff is part of a device that comprises the brachial cuff, a tube, a pressure pump with a pressure control system, and a pressure sensor that provides an analog signal and the blood pressure measuring system further comprises the digital signal processor that has a low pass filter and a high pass filter, receives the analog signal from the pressure sensor and outputs a digital brachial cuff signal containing filtered data preserving the cardiovascular waveform features of patient'"'"'s brachial cuff volumetric displacement waveform, and a computer that receives the digital brachial cuff signal, records and calibrates the brachial cuff waveform, and converts the calibrated brachial cuff waveform to the calibrated aortic pressure waveform having cardiovascular waveform features preserved using said one or more generalized transfer functions representing the harmonic ratio in amplitude and phase to transform a calibrated brachial cuff volumetric displacement waveform having cardiovascular waveform features preserved to the calibrated aortic pressure waveform having cardiovascular waveform features preserved when the brachial cuff is inflated to a pressure between the patient'"'"'s measured diastolic pressure (DP_B) and the patient'"'"'s measured systolic pressure (SP_B).

14. A method of determining a calibrated aortic pressure waveform as recited in claim 8 wherein the calibrated, recorded brachial cuff waveform that is converted to a calibrated aortic pressure waveform having its cardiovascular waveform features preserved is an average of multiple calibrated, recorded brachial cuff waveforms.

15. A method of determining a calibrated aortic pressure waveform as recited in claim 8 wherein the one or more generalized transfer functions are implemented by software on a computer.