iHealth BP5 Instructions page 11

WHAT IS MEAN ARTERIAL PRESSURE?
The Mean Blood Pressure (MAP) is the average pressure forcing blood through the ar-
teries. It is not the average of the systolic and diastolic blood pressure. It corresponds
to a state of balance between the compressive and expansive forces acting on the ar-
terial wall when there is no distension of the arterial wall, either outward or inward.
MAP is an excellent way to evaluate the stress on the walls of the vessels. It is useful
to quickly evaluate excessive load on the cardiovascular system.
The MAP is calculated as: diastolic + (0.412 x (systolic - diastolic))
WHAT IS PULSE PRESSURE?
Pulse pressure is the change in blood pressure seen during a contraction of the heart.
Formally it is the systolic pressure minus the diastolic pressure. It is calculated as: Pulse
Pressure = Systolic Pressure - Diastolic Pressure
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,
healthy values being up to pulse pressures of about 100 mmHg. In healthy individuals
the pulse pressure will typically return to normal within about 10 minutes.
If the usual resting pulse pressure is measured as less than 40 mmHg: If the pulse pres-
sure 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 high resting pulse pressure is harmful
and tends to accelerate the normal ageing of body organs, particularly the heart, the
brain and kidneys.
WHAT IS STROKE VOLUME?
The stroke volume (SV) is the volume of blood ejected from a ventricle with each beat
of the heart.
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