Pressure Measurement

Grossman’s cardiac catheterization, angiography, and intervention

CV R5 許志新醫師Supervisor: 趙庭興醫師

Pressure Wave

• Complex periodic fluctuation in force per unit area

Pressure Measuring Devices

Sensitivity

• The ratio of the amplitude of the recorded signal to the amplitude of the input signal

• More rigid the sensing membrane,the lower the sensitivity

Frequency Response

• The ratio of output amplitude to input amplitude over a range of frequencies of the input pressure wave

• The range of good frequency response is improved by stiffening the membrane

Natural Frequency and Damping

• Any means of dissipating the energy of this oscillation, such as friction, is called damping.

• Optimal damping dissipates the energy gradually, thereby maintaining the frequency response curve nearly flat .

• Damping helps to prevent over-shoot artifacts resulting from resonance of the system,but diminished frequency response

What Frequency Response is Desirable

• The useful frequency response range of commonly used pressure measurement system is usually less than 20 Hz

• The natural frequency is directly proportional to the lumen radius of the catheter system and inversely to the length of the catheter

The Electrical Gauge

• Pressure measurement systems today generally use electrical strain gauges and employ the principle of the Wheatstone bridge.

Practical Pressure Transducer System for the Catheterization

Laboratory

Zero Level

• The zero level should be positional approximately 5 cm below the left sternal border at the fourth left intercostal space.

• Each case should measure AP diameter at the level of the angle of Louis

Physiologic Caracteristics of Pressure Waveforms

• Reflected waves

• Wedge pressure

Reflected Waves

Wedge Pressures

• A true wedge pressure can be measured only in the absence flow

Sources of Error and Artifact

• Deterioration in frequency response

• Catheter impact artifact

• systolic pressure amplification in the periphery

• Errors in zero level, balancing, or calibration

Deterioration in Frequency Response

• Air bubbles: excessive damping and lower the natural frequency

Catheter Whip Artifact

• Catheter whip artifacts may produce superimposed waves of ± 10mmHg

End-pressure Artifact

• Flowing blood has a kinetic energy

• Flow suddenly come to a halt, the kinetic energy is converted in part into pressure

• 2-10 mmHg

Catheter Impact Artifact

• Catheter impact artifact are common with pigtail catheter in the left ventricular chamber, where terminal pigtail may be hit by the mitral valve leaflets as they open in early diastole

Systolic Pressure Amplification in the Periphery

• This phenomenon may mask and distort pressure gradients across the aortic valve or left ventricular outflow tract.

• Double-lumen pigtail

• Second catheter

• Carefully pullback

Errors on Zero Level,Balancing, or Calibration

• Tracking down an unexpected pressure gradient, flushing of the zero line is an important initial step.

• If the unexpected gradient persists, catheter attachments should be switched between the two involved manifolds