Types of Blood Pressure Measurement Techniques

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.

16. Indirect Methods of Blood Pressure Measurement

17. 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 .

18. 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.

19. Automatic BP MEasurement

20. 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.

21. 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.

22. Contd..

23. 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.

24. Rheographic Method

25. 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.

26. NIBP (non-invasive blood pressure) measuring system

27. 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.

28. 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:

29. 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.

30. 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.

31. 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

32. 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.