Measurement of blood pressure

[Ref: KB Primary course May 2005]

Indirect (noninvasive)

Riv-Rocci cuff

• Cuff inflated and deflated to various pressures
• Various methods are used to detect distal blood flow
  * e.g. palpation, Korotkoff sounds, pulse monitor, ultrasound

Penaz method

• Used on finger
• Combination of pressure cuff with infrared transmitter/sensor.
• As part of initial calibration, the apparatus automatically acquires mean BP from the point of maximum oscillation
• Afterwards, cuff pressure is automatically electronically adjusted to keep the blood volume (as detected by IR sensor) constant.

Direct (invasive)

Advantages include

• Immediate
• Accurate
• Continuous
• Reliable

Disadvantages include

• Possible infection
• Possible thrombosis
• Possilbe pneumothorax, haemothorax, hydrothorax
• Damage to arteries
• More costly
• Need to technical skills

A. Catheter tip transducer

Diaphragm directly exposed to blood flow

• Advantage: highly accurate (due to extremely high resonant frequency e.g. 20,000Hz)
• Disadvantage: Expensive, delicate

e.g. Camino ICP monitor

B. Catheter-transducer system

Transducer is coupled to the circulation via a fluid-filled catheter

• Disadvantage: inaccurate recording of SBP and DBP due to low dynamic response