GB2404439A - Method of measuring a person's aortic blood pressure - Google Patents
Method of measuring a person's aortic blood pressure Download PDFInfo
- Publication number
- GB2404439A GB2404439A GB0317847A GB0317847A GB2404439A GB 2404439 A GB2404439 A GB 2404439A GB 0317847 A GB0317847 A GB 0317847A GB 0317847 A GB0317847 A GB 0317847A GB 2404439 A GB2404439 A GB 2404439A
- Authority
- GB
- United Kingdom
- Prior art keywords
- blood pressure
- person
- aortic
- extremity
- shape
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000036772 blood pressure Effects 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims abstract description 18
- 238000005259 measurement Methods 0.000 claims abstract description 19
- 238000012546 transfer Methods 0.000 claims description 13
- 230000003287 optical effect Effects 0.000 claims description 11
- 210000000624 ear auricle Anatomy 0.000 claims description 3
- XKZCXMNMUMGDJG-AWEZNQCLSA-N (2s)-3-[(6-acetylnaphthalen-2-yl)amino]-2-aminopropanoic acid Chemical compound C1=C(NC[C@H](N)C(O)=O)C=CC2=CC(C(=O)C)=CC=C21 XKZCXMNMUMGDJG-AWEZNQCLSA-N 0.000 claims description 2
- 210000003414 extremity Anatomy 0.000 description 7
- 230000035488 systolic blood pressure Effects 0.000 description 6
- 210000000709 aorta Anatomy 0.000 description 4
- 206010020772 Hypertension Diseases 0.000 description 3
- 230000004872 arterial blood pressure Effects 0.000 description 3
- 230000003750 conditioning effect Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 208000024172 Cardiovascular disease Diseases 0.000 description 2
- 210000001367 artery Anatomy 0.000 description 2
- 239000008280 blood Substances 0.000 description 2
- 210000004369 blood Anatomy 0.000 description 2
- 230000000747 cardiac effect Effects 0.000 description 2
- 230000035487 diastolic blood pressure Effects 0.000 description 2
- 210000002321 radial artery Anatomy 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 210000002302 brachial artery Anatomy 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000036651 mood Effects 0.000 description 1
- 230000010412 perfusion Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 210000000707 wrist Anatomy 0.000 description 1
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
- A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
- A61B5/6813—Specially adapted to be attached to a specific body part
- A61B5/6825—Hand
- A61B5/6826—Finger
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/021—Measuring pressure in heart or blood vessels
- A61B5/02108—Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics
- A61B5/02116—Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics of pulse wave amplitude
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/021—Measuring pressure in heart or blood vessels
- A61B5/022—Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
- A61B5/0225—Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers the pressure being controlled by electric signals, e.g. derived from Korotkoff sounds
- A61B5/02255—Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers the pressure being controlled by electric signals, e.g. derived from Korotkoff sounds the pressure being controlled by plethysmographic signals, e.g. derived from optical sensors
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
- A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
- A61B5/683—Means for maintaining contact with the body
- A61B5/6838—Clamps or clips
Landscapes
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Cardiology (AREA)
- Vascular Medicine (AREA)
- Surgery (AREA)
- Animal Behavior & Ethology (AREA)
- Biomedical Technology (AREA)
- Heart & Thoracic Surgery (AREA)
- Medical Informatics (AREA)
- Molecular Biology (AREA)
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Biophysics (AREA)
- Pathology (AREA)
- Physiology (AREA)
- Ophthalmology & Optometry (AREA)
- Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)
Abstract
A method of measuring a person's 2 aortic blood pressure comprises utilising a photoplethysmograph at an extremity 10 of the person in order to obtain the shape of a blood pressure pulse at the extremity 10, applying a mathematical algorithm to the shape of the blood pressure pulse at the extremity 10 in order to calculate what the shape of the aortic blood pressure pulse would be, externally measuring the person's 2 blood pressure with a sphygmomanometer 16 and using the measurement of the external blood pressure with the calculated shape of the blood pressure pulse at the heart in order to determine the pressure waveform at the person's heart and thereby to obtain the person's aortic blood pressure without invasive action.
Description
A METHOD OF MEASURING A PERSON'S
AORTIC BLOOD PRESSURE
This invention relates to a method of measuring a person's aortic blood pressure.
