This content about different types of BP measurement techniques

1. BLOOD PRESSURE MEASURMENT

2. BLOOD PRESSURE
• Blood pressure is the pressure of
circulating blood against the walls of
blood vessels.
• It is measurement of the pressure of
blood inside arteries.

3. • Systolic pressure: The maximum pressure reached during
cardiac ejection is known as systolic pressure.
• Diastolic pressure: The minimum pressure occurring at the end
of ventricular relaxation is termed diastolic pressure.
• Mean arterial pressure: The mean arterial pressure over one
cardiac cycle is approximated by adding one-third of the pulse
pressure (difference between systolic and diastolic values) to
the diastolic pressure.
• Reference to atmospheric pressure: All blood pressure
measurements are made with reference to atmospheric pressure.
BLOOD PRESSURE MEASUREMENT

4. NORMAL SYSTOLIC AND DIASTOLIC PRESSURE
Normal blood pressure for most adults is
defined as a
Systolic pressure = 120 mm Hg
Diastolic pressure = 80 mm Hg

5. NORMAL RANGE
• Arterial system 30–300 mmHg
• Venous system 5–15 mmHg
• Pulmonary system 6–25 mmHg

6. METHODS OF BP MEASUREMENT
• There are two basic methods for
measuring blood pressure—
Direct method
Indirect method

7. DIRECT METHODS OF MONITORING BLOOD PRESSURE
It provides
• highest degree of accuracy
• dynamic response
• continuous monitoring
Inaccessible regions:
• Direct measurement is also employed when measuring pressure in deep
regions that cannot be accessed by indirect means.
Catheter or needle probe:
• A catheter or needle type probe is inserted through a vein or artery to
the area of interest for direct measurement.

8. DIRECT METHODS OF MONITORING BLOOD PRESSURE
• Catheter tip probe: One type of probe is the catheter tip probe,
where the sensor is mounted on the tip of the probe. Pressures
exerted on the sensor are converted into proportional electrical
signals.
• Fluid-filled catheter type: The other type is the fluid-filled
catheter, which transmits pressure through its fluid-filled
column to an external transducer. The transducer converts the
pressure to electrical signals.
• Amplification and display: The electrical signals can be
amplified, displayed, or recorded for further analysis.

9. DIRECT METHOD

10. CIRCUIT DIAGRAM FOR MEASUREMENT OF SYSTOLIC AND
DIASTOLIC PRESSURE

11. EXPLANATION
• The circuit diagram described in Figure 6.20 for processing electrical signals
from a pressure transducer includes the following components and stages:
• Transducer excitation: The pressure transducer is excited with a 5 V dc
excitation.
• Amplification stage: The electrical signals corresponding to arterial pressure
are amplified using an operational amplifier or a carrier amplifier.
• Isolated preamplifier: Modern preamplifiers used for pressure signal
processing are of the isolated type. They consist of floating and grounded
circuits similar to ECG amplifiers.
• Excitation source: The excitation for the transducer is provided by an
amplitude-controlled bridge oscillator.

12. MEASUREMENT OF SYSTOLIC PRESSURE
• Measurement of diastolic pressure: The diastolic pressure is derived
indirectly using a clamping circuit consisting of capacitor C1 and diode D1.
• Measurement of systolic pressure: A conventional peak reading voltmeter is
used to measure systolic pressure.
• Charging C3: When a positive-going pressure pulse appears at point A, diode
D3 conducts and charges capacitor C3 to the peak value of the input signal,
corresponding to the systolic value.
• Time constant selection: The time constant R3C3 is chosen to provide a
steady output to the indicating meter, allowing the systolic pressure to be
accurately measured.

