Blood pressure:
pulse pressure
Principle
Formally it is systolic minus diastolic blood pressure. It
can be calculated by:
Pulse pressure = stroke volume/compliance (Pa
or mmHg).
Compliance is 1/elastance for a hollow organ, see Compliance (hollow
organs).
Usually, the
resting pulse pressure in healthy adults, sitting position, is about 40 mmHg.
The pulse pressure increases with exercise due to increased stroke volume and
reduced total peripheral resistance, up to pulse pressures of about 100 mmHg
while diastolic pressure remains about the same or even drops (very aerobically
athletic individuals). The latter effect further increases stroke volume and
cardiac output at a lower mean arterial pressure. The diastolic drop reflects a
much greater fall in total peripheral resistance of the muscle arterioles in
response to the exercise (a greater proportion of red versus white muscle
tissue).
Low
values
If resting pulse pressure < 40 mmHg, the most common
reason is an error of measurement. If it is genuinely low, e.g. 25 mmHg or
less, the cause may be low stroke volume, as in congestive heart Failure and/or
shock. This interpretation is reinforced if the resting heart rate is
relatively rapid, e.g. 100-120 (in normal sinus rhythm), reflecting increased
sympathetic nervous system activity.
If the usual resting pulse pressure is consistently
greater than 40 mmHg, e.g. 60 or 80 mmHg, the most likely basis is stiffness of
the major arteries, aortic regurgitation (a leak in the aortic valve), an extra
path for the blood to travel from the arteries to the veins, hyperthyroidism or
some combination. (A chronically increased stroke volume is also a technical
possibility, but very rare in practice.) Some drugs for hypertension have the
side effect of increasing resting pulse pressure irreversibly. A high resting
pulse pressure is harmful and tends to accelerate the normal ageing of body
organs, particularly the heart, the brain and kidneys.
A high pulse
pressure is an important risk factor (20% increase) for heart disease. A