- is pulsatile.
- is not constant during a cardiac cycle.
> Pulse pressure
Figure 3-2. Arterial pressure during the cardiac cycle.
1. Systolic pressure
- is the highest arterial pressure during a cardiac cycle.
- is measured after the heart contracts (systole) and blood is ejected into the arterial system.
2. Diastolic pressure
- is the lowest arterial pressure during a cardiac cycle.
- is measured when the heart is relaxed (diastole) and blood is returning to the heart via the veins.
3. Pulse pressure
- is the difference between the systolic and diastolic pressures.
-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 because of the relatively low capacitance of the arteries. Because 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 increases in pulse pressure.
4. Mean arterial pressure
- is the average arterial pressure with respect to time.
- can be calculated approximately as diastolic pressure plus one-third of pulse pressure.
H. Venous pressure
- The veins have a high capacitance and, therefore, can hold large volumes of blood at low pressure.
I. Atrial pressure
- is even lower than venous pressure.
- Left atrial pressure is estimated by the pulmonary wedge pressure. A catheter, inserted into the smallest branches of the pulmonary artery, makes almost direct contact with the pulmonary capillaries. The measured pulmonary capillary pressure is slightly higher than the left atrial pressure.
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