13. CONTD..
• Development of clamping voltage: The clamping circuit develops a voltage
equal to the peak-to-peak value of the pulse pressure, which appears across
resistor R1.
• Charging C2: Diode D2 conducts and charges capacitor C2 to the peak value
of the pulse signal when the clamping voltage is present.
• Indication of diastolic pressure: A second meter M2 shows the difference
between the peak systolic pressure and the peak-to-peak pulse pressure
signal, indicating the diastolic pressure.
• Smoothing circuit for mean arterial pressure: If required, a smoothing circuit
can be used to read the mean arterial pressure

14. INDIRECT METHODS
Korotokoff Sounds Method or Sphygmomanometer
Auscultatory Method
Oscillometric Method
Rheographic Method

15. SPHYGMOMANOMETERS
• Method by Korotkoff: The method for determining the exact moment of artery opening
and full opening is based on the sounds produced by flow changes.
• The method, developed by Korotkoff, is commonly used in conventional
sphygmomanometers.
• Korotkoff sounds: The sounds first appear when the cuff pressure falls just below the
systolic pressure.
• They are generated by brief turbulent flow and the sharp collapse of the vessel.
• The sounds persist as the cuff pressure continues to decrease.
• The sounds disappear or change in character when the cuff pressure falls just below the
diastolic pressure, indicating uninterrupted flow.
• Sound detection: A microphone is placed over an artery distal to the cuff to pick up the
Korotkoff sounds.

17. INDIRECT METHODS OF BLOOD PRESSURE MEASUREMENT

18. 6.7.2.1 AUTOMATIC BLOOD PRESSURE MEASURING APPARATUS
USING KOROTKOFF’S METHOD
• Method of measurement: The blood pressure measurement method involves
placing a cuff around the upper part of the patient's arm and positioning a
microphone over the brachial artery.
• Cuff inflation: The cuff is inflated using a pumping system incorporated in the
apparatus. It is typically inflated to a preset pressure level well beyond the
systolic value at a rate of approximately 30 mmHg/s.
• Cuff deflation: The pressure in the cuff is then gradually decreased at a relatively
slow pace of 3-5 mmHg/s.
• Korotkoff sound detection: As air is allowed to leak from the cuff, the Korotkoff
sounds are picked up by a special piezoelectric microphone.
• Preamplification: The electrical signals from the microphone are fed into a
preamplifier to amplify the weak signals.

19. CONTD…
• Bandpass filtering: The amplified signals are then passed
through a bandpass filter with a bandwidth of 25 to 125 Hz.
This range allows for a good signal-to-noise ratio when
recording Korotkoff sounds from the brachial artery beneath
the lower edge of the cuff.
• Systolic and diastolic value determination: The system is
designed to detect the appearance of the first Korotkoff sound,
which indicates the systolic pressure. The reading on the
indicating meter is then locked. Similarly, the diastolic value
is fixed by the last Korotkoff sound.
• Cuff deflation: After the determination of the diastolic value,
the cuff is automatically and completely deflated after an
interval of 2-5 seconds.

20. AUTOMATIC BP MEASUREMENT

21. DIFFERENTIAL AUSCULTATORY TECHNIQUE
• The “differential auscultatory technique” is a non-invasive method for
accurately measuring blood pressure.
• A special cuff-mounted sensor consisting of a pair of pressure sensitive
elements, isolates the signal created each time the artery is forced open.
• As long as the cuff pressure exceeds the pressure in the artery, the artery is
held closed, and no pulse is generated.
• However, as soon as the intraarterial pressure rises to a value, which
momentarily exceeds the cuff pressure, the artery snaps” open; and a pulse is
created.
• Once the artery is open, blood flows through it giving rise to the low
frequency pressure wave signal.
• This process is repeated until the cuff pressure drops to a value below the
diastolic level.

24. OSCILLOMETRIC MEASUREMENT METHOD
• Vibrations during cuff deflation: As the occluding cuff deflates from a level
above the systolic pressure, the walls of the artery begin to vibrate or oscillate
due to turbulent blood flow in the partially occluded artery.
• These vibrations are sensed in the transducer system monitoring cuff pressure.
• Maximum oscillations and cuff pressure: As the cuff pressure further decreases,
the oscillations reach a maximum amplitude and then decrease until the cuff is
fully deflated and blood flow returns to normal.
• Correlation with blood pressure values: The cuff pressure at the point of
maximum oscillations usually corresponds to the mean arterial pressure.
• The point above the mean pressure where the oscillations rapidly increase in
amplitude correlates with the diastolic pressure.

