Effects of physiological induced changes in afterload of the left ventricle on the strain-volume loop

Both acute and chronic changes of the preload and afterload of the heart
influence the heamodynamics, structure and function of the ventricles. In case
of as well acute as chronic changes of the loading condition of the ventricle
wall, the ventricle tries to correct the changed loading condition by changing
it's function (contractility) or structure (wall thickness or dilatation) of
the ventricle wall.
Introduction of speckle tracking echocardiography allows measurement of the
ventricular deformation (i.e. strain). By combining temporal echocardiographic
measurements of strain (functional) and volume (structure) of the left
ventricle a strain-volume loop can be constructed. Using this strain-volume
loop allows us to detect changes in heamodynamic conditions of the ventricles.
In a previous study we found that chronic changes in afterload result in
changes in the strain-volume loop. To further assess the usability of this new
technique we aim to assess the effects of acute changes in afterload on the
strain-volume loop, by increasing as well as decreasing the afterload of the
heart.
In addition to this we know that strain is influenced by increasing age,
therefore we also will assess the influence of age on the observed changes in
the strain-volume loop to determine whether age influences the applicability of
this technique.

Our primary aim is to determine whether the changes of the strain-volume loop
can be used to detect an acute change of the afterload (and thus heamodynamics)
of the heart in healthy subjects.

Our secondary aim is to determine whether age influences the observed changes
of the strain-volume loop.

In this exploratory study, 40 healthy subjects will be assessed prior to and
after an intervention through a non-invasive echocardiographic assessment

To induce the changes in afterload we will use two different interventions:
- To reduce the afterload (and preload) we will use vasodilative medication
(vasodilator; nitroglycerine), which will primary reduce the peripheral
vascular resistance.
- To increase the afterload we will use anti gravity jeans to occlude the blood
supply of the legs for 2 minutes (transient atrial occlusion), which will cause
a increase in the peripheral vascular resistance.

During this study, subjects are scheduled to visit the department of physiology
only once. During the measurements a echocardiographic assessment will be
preformed prior to and during a stimulus which increases (anti gravity jeans)
or decreases (nitrogycerine) the afterload. All measurements are non-invasive
and without any added risks for the subject. The risks of both interventions
(the antigravity jeans, and a low dose of sublingual administered
nitroglycerine) are negligible.