MRes Bioengineering Research Project
Title of the project: Origin of the dicrotic notch in the arterial pressure waveform
Supervisor 1: Dr Jennifer Siggers
Department: Bioengineering
Imperial College campus: South Kensington
email: j.siggers@imperial.ac.uk
Supervisor 2: Prof Kim Parker
Department: Bioengineering
Imperial College campus: South Kensington
email: k.parker@imperial.ac.uk
Project Description: (up to 200 words)
Background: The arterial pressure waveform has a characteristic shape, beginning with a rapid rise
up to a maximum during systole, followed by decaying pressure during the rest of systole and
diastole. During systole, the aortic valve is open, and blood flows along the aorta away from the
heart. The dicrotic notch occurs at the end of systole. At this time the aortic valve closes, and there is
a sudden rise in pressure, normally between 5 and 10 mmHg. During diastole, the valve remains
closed, and there is no flow. The dicrotic notch resulting from the increase in aortic pressure at the
time of aortic vavle closure is important clinically because it is generally used as a marker of the end
of systole and the beginning of diastole in the cardiac cycle.
Wave intensity analysis theory follows from a simplified model of the dynamics of blood flow and
pressure in which the flow in the arteries is assumed to be one dimensional. Applying conservation
of mass and momentum over a cross section of the artery, together with a tube law, describing the
relationship between transmural pressure and cross-sectional area of the artery, leads to a system of
equations that can be solved to find the arterial pressure. It shows that information propagates
along the arteries in either direction at a characteristic wavespeed that depends on the elastic
properties of the arterial wall. This theory explains most of the features of the arterial waveform
well, and indeed it is possible to construct a network model of the arterial tree that exhibits forward
and backward waves travelling around the tree which explains the changes in the waveform that are
observed in different locations in the body.
Hypothesis: The mechanical reasons for the sudden rise in pressure at the dicrotic notch have not
been explained properly, and application of wave intensity analysis together with a rigid boundary
representing the valve does not produce realistic values of the pressure rise. Thus we hypothesise
that the valve stretches as it closes, and thus becomes a store of elastic energy. This energy is
injected into the blood after closure of the valve, leading to the observed rise in pressure.
Aims: We will develop and solve a mathematical model to predict the effect of elasticity of the valve
leaflets. The pressure rise predicted by the model will be compared with observations, which will
test the plausibility of the hypothesis.
Protocols: We will develop a simplified axisymmetric model of the valve with equations representing
the position of the valve and the stored energy in the valve during closure. These equations will act
as boundary conditions on the equations of wave intensity analysis. The equations will be solved
analytically or numerically, and the solution will lead to predictions of the valve behaviour and its
corresponding effect on pressure and flow.
Significance: Comparing the observed changes in pressure and the timescales on which they occur
will allow us to test the hypothesis. This project has the potential to explain a phenomenon that has
so far eluded our understanding. Further developments of the model could help us to understand
other phenomena such the effect of a large dicrotic pulse, an abnormal pulse associated with certain
cardiovascular conditions.
Key techniques: (please include only the names of techniques, not a description)
Mathematical modelling
Basic fluid mechanics
Wave intensity analysis applied to the cardiovascular system
Numerical programming techniques
References: (up to 3 references related to the project)
An introduction to wave intensity analysis by K H Parker (see
http://www.bg.ic.ac.uk/research/k.parker/wave_intensity_web/welcome.html)