154
VOLUME 7 NUMBER 4 • NOVEMBER 2010
SA JOURNAL OF DIABETES & VASCULAR DISEASE
POSTURAL HYPOTENSION
Disease Focus
A
s we aim for tighter and tighter blood pressure control to minimise the cardiovascular com-
plications of diabetes, the risk of postural hypotension increases. In this article we discuss
what postural hypotension is and how to identify it and confirm diagnosis. We also consider
the main causes and the relationship between diabetic neuropathy and postural hypotension as
well as prevention and treatment strategies.
Sandra Waddingham
Diabetes Co-ordinator
North Lancs PCT
Blood pressure is the force of blood exerted on the
walls of the arteries as the heart contracts and relaxes.
The highest pressure is the systolic pressure, which is
exerted when the heart contracts and pushes blood
out of the left ventricle and through into the arteries.
When the heart relaxes between beats, the pressure
is lower in the blood vessels and this is the diastolic
blood pressure.
Blood pressure is measured in millimetres of mer-
cury (mmHg) and the difference between the systolic
and diastolic pressures is the pulse pressure. The
purpose of arterial blood pressure is to enable sub-
stances such as nutrients, hormones and enzymes to
move around the body and in and out of the organs, to
enable the body to function and maintain homeostasis.
BLOOD PRESSURE IS VARIABLE
The blood pressure of an individual varies, depending
on the time of day, type of activity, whether the person
is sitting or standing, and gender and age. It is lower
at night, when in bed. This means that it is perfectly
normal for the systolic, diastolic and pulse pressures
to vary during the course of a day. Blood pressure in-
creases with age and is generally higher in women
than men.
Cardiac output and peripheral resistance also affect
blood pressure. Cardiac output is the volume of blood
pushed out of the left ventricle and is expressed in
litres per minute. Stroke volume is the amount of blood
leaving the left ventricle with each heartbeat. This is
clearly influenced by the amount of blood returning to
the heart via the inferior and superior venae cavae.
The amount of blood pumped out of the heart into
the aorta multiplied by the number of beats per minute
will give the cardiac output. The higher the volume of
blood leaving the heart, the higher the cardiac output,
and the higher both the systolic and diastolic pres-
sures are likely to be.
Peripheral resistance is determined by the vaso-
constriction and vasodilatation that takes place in the
arterioles, which are the smallest arteries. Vasocon-
striction increases blood pressure, while vasodilata-
tion reduces it. Most blood vessels have a sympathetic
nerve supply to the muscle but not a parasympathetic
supply, so dilatation and constriction of the vessels are
controlled by the amount of sympathetic nerve stimu-
lation.
Healthy young blood vessels are composed of flex-
ible elastic tissue, making them very responsive to
Key points
•
Blood pressure increases with age
•
The autonomic nervous system is
responsible for controlling blood
pressure
•
Blood pressure varies throughout
the day
•
Neuropathy caused by diabetes is
very common and can be responsi-
ble for postural hypotension
•
Postural hypotension is a signifi-
cant reduction in blood pressure
that occurs between sitting and
standing
•
Postural hypotension is likely to
be more common as we aim for
tighter and tighter blood pressure
control
S Afr J Diabetes Vasc Dis 2010;
7
: 154–155.
