Classifications

• • 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 for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
  • A61B5/021—Measuring pressure in heart or blood vessels
  • A61B5/02108—Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics
  • A61B5/02125—Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics of pulse wave propagation time
• • 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 for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
  • 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
• • 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 for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
  • A61B5/024—Measuring pulse rate or heart rate
  • A61B5/0245—Measuring pulse rate or heart rate by using sensing means generating electric signals, i.e. ECG signals
• • 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 for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
  • A61B5/026—Measuring blood flow
  • A61B5/0285—Measuring or recording phase velocity of blood waves
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
  • A61B5/316—Modalities, i.e. specific diagnostic methods
  • A61B5/318—Heart-related electrical modalities, e.g. electrocardiography [ECG]
  • A61B5/346—Analysis of electrocardiograms
  • A61B5/349—Detecting specific parameters of the electrocardiograph cycle
  • A61B5/352—Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval

Definitions

• This -invention relates to a method and apparatus for the determination of arterial blood pressure.
• determination of the time interval between a heart beat and the associated arterial pulse is related, inter alia, to arterial blood pressure and hence may be used to provide a continuous, non-invasive method for the determination of arterial blood pressure.
• the non-invasive method uses a sphygmomanometer which comprises an inflatable rubber cuff connected to a mercury manometer.
• the cuff is placed around the upper arm and inflated until blood flow in the brachial artery is occluded.
• a stethoscope is then used, as the pressure in the cuff is gradually reduced, to determine the systolic and diastolic measuring points. The pressure of each of these points is read from the manometer and quoted as the blood pressure.
• the technique is simple to operate and firmly established in general and clinical medical practice but is not particularly accurate and, since each measuring operation takes some 20-30 seconds to perform, is discontinuous.
• a method for the measurement of arterial blood pressure comprises sensing a heart beat, sensing an arterial pulse at at least one location and ascertaining the time interval between at least one heart beat and at least one associated arterial pulse.
• the invention also includes apparatus for the measurement of arterial blood pressure, the apparatus comprising first sensing means for sensing a heart beat, second sensing means for sensing an arterial pulse at at least one location, and means for ascertaining the time interval between at least one heart beat and at least one associated arterial pulse.
• the present invention therefore, provides a continuous, non—invasive technique and the output of the apparatus according to the invention is representative, inter alia, either of dynamic comparative blood pressure or, with suitable calibration, dynamic absolute blood pressure.
• the heart beat sensing means may comprise a simple pressure transducer in contact with the chest but it is preferred for reasons of accuracy to utilise electrocardiography.
• electrocardiography we have found that the R wave of an electrocardiogram, which corresponds to the beginning of ventricular systole, is a convenient reference for measurement of cardioarterial dela .
• the arterial pulse may be sensed at one or more locations, for example at the carotid or temporal arteries in the head and neck, at the brachial radial or ulnar arteries in the arm and wrist, and/or in the fingertip, groin and leg.
• Sensors which may be used include temperature sensitive devices, piezo-electric transducers, strain gauges, ultrasonic transducers and plethys ographic transducers.
• Ultrasonic transducers rely on the Doppler effect to detect movement in the arterial wall and/or the flow of blood corpuscles while plethysmographic transducers measure volume changes which result from arterial pulsatile blood flow.
• Volume changes may be detected by measurement of impedance changes or temperature changes but we prefer to use - ⁇ - photoplethysmography, which is an optical technique.
• photoplethysmography light is transmitted into the tissues and the amount of light reflected is inversely proportional to the volume of blood present in the artery, thereby affording a means of detecting changes in volume of the artery with pulse.
• light in the near infra-red region (wavelength 700- lOOOnm) is used since such light has a relatively high transmittance through tissue but is scattered by blood.
• ⁇ light emitting diode which emits in the infra-red may be used as the source of light and a light-sensitive photo-transistor may be used to measure reflected light.
• An infra-red light emitting diode is particularly convenient because the degree of scattering of light of this wavelength is substantially Independent of the degree of oxygenation of the blood.