High blood pressure is known as hypertension and it is a major cause of cardiovascular disease and death. A person's blood pressure is usually measured externally. Typically a sphingamometer is used to measure the blood pressure such that the sphingamometer is put around a person's arm, inflated and then the brachial blood pressure is read. It is well known that it would be better to measure the person's aortic blood pressure but such a measurement of the aortic blood pressure because blood pressure in the aorta is more closely related to the load imposed on the heart.
Measurement of the aortic blood pressure rather than the brachial blood pressure may identify subjects at increased risk of cardiovascular disease.
The measurement may also identify persons with pseudo hypertension in whom brachial systolic (maximum) blood pressure is high as a result of anthropomorphic characteristics, but brachial blood pressure is normal.
Assessment of such persons using brachial blood pressure alone could lead to unnecessary treatment for the person. In spite of all this, the aortic blood A, . pressure is often not obtained because a measurement of the aortic blood I....
pressure can usually only be made in an invasive manner using a pressure catheter in the person's heart. Such measurements can only generally be made in a hospital and they are therefore not normally conducted due to lack of places and available personnel in hospitals.
US-A-5265011 discloses a method of measuring a person's aortic blood pressure in a non-invasive manner. This is effected using a tonometer in order to produce an electrical signal representative of the contours of pressure pulses in the brachial or radial arteries. The tonometer may be employed to push and deform an appropriate artery in the person, for example in the person's wrist. The part of the tonometer in contact with the artery is sensitive to pressure and there is thus obtained a pressure waveform of the radial artery. The pressure waveform is then converted to aortic blood pressure using an algorithm.
It is an aim of the present invention to provide an alternative method of non-invasively measuring a person's aortic blood pressure, which method does not use a tonometer, and which method uses an algorithm which is different from that disclosed in US-A-5265011.
Accordingly, in one non-limiting embodiment of the present invention there is provided a method of measuring a person's aortic blood pressure, which method comprises utilising a photoplesmograph at an extremity of the person in order to obtain the shape of a blood pressure pulse at the extremity, applying a mathematical algorithm to the shape of the blood pressure pulse at the extremity in order to calculate what the shape of the aortic blood pressure pulse would be, externally measuring the person's blood pressure and using the measurement of the external blood pressure with the calculated shape of the blood pressure pulse at the heart in order to determine the pressure waveform at the person's heart and thereby to obtain the person's aortic blood pressure without invasive action.
Typically, the extremity of the person is a finger tip or an ear lobe.
Other parts of the person's body may be used if desired.
Measurement of infrared light transmission through the extremity of the person gives an optical pulse. The amplitude of the optical pulse depends upon local factors such as volume and perfusion of the particular extremity of the person, for example their finger. The shape of the pulse, however, bears an approximately constant relationship to the aortic pressure waveform. By the application of an appropriate transfer function to the optical pulse, the systolic (maximum) blood pressure can be obtained providing mean arterial and diastolic blood pressure are known. The mean arterial blood pressure is known from the external measurement of the person's blood pressure.
The external measurement of the person's blood pressure is preferably obtained using a sphingamometer. Other devices for externally measuring the person's blood pressure may however be used.
The mathematical algorithm may be regarded as a transfer function which can be expressed as a parametric model in time domain or frequency domain. The transfer function could alternatively comprise a set of equations relating characteristics of the optical pulse to the aortic pulse.
The transfer function as used in conjunction with calibration factors obtained from diastolic blood pressure and mean arterial blood pressure obtained as stated above in a conventional manner.
Generally, the transfer function may comprise means for applying a scaling factor to the optically derived signal from the photoplesmograph.
The optically derived signal varies dynamically according to characteristics such as rate of change of the signal. The application of the scaling factor can be achieved by expressing the signal in the frequency domain by Fourier decomposition, applying a scaling factor to each constituent harmonic, and then re-synthesising the signal from these harmonics.
Alternatively, a parametric approach can be used in which a scaling factor is applied to each time point of the signal. The scaling factor is determined by the variation of the signal over the immediately preceding and succeeding time points.
The transfer function may be determined from simultaneous measurements of the optical pulse and aortic blood pressure measured directly by evasive means from persons undergoing cardiac catheterization.
During this procedure, a catheter is placed in the aorta, and pressure can be obtained by use of an appropriate sensor. The transfer function is optimised from data in a series of persons in whom direct measurements of systolic blood pressure have been obtained.
