Invasive arterial blood-pressure monitoring

Regarding invasive arterial blood pressure monitoring, which one of the following

statements is TRUE?

a) An overdamped waveform underestimates diastolic pressure

b) An anacrotic notch is a sign of severe aortic stenosis

c) A rapid systolic upstroke is associated with a high systemic vascular resistance

d) The dicrotic notch appears later in the waveform complex if measured at the radial

artery compared to the dorsalis pedis

e) Critical damping refers to the perfect level of damping and is the desired set-up for

the system

Answer: b

Explanation

An overdamped waveform underestimates systolic pressure and overestimates diastolic

pressure. The opposite is the case for an underdamped waveform. An anacrotic

notch is a sudden fall on the upstroke of the arterial waveform and is seen in severe

aortic stenosis limiting the upstroke. A slow systolic upstroke is associated with a high

systemic vascular resistance or poor myocardial contractility. The waveform changes

morphology the further it travels away from the heart with the dicrotic notch appearing

later in the complex. Optimal damping in the context of arterial lines refers to the

perfect level of damping and is the desired set-up for the system. Critical damping (a

damping coefficient of 1.0) is when deflection returns as quickly as possible to the null

point without any overshoot. However, a critically damped system would have a slow

response time and may not show maximal amplitude. Optimal damping (damping

coefficient 0.69 or thereabouts) is a compromise between underdamping and overdamping.

Underdamping allows some degree of overshoot in order to maximise

response time and allows accurate display of magnitude. Overdamping keeps resonance

to a minimum.