• the time interval between heartbeats and associated arterial pulses may be ascertained using either an analogue or a digital approach.
• the time intervals are electronically processed to give information such as average and instantaneous values of blood pressure and/or to cause operative reactions in other equipment of a diagnostic or therapeutic nature, such as warning devices and the like.
• Fig. 1 is a block diagram illustrating the equipment and procedures to which subjects were subjected to determine a delay (Td) between heart beats and associated arterial pulses;
• Fig. 2 is a block diagram showing an electrocardiograph system
• Fig. 3 is a block diagram showning an arterial pulse transducer system
• Figs. 4.1 to 4.7 are plots of Td against average blood pressure for each of seven subjects.
• a subject under test was connected as shown to an electrocardiograph and to an arterial pulse transducer.
• a standard application of bipolar recording was used in which three identical electrodes are attached one to each arm and one to the left leg of the subject. The two arm electrodes were conncted to the inputs of a differential amplifier, the leg one being connected to common.
• the differential output was fed to a band pass filter with an approximate 3dB bandwidth of 0.08-80 Hz. This filter was used to remove noise and unrelated spurious signals.
• the output of the band pass filter was fed to a 50 Hz notch filter. This provided some 20dB's of attenuation at 50 Hz.
• the output of the notch filter was differentiated for convenience to provide a signal based on the rate of change of the ECG.
• the ZERO crossings of the derived waveform indicate the peaks of the original ECG waveform.
• the arterial pulse transducer comprised a Texas Instruments' TIL 139 combined gallium arsenide IR-emitting diode/npn silicon phototransistor mounted together in a moulded ABS plastics housing and held against the finger to detect the arterial pulse therein.
• the emission from this device typically peaks at wavelength of 940nm. At this wavelength, variations in the optical density of the underlying tissue are primarily determined by the pressure pulse.
• the output of the phototransistor was amplified and fed to a band pass filter and a notch filter similar to those described with reference to Fig. 2. The notch filter output was then fed via a variable non-inverting amplifier to a differentiating circuit identical to that used for the electrocardiograph signal.
• ECG electrocardiograph
• AP arterial pulse
• the subject under test was connected to the equipment as shown in Fig. 1.
• the arterial pulse signals were obtained by using the AP transducer to detect the subject's finger pulsations.
• the experiment was divided into three parts: i. Initially measurements were made of the systolic and diastolic arterial blood .pressure with the subject "at rest", using a sphygmomanometer . ii. A period of exercise was undertaken consisting of a short jogging session around a predetermined route, sufficient to raise the subject's blood pressure to a high value. iii. Periodic measurements of systolic and diastolic blood pressure were then made until the subject's blood pressure had returned to the "at rest" value measured in (i).
• the ECG and AP results were recorded simultaneously with the blood pressure measurements being taken.
• the Medelec UV recorder used for the differentiated outputs is an instrument consisting of both an oscilloscope and UV trace recorder. Traces displayed on the oscilloscope screen can also be recorded on UV sensitive paper producing a permanent record of the waveform being displayed.
• the oscilloscope has four inputs, two of which are connected to ECG and AP differentiator outputs. The other two are calibrated to ground and positioned to be superimposed on the AP and ECG traces to provide a reference. This ground reference is used to determine the zero crossing that defines the peaks of the input waveforms.
• a set of average Td values and a set of average blood pressure values measured manually by sphygmomanometer were derived.
• sets of 7 or 8 values were obtained.

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• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Cardiology (AREA)
• Engineering & Computer Science (AREA)
• Heart & Thoracic Surgery (AREA)
• Surgery (AREA)
• Veterinary Medicine (AREA)
• Biophysics (AREA)
• Pathology (AREA)
• Biomedical Technology (AREA)
• Public Health (AREA)
• Medical Informatics (AREA)
• Molecular Biology (AREA)
• Physics & Mathematics (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Physiology (AREA)
• Vascular Medicine (AREA)
• Hematology (AREA)
• Signal Processing (AREA)
• Ophthalmology & Optometry (AREA)
• Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)

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• 1984
  • 1984-01-20 GB GB848401500A patent/GB8401500D0/en active Pending
• 1985
  • 1985-01-21 WO PCT/GB1985/000030 patent/WO1985003211A1/en not_active Ceased
  • 1985-01-21 EP EP85900704A patent/EP0168461A1/de not_active Withdrawn

Non-Patent Citations (1)

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