Case Five: Guard Your Heart

Case Five: Guard Your Heart CARDIOVASCULAR SYSTEM

REGULATION OF ARTERIAL BLOOD PRESSURE

Blood pressure - the force exerted by the blood against any unit area of the vessel wall.

When one says that pressure in a vessel is fifty millimeters of mercury, one means that the force exerted is sufficient to push a column of mercury against gravity up to a level fifty millimeters high.

Systolic pressure - is the highest arterial pressure during a cardiac cycle.

This occurs when the heart contracts and blood is ejected into the arterial system.

Diastolic pressure - is the lowest arterial pressure during a cardiac cycle.

This occurs when the heart is relaxed and blood is being returned to the heart via the veins.

Mean arterial pressure - The mean arterial pressure is the average of the arterial pressures measured millisecond by millisecond over a period of time.

It is not equal to the average of the systolic and diastolic pressures because at normal heart rates, a greater fraction of the cardiac cycle is spent in diastole than in systole. Thus, the arterial pressure remains closer to diastolic pressure than to systolic pressure during the greater part of the cardiac cycle.

At the usual heart rate, the mean arterial pressure is determined about sixty percent by the diastolic pressure and forty percent by the systolic pressure.

Mean Arterial Pressure equals Diastolic Pressure plus

MAP equals Diastolic Pressure plus three

(Systolic Pressure minus Diastolic Pressure) divided by three

Diastolic Pressure plus Systolic Pressure

Nearer the diastolic pressure than to the systolic pressure during the greater part of the cardiac cycle.

Pulse pressure - is the difference between systolic and diastolic pressures, which is about forty millimeters of mercury.

Factors that affect pulse pressure:

One. The stroke volume output of the heart

Two. The compliance (total distensibility) of the arterial tree

Three. The character of ejection from the heart during systole.

The first two are major factors while the third is a less important factor.

However, the most important determinant of pulse pressure is stroke volume.

As blood is ejected from the left ventricle into the arterial system, systolic pressure increases dramatically because of the relatively low capacitance of the arteries.

Since diastolic pressure remains unchanged during ventricular systole, the pulse pressure increases to the same extent as does systolic pressure.

Decreases in capacitance, such as those that occur with the aging process, cause the pulse pressure to increase.