Question 11.1
The following set of questions relate to invasive arterial blood pressure monitoring.
11.1. The above series of figures represents waveforms obtained simultaneously from different arterial sites from the same patient.
Assuming optimal dynamic responses, list the likely sites A-E.
College Answer
A- central aorta
B- proximal UL
C- Distal UL or LL
D- Proximal LL
E- Distal UL or LL
Discussion
Normal arterial line waveform variations are discussed in greater detail elsewhere.
In brief:
The further you get from the aorta,
- The taller the systolic peak (i.e. a higher systolic pressure)
- The further the dicrotic notch
- The lower the end-diastolic pressure (i.e. the wider the pulse pressure)
- The later the arrival of the pulse (its 60msec delayed in the radial artery)
But, the MAP doesn't change very much.
This is because, from the aorta to the radial artery, there is little change in the resistance to flow.
MAP only really begins to change once you hit the arterioles.
This is called Distal systolic pulse amplification:
The systolic peak is steeper the further down the arterial tree you travel because of “reflected waves”.
References
Moxham, I. M. "Physics of invasive blood pressure monitoring." Southern African Journal of Anaesthesia and Analgesia 9.1 (2003): 33-38.
Jonathan B. Mark's Atlas of Cardiovascular Monitoring.
Leslie Geddes' Handbook of Blood Pressure Measurement (1991),