The apparatus may be one in which the mathematical algorithm is P(t)=a,. P(t-1)+a2.P(t-2)+...+aNa.P(t-Na) + bo.DVP (t- k) + b'.DVP (t- k -1) +...+bNb.DVP (t- k - Nb) where P is the central pressure waveform, OP is the optical waveform, t is the time variable, k is the time delay, a's and b's are the parameters of the s model, and Na and Nb are orders of the model, and in which k = 0, Na = 13 and Nb = 11.
Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows apparatus carrying out the method of the invention; Figure 2 is a block diagram of part of the apparatus shown in Figure 1; Figure 3 is a block diagram explaining how to derive aorta (central) systolic blood pressure from an optically derived pulse; Figure 4 shows three examples of optical pulses in persons of different ages; and Figure 5 shows frequency expression of an ARX model derived from persons with Na = 13 and Nb = 11.
Referring to Figure 1, there is shown a person 2 having their aortic mood pressure being measured by a person 4. The person 4 is using a measurement method comprising utilising apparatus 6 which gives a photoplesmograph. The apparatus 6 comprises a clip 8 located on a tip 10 of a finger 12 of the person 2. The photoplesmograph enables the person 4 to obtain the shape of a blood pressure pulse at the finger tip 10.
The following mathematical algorithm is applied to the shape of the blood pressure pulse at the finger tip 10 in order to calculate what the shape of the aortic blood pressure pulse would be, externally measuring the person's blood pressure using a sphingamometer 14 comprises a tube 16 which is placed around an arm 18 of the person 2. The tube 16 is inflated using a hand pump 20. The external blood pressure is shown on a dial 22.
The measurement of the external blood pressure obtained from the dial 22 is used with the calculated shape of the aortic blood pressure pulse in order to determine the pressure waveform at the person's heart and thereby to obtain the person's aortic blood pressure without invasive action.
This part of the method of the invention comprises utilising the algorithm which is stored in a computer 24, and also using a device 26.
Figure 2 illustrates how the entire apparatus comprises a signal conditioning circuit 28, a computer interface card 30, and the computer 24.
The signal conditioning circuit 28 comprises a light emitting diode (LED) driver 32, a photo diode receiver 34, and an amplifier and filter 36.
The computer interface card 30 is connected to the signal conditioning circuit 30. The computer interface card 30 comprises an analogue to digital converter 38 and a computer bus driver 40. The computer interface card 30 is connected to the computer proper 24 as shown. Also shown in Figure 2 is the finger tip 10 of the finger 12 and diodes 42, 44 in the clip 8.
Figure 3 is a block diagram explaining how to derive aortic systolic blood pressure from an optically derived pulse. As can be seen from Figure 3, measurement of pulsestyle arterial volume is first taken. Signal processing then occurs in order to reduce noise and artifact. Calibration then occurs of the volume pulses to a fixed value. Filtering then occurs with a general filter. The estimated pressure pulse is then calibrated with DBP and MAP. Determination then occurs of the maximum of the calibrated estimated pressure pulses.
Figure 4 shows optical pulses obtained from a person aged sixty years, a person aged forty five years and a person aged twenty nine years.
The transfer function used in the present invention is determined from simultaneous measurements of the optical pulse and their aortic blood pressure measured directly by invasive means and achieved from a number of subjects undergoing cardiac catheterization. As indicated above, during this procedure, a catheter is placed in the aorta, and pressure is obtained by the use of an appropriate sensor. The transfer function is optimised from data in a series of patients, in whom direct measurements of systolic blood pressure are obtained. An example of a transfer function is an ARX model in the time domain, and expressed as follows: P(t)=a'.p(t-1)+a2p(t-2)+ +aNaP(t-Na) + bo.DVP (t- k) + b'.DVP (t- k -1) +...+bNb.DVP (t- k - Nb) where P is the central pressure waveform, OF is the optical waveform, t is the time variable, k is the time delay, a's and b's are the parameters of the model, and Na and Nb are orders of the model.
From measurements of these aortic (central) pressure pulse in twenty persons, it was found that when k = 0, Na = 13 and Nb = 11, good estimates were obtained of the aortic systolic blood pressure. The transfer function is plotted in the frequency domain in Figure 5. When this transfer function was a applied to another set of persons, it could be used to estimate aortic systolic blood pressure with acceptable accuracy.