25. CONTD..

26. DISADVANTAGES
• Sensitivity to movement or vibration:
• Excessive movement or vibration during
the measurement can lead to inaccurate
readings or failure to obtain any
reading at all.

27. RHEOGRAPHIC METHOD

28. RHEOGRAPHIC METHOD
• In this method, a set of 3 electrodes are placed in contact with the skin
Electrode B acts as a common electrode is positioned slightly distal from the midline of
the cuff.
• Electrode A and C are placed at a certain distance from the electrode B,one distally and
other proximally.
• High freqency current source of 100KHz at the input.
• The change in impedance at two points under the occluding cuff form the basis of
detection of the diastolic pressure.
• When the cuff is inflated above the systolic value, no pulse is detected by the electrode
A.
• The pulse appears when the cuff pressure is just below the systolic level.
• The appearance of the first distal arterial pulse results in an electrical signal, which
operates a valve to fix a manometer pointer on the systolic value.
• As long as the pressure in the cuff is between the systolic and diastolic values,
differential signal exists between the electrodes A and C.

29. NIBP (NON-INVASIVE BLOOD PRESSURE) MEASURING SYSTEM

30. COMPONENTS OF THE PNEUMATIC UNIT
• Air pump: A membrane-type air pump enclosed in a foam rubber-
filled casing to reduce noise.
• Damping chambers: Included in the pneumatic unit to prevent rapid
pressure increases caused by the pump, slow down pressure
changes during measurement, and smooth rapid pressure pulses
from the bleed valve.
• Safety valve: Prevents accidental cuff over-pressurization and
operates at a nominal pressure of 330 mmHg.
• Bleed valve: Controlled by pulse-width modulation, allowing for
controlled release of cuff pressure.
• Exhaust valve: Provided for quick deflation of the cuff.

31. CONTD…
• Solenoid valves: Controlled by a driver circuit
and microprocessor, responsible for controlling
the operation of the pump and valves.
• Watch dog timer: Prevents prolonged inflation
by monitoring the inflation process.
• Pressure transducer and signal processing:

32. ELECTRONIC COMPONENTS
• Piezo-resistive pressure transducer: Measures absolute pressure of the blood
pressure cuff and pressure fluctuations caused by arterial wall movement.
• Constant current source: Excites the pressure transducer.
• Differential amplifier: Amplifies the differential signal from the pressure
transducer with a gain of 30.
• Zero-control and gain control circuits: Used to calibrate and adjust the pressure
signal.
• DC channel: Measures the static or non-oscillating pressure of the cuff.
• AC component amplification: Amplifies the AC component of the pressure data
for analysis.
• High-pass filter: Blocks the DC component of the pressure signal.

33. CONTD…
• Low-pass filter: Blocks offset voltages.
• Op-amp circuit or instrumentation amplifier: Conditions the signal
from the pressure sensor.
• Analog-to-digital converter (ADC): Converts the conditioned signal
into digital form.
• Digital calculation: Systolic pressure, diastolic pressure, and pulse
rate are calculated in the digital domain using appropriate algorithms.
• LCD display: Results are displayed on a liquid crystal display.

34. MEASUREMENT OF TEMPERATURE
• The transducer commonly utilized for temperature
measurement in a patient monitoring system is a thermistor.
• Changes in temperature result in changes in resistance of the
thermistor, which are measured in a bridge circuit.
• The measured resistance values are indicated on a calibrated
meter, providing temperature readings.
• The average normal body temperature is 98.6°F or 37°C.
• Normal Range:97°F -99°F or 36.1°C- 37.2°C

35. CONTD..
• The measuring range for the temperature in a patient
monitoring system typically spans from 30°C to 42°C.
• Two channels are usually available for temperature
measurements, allowing monitoring of multiple patients or
different body regions.
• Similar to ECG monitoring, the output circuits for temperature
measurements are isolated through opto-couplers, ensuring
electrical safety and preventing interference.