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It is measured in millimeters of mercury (mmHg). It represents the force that the heart generates each time it contracts. For example, if resting blood pressure is 120/80 mmHg, then the pulse pressure is 40 mmHg.
Pulse pressure is the (higher) systolic blood pressure minus the (lower) diastolic blood pressure.
The systemic pulse pressure is approximately proportional to stroke volume, or the amount of blood ejected from the left ventricle during systole (pump action) and inversely proportional to the compliance (similar to Elasticity) of the aorta.
The aorta has the highest compliance in the arterial system due in part to a relatively greater proportion of elastin fibers versus smooth muscle and collagen. This serves the important function of damping the pulsatile (max pump pressure) output of the left ventricle, thereby reducing the initial systolic pulse pressure but slightly raising the subsequent diastolic phase (a period rather similar to Dwell time). If the aorta becomes rigid because of disorders such as arteriosclerosis or atherosclerosis, the pulse pressure would be very high because the aorta becomes less compliant due to the adhesion rigid lesions to the (otherwise flexible) aorta wall.
A pulse pressure is considered abnormally low if it is less than 25% of the systolic value. The most common cause of a low (narrow) pulse pressure is a drop in left ventricular stroke volume. In trauma, a low or narrow pulse pressure suggests significant blood loss (insufficient preload leading to reduced cardiac output).
Usually, the resting pulse pressure in healthy adults, sitting position, is about 30–40 mmHg. The pulse pressure increases with exercise due to increased stroke volume, healthy values being up to pulse pressures of about 100 mmHg, simultaneously as total peripheral resistance drops during exercise. In healthy individuals the pulse pressure will typically return to normal within about 11 minutes.
For most individuals, during aerobic exercise, the systolic pressure progressively increases while the diastolic remains about the same. In some very aerobically athletic individuals, for example distance runners, the diastolic will progressively fall as the systolic increases. This behavior facilitates a much greater increase in stroke volume and cardiac output at a lower mean arterial pressure and enables much greater aerobic capacity and physical performance. 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). Individuals with larger BMIs due to increased muscle mass (body builders) have also been shown to have lower diastolic pressures and larger pulse pressures.
If the usual resting pulse pressure is consistently greater than 100 mmHg, the most likely basis is stiffness of the major arteries, aortic regurgitation (a leak in the aortic valve), arteriovenous malformation (an extra path for blood to travel from a high pressure artery to a low pressure vein without the gradient of a capillary bed), hyperthyroidism or some combination. (A chronically increased stroke volume is also a technical possibility, but very rare in practice.) While some drugs for hypertension have the side effect of increasing resting pulse pressure irreversibly, other antihypertensive drugs, such as ACE Inhibitors, have been shown to lower pulse pressure. A high resting pulse pressure is harmful and tends to accelerate the normal aging of body organs, particularly the heart, the brain and kidneys. A high pulse pressure combined with bradycardia and an irregular breathing pattern is associated with increased intracranial pressure and should be reported to a physician immediately. This is known as Cushing's triad and can be seen in patients after head trauma related to intracranial hemorrhage or edema.
Examples: (these are examples of WIDENING pulse pressure causes)
Recent work suggests that a high pulse pressure is an important risk factor for heart disease. A meta-analysis in 2000, which combined the results of several studies of 8,000 elderly patients in all, found that a 10 mm Hg increase in pulse pressure increased the risk of major cardiovascular complications and mortality by nearly 20%. Heightened pulse pressure is also a risk factor for the development of atrial fibrillation. The authors of the meta-analysis suggest that this helps to explain the apparent increase in risk sometimes associated with low diastolic pressure, and warn that some medications for high blood pressure may actually increase the pulse pressure and the risk of heart disease.
Pulse pressure readings can be taken on a home blood pressure monitoring device. These devices display systolic and diastolic blood pressure (from which pulse pressure can be calculated) and pulse rate readings. Monitoring at home can be helpful to a medical provider in interpreting in-office results and progression of disease processes.
A 2005 study found that 5 mg of folate (Vitamin B9) daily over a three-week period reduced pulse pressure by 4.7 mm of Hg compared with a placebo, and concluded that folic acid is an effective supplement that targets large artery stiffness and may prevent isolated systolic hypertension. A longer-term (2 year) study in 158 clinically healthy siblings of patients with premature atherothrombotic disease also found an effect of folic acid (5 mg) plus pyridoxine (Vitamin B6, 250 mg) on pulse pressure, but the effect was not independent of mean arterial blood pressure, and there was no effect on common carotid artery stiffness.