VOLUME 7 NUMBER 4 • NOVEMBER 2010
155
SA JOURNAL OF DIABETES & VASCULAR DISEASE
DISEASE FOCUS
change. However, during the ageing process blood vessels become more
fibrous, making them less flexible and this, in turn, affects blood pressure
and its control. As the elasticity of the blood vessels deteriorates with age,
the blood pressure steadily rises.
AUTONOMIC NERVOUS SYSTEM
The autonomic nervous system controls involuntary functions of the body
such as bladder function, digestion and bowel control, sexual function and
the cardiovascular system, including blood pressure.
The autonomic nervous system can be divided into two: the sympa-
thetic and parasympathetic systems. The two systems work together to
balance and control the involuntary functions of the body. Broadly speak-
ing, stressful situations require more sympathetic action, so increase the
cardiac output, pulse rate and blood pressure. Periods of rest, relaxation
and stability have more input from the parasympathetic nervous system.
For example, when someone is sleeping, cardiac output, pulse rate and
blood pressure are all lower than when awake.
Most organs in the body have sympathetic and parasympathetic ac-
tions, although most blood vessels have no parasympathetic input, and
rely on the amount of sympathetic action to control constriction and dila-
tation of the blood vessel. However, the parasympathetic nervous system
influences the rate and force of the heartbeat, which, in turn, influences
blood pressure. In this way, the two systems work together to fine-tune
blood pressure depending on the body’s needs. Activity levels, patient
wellbeing, age and gender all influence this.
DIABETES AND NEUROPATHY
Autonomic neuropathy occurs when the autonomic neurons of the sym-
pathetic and parasympathetic nervous systems become damaged. Au-
tonomic neuropathy caused by diabetes is, unfortunately, very common,
with an estimated 50% of people with diabetes having it in some form.
Many patients are symptomatic but some people are not and so will be
unaware that they have neuropathy.
Neuropathy is more common in patients who have had diabetes for a
long time, and in those whose glucose control is suboptimal. Good control
of blood glucose, cholesterol, blood pressure and body weight minimises
the risks and progression of the nerve damage that causes neuropathy.
The precise mechanism and cause of diabetic neuropathy are not fully
understood.
Common symptoms of autonomic neuropathy include changes in di-
gestion, bowel and bladder control. Loss of sexual function, excessive
perspiration, postural hypotension and loss of sensation in the hands and
feet are also common problems.
THE CARDIOVASCULAR SYSTEM AND NEUROPATHY
Damage to the nerves in the cardiovascular system can lead to problems
with blood pressure control. The effect of this is to cause a significant
drop in blood pressure after sitting or resting or following long periods of
standing. Typically, the patient feels light-headed and faint. This is known
as postural hypotension.
Hypovolaemia caused by the over-use of diuretics or vasodilators, as
well as dehydration, can also cause postural hypotension. Dehydration
can occur due to inadequate fluid intake or excessive alcohol consump-
tion, or a combination of the two.
POSTURAL HYPOTENSION
On standing up, gravity encourages the blood in the legs to pool and stag-
nate rather than continuing to circulate towards the heart and lungs. The
autonomic nervous system prevents this pooling by contracting the veins
in the legs to aid venous return and maintain adequate blood supply to
the brain. Damage to the autonomic nervous system inhibits this process,
leading to postural hypotension. Checking blood pressure when standing
and sitting can help to identify any potential problems.
Postural hypotension is defined as a reduction in systolic blood pres-
sure of 20 mmHg or more after standing for at least one minute, or a di-
astolic drop of 10 mmHg or more three minutes after standing. To put this
into context, hypertension is blood pressure sustained at 140/85 mmHg
or above, and hypotension is blood pressure persistently less than 90/60
mmHg. Not every diabetic with postural hypotension will have symptoms.
Given that blood pressure varies according to activity levels and pos-
ture, a person sitting would be expected to have lower blood pressure
than when standing. However, it is the difference between the two record-
ings that is significant. Routinely checking a patient’s blood pressure while
sitting and standing and comparing the two readings is good practice and
alerts staff to any potential issues before the patient suffers any symp-
toms.
TREATMENT AND MANAGEMENT
A review of the patient’s medication is pertinent, particularly looking at
diuretics and vasodilators used for blood pressure control. This should be
done at the same time as regular blood pressure recordings to ensure that
the patient’s blood pressure remains within recommended targets while
minimising symptoms.
The patient should be advised to sit and stand more slowly to avoid
sudden changes in blood pressure, making unpleasant symptoms less
likely. Advice about adequate fluid intake and avoiding excess alcohol to
minimise possible dehydration and hypovolaemia should be explained.
There are specific drugs available to treat postural hypotension but
consideration of current medication and the patient’s lifestyle are often
all that is needed. Blood glucose control and cholesterol levels should be
reassessed and appropriate action taken if required. The patient should be
given clear explanations, so that they can understand what is happening
and why, and how they can prevent further progression and symptoms.
Preventing neuropathy and postural hypotension
•
Good control of blood glucose
•
Maintaining target cholesterol levels
•
Optimal blood pressure control
•
Losing weight if overweight or obese
