DIFFERENT METHODS OF MEASURING BLOOD PRESSURE

Stephen Hales

• 1727- First Blood Pressure measurements by inserting glass tubes inside arteries of a Mare and recording pressure from the column of blood that rose

• Forssmann, Counard and Richard

• Nobel Prize 1956

• Procedure of cardiac catherisation

MEASURING BLOOD PRESSURE

BP MEASUREMENT

DirectIndirect

TonometricUltrasonicOscillometricAuscultatory

HybridAneroidMercury

Palpatory

Palpatory Method

• Rough Estimation of Systolic Pressure

• Carotid Femoral radial >70 mm Hg

• Carotid and Femoral > 50 mm Hg

• Carotid >40 mm Hg

Deakin CD, Low JL (September 2000). Accuracy of advanced trauma life support guidelines for predicting systolic blood pressure using carotid, femoral and radial pulses: Observational ; BMJ 321 (7262): 673–4.

Direct Method

• Direct Intra arterial Measurement of Pressure using a pressure transducer

• Systolic is recorded 5-10 mm Hg higher and Diastolic is 5-10 mm lower than non- invasive techniques

• Gold Standard• Accurate beat-to-beat monitoring

Matthew Ward, Jeremy A Langton,

Disclosures Cont Edu Anaesth Crit Care and Pain. 2007;7(4):122-126. 

Mercury Sphygmomanometer

• Samuel Siegfried Karl Ritter von Basch (1881)

• Riva Rocci (1896)

• Modern Version by Harvey Cushing (1901)

GOLD STANDARD IN CLINICAL PRACTICE

Aneroid Sphygmomanometer

• No Mercury• Metal Bellow and

Lever system• Inaccurate if not

calibrated

.Mion D, Pierin AM. How accurate are sphygmomanometers? J Hum Hypertens. 1998; 12: 245–248 Yarows SA, Qian K. Accuracy of aneroid sphygmomanometers in clinical usage: University of Michigan experience. Blood Press Monit. 2001; 6: 101–106.

Hybrid BP monitors

• Combine features of mercury and aneroid sphygmomanometers

• Mercury replaced by Electronic Pressure Gauge

• Auscultatory method used

PHYSICS OF BP MEASUREMENT

• Reynolds number

Re = ρ D v

μ

ρ- Density of the fluidD- Diameter of the vesselV- Velocity of the fluidμ- Viscosity of the fluid

Re < 2100 – Laminar flow

Re > 4000- Turbulent flow

Korotkoff SoundsPhase 1 Phase 2 Phase 3 Phase 4 Phase 5

Silence Tapping Soft Swishing

Crisp Blowing Silence

Cuff pressure

SYSTOLIC DIASTOLIC

Oscillometric Sphygmomanometer

• Records Oscillations in BP cuff

• Blood pressure determined by an algorithm

• Calibration Must

• Ambulatory and Home BP

Auscultatory Vs Oscillatory

Other Techniques

• Ultrasonic probes under cuff• Tonometry• Doppler

HOW TO MEASURE BLOOD PRESSURE IN

CLINICAL SETTING

Subject Position

• Quitely Seated atleast for 5 min in a chair• Feet on the floor• Arms at Level of Right Atrium (mid point of

sternum)• Avoid Caffeine, Exercise and Smoking 30

min prior to recording

Body Position

• Back supported

• Legs Uncrossed

• Arm supported

• Cuff at level of Right Atrium- Midpoint of the Sternum

• Arm to be at level of right atrium even when patient is supine (P=hρg)

• Support with pillow

Cuff Size

• Length: Width ratio ideally 2:1

• Tubing at least 70 cm long

Approx Size of Cuff

Length Width

Arm Circumference

Cuff Cuff Size

Upto 10 cm Newborn 4X8 cm

11-15 cm Infant 6X12 cm

16-21 cm Child 9X18 cm

22-26 cm Small Adult 12 X22 cm

27-34 cm Adult 16X30 cm

35-44 cm Large Adult 16X36 cm

45-52 cm Adult Thigh 16X 42 cm

Cuff Placement

• Midline of bladder of cuff over arterial pulsation

• Lower end 2-3 cm above cubital fossa

• Midthigh level in lower limb

Instrument at Level of Cuff

Position of Eye of Observer

• Eye at level of upper meniscus of mercury column

Inflation and Deflation

• Initial Inflation atleast 30 mm above point where radial pulse disappears

• Deflation at 2-3 mm per second• First and Last sounds to be taken as

systolic and Diastolic Pressures• Column to be read to nearest 2mm Hg

Number of Measurements

• Minimum of two readings at least intervals of atleast one min

• Average of both readings to be taken

• If diff > 5 mm Hg, more readings to be taken and averaged out

Both Arm Measurements

• Ideally, first visit should include measurement of blood pressure in both arms

• If Consistent difference in measurements without identifiable cause, higher reading should be used as baseline

Blood Pressure in Paediatric Age Group

• BP in all four limbs to be checked on first visit

• Auscultatory method satisfactory • Doppler• Oscillometric Most accurate • Palpatory method for systolic pressure • Flush method for infants – Systolic only

Self Monitoring at Home

• Useful in White Coat Hypertension• Smokers

Continuous Ambulatory BP

• White Coat Hypertension• Drug Resistance• Hypotension with Anti hypertensive

therapy• Episodic Hypertension• Autonomic Dysfunction

TAKE HOME MESSAGE

• Comfortable Sitting position of Subject• Appropriate Cuff Size• Calibrated Instrument• Proper Inflation and Deflation Procedure• Average of Readings