It is to be appreciated that the embodiment of the invention described above with reference to the accompanying drawings has been given by way of example only and that modifications may be effected. Thus, for example, the extremity of the person may be their earlobe instead of their finger tip.
Claims (6)
1. A method of measuring a person's aortic blood pressure, which method comprises utilising a photoplesmograph at an extremity of the person in order to obtain the shape of a blood pressure pulse at the extremity, applying a mathematical algorithm to the shape of the blood pressure pulse at the extremity in order to calculate what the shape of the aortic blood pressure pulse would be, externally measuring the person's blood pressure and using the measurement of the external blood pressure with the calculated shape of the blood pressure pulse at the heart in order to determine the pressure waveform at the person's heart and thereby to obtain the person's aortic blood pressure without invasive action.
2. A method according to claim 1 in which the extremity of the person is the finger tip or an earlobe.
3. Apparatus according to claim 1 or claim 2 in which the external measurement of the person's blood pressure is obtained using a sphingamometer.
4. Apparatus according to any one of the preceding claims in which the mathematical algorithm is a transfer function which comprises means for applying a scaling factor to an optically derived signal from the photoplesmograph.
5. Apparatus according to any one of the preceding claims in which the mathematical algorithm is an ARK model in the time domain expressed as follows: P(t)=a'P(t-1)+a2.P(t-2)+ +aNaP(t-Na) + bo.DVP (t - k) + b'.DVP (t - k - 1) +...+bNb.DVP (t- k - Nb) where P is the central pressure waveform, OP is the optical waveform, t is the time variable, k is the time delay, a's and b's are the parameters of the model, and Na and Nb are orders of the model, and in which k = 0, Na = 13 and Nb = 1 1.
6. A method of measuring a person's aortic blood pressure, substantially as herein described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0317847A GB2404439B (en) | 2003-07-30 | 2003-07-30 | A method of measuring a person's aortic blood pressure |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0317847A GB2404439B (en) | 2003-07-30 | 2003-07-30 | A method of measuring a person's aortic blood pressure |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB0317847D0 GB0317847D0 (en) | 2003-09-03 |
| GB2404439A true GB2404439A (en) | 2005-02-02 |
| GB2404439B GB2404439B (en) | 2006-03-15 |
Family
ID=27799487
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0317847A Expired - Fee Related GB2404439B (en) | 2003-07-30 | 2003-07-30 | A method of measuring a person's aortic blood pressure |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2404439B (en) |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1990011043A1 (en) * | 1989-03-24 | 1990-10-04 | Eastern Medical Testing Services, Inc. | A method and apparatus for ascertaining the contour of the pressure pulse in the central arteries from the contour of the pressure pulse in the peripheral arteries |
| US5265011A (en) * | 1989-04-03 | 1993-11-23 | Eastern Medical Testing Services, Inc. | Method for ascertaining the pressure pulse and related parameters in the ascending aorta from the contour of the pressure pulse in the peripheral arteries |
| WO1996029004A1 (en) * | 1995-03-17 | 1996-09-26 | Pwv Medical Pty. Ltd. | Non-invasive determination of aortic flow velocity waveforms |
| GB2356252A (en) * | 1999-11-12 | 2001-05-16 | Micro Medical Ltd | Determining the shape of an arterial pressure pulse in a person |
-
2003
- 2003-07-30 GB GB0317847A patent/GB2404439B/en not_active Expired - Fee Related
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1990011043A1 (en) * | 1989-03-24 | 1990-10-04 | Eastern Medical Testing Services, Inc. | A method and apparatus for ascertaining the contour of the pressure pulse in the central arteries from the contour of the pressure pulse in the peripheral arteries |
| US5265011A (en) * | 1989-04-03 | 1993-11-23 | Eastern Medical Testing Services, Inc. | Method for ascertaining the pressure pulse and related parameters in the ascending aorta from the contour of the pressure pulse in the peripheral arteries |
| WO1996029004A1 (en) * | 1995-03-17 | 1996-09-26 | Pwv Medical Pty. Ltd. | Non-invasive determination of aortic flow velocity waveforms |
| GB2356252A (en) * | 1999-11-12 | 2001-05-16 | Micro Medical Ltd | Determining the shape of an arterial pressure pulse in a person |
Also Published As
| Publication number | Publication date |
|---|---|
| GB0317847D0 (en) | 2003-09-03 |
| GB2404439B (en) | 2006-03-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20200730 |