Abstract

Introduction This article is a descriptive report of a novel way of demonstrating the
cardiovascular response to progressive haemorrhage using simulation.
The aim of the simulated haemorrhage is to improve the understanding of the
cardiovascular response to haemorrhage and demonstrate ‘live’ the body’s response to
reduced venous return.
Method Phase 1 of a ‘simple’ haemorrhage is simulated in 6 medical students by
applying sub-atmospheric pressure to the lower body using a lower body negative
pressure (LBNP) chamber. The sub-atmospheric pressure causes ‘pooling’ of blood in
the vessels of the legs and pelvis, which reduces venous return thus mimicking the
effects of haemorrhage. Parts of this method have been described elsewhere (1). A
range of cardiovascular parameters are monitored throughout the demonstration to
allow students to observe the integrated response to ‘progressive haemorrhage’. Stroke
volume is monitored using a portable ultrasound machine, heart rate is measured from
an ECG trace and blood pressure using an automated sphygmomanometer. Skeletal
muscle and brain oxygenation, which in this context reflects changes in blood flow, is
assessed using Near Infrared Spectroscopy (NIRS).
Results Simulated haemorrhage reduces venous return, thus reducing stroke volume
by Starling’s law of the heart (2) and ultimately reduces arterial pulse pressure. The
body’s initial response (mediated by the baroreceptor reflex) to this is an increase in
heart rate to maintain mean blood pressure (3) in the face of a falling cardiac output.
The students also calculate the changes in total peripheral resistance and are able to see
the consequences for brain and skeletal muscle oxygenation.
Conclusion Durham University Medical Programme uses simulation in a novel way to
reinforce didactic teaching of the cardiovascular response to haemorrhage utilising a
LBNP chamber.