Pulse pressure

Pulse pressure is the difference between systolic and diastolic blood pressure. It is measured in millimeters of mercury (mmHg). It represents the force that the heart generates each time it contracts. Healthy pulse pressure is around 40 mmHg. A pulse pressure that is consistently 60 mmHg or greater is likely to be associated with disease, and a pulse pressure of 50 mmHg or more increases the risk of cardiovascular disease. Pulse pressure is considered low if it is less than 25% of the systolic. (For example, if the systolic pressure is 120 mmHg, then the pulse pressure would be considered low if it is less than 30 mmHg, since 30 is 25% of 120.) A very low pulse pressure can be a symptom of disorders such as congestive heart failure.
Calculation
Pulse pressure is calculated as the difference between the systolic blood pressure and the 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 to dampen the pulsatile (maximum pumping pressure) of the left ventricle, thereby reducing the initial systolic pulse pressure, but slightly raising the subsequent diastolic phase. If the aorta becomes rigid because of disorders, such as arteriosclerosis or atherosclerosis, the pulse pressure would be high due to less compliance of the aorta.
Systemic pulse pressure (usually measured at upper arm artery) = Psystolic - Pdiastolic
e.g. normal 120mmHg - 80mmHg = 40mmHg
low: 107mmHg - 80mmHg = 27mmHg
high: 160mmHg - 80mmHg = 80mmHg
Pulmonary pulse pressure is normally much lower than systemic blood pressure due to the higher compliance of the pulmonary system compared to the arterial circulation. It is measured by right heart catheterization or may be estimated by transthoracic echocardiography Normal pulmonary artery pressure is between 8mmHg -20 mm Hg at rest.
e.g. normal: 15mmHg - 8mmHg = 7mmHg
high: 25mmHg - 10mmHg = 15mmHg
Values and variation
Low (narrow) pulse pressure
A pulse pressure is considered abnormally low if it is less than 25% of the systolic value. If the pulse pressure is extremely low, i.e. 25 mmHg or less, it may indicate low stroke volume, as in congestive heart failure.
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.
A narrow pulse pressure is also caused by aortic stenosis. This is due to the decreased stroke volume in aortic stenosis. Other conditions that can cause a narrow pulse pressure include blood loss (due to decreased blood volume), and cardiac tamponade (due to decreased filling time). In the majority of these conditions, systolic pressure decreases, while diastolic pressure remains normal, leading to a narrow pulse pressure.
High (wide) pulse pressure
From exercise
For most individuals, during aerobic exercise, the systolic pressure progressively increases while the diastolic pressure remains about the same, thereby widening the pulse pressure. These pressure changes facilitate an increase in stroke volume and cardiac output at a lower mean arterial pressure, enabling greater aerobic capacity and physical performance. The diastolic drop reflects a reduced systemic vascular resistance of the muscle arterioles in response to the exercise.
Consistently high
A pulse pressures of 50 mmHg or more can increase the risk of heart disease, heart rhythm disorders, stroke and other cardiovascular diseases and events. Higher pulse pressures are also thought to play a role in eye and kidney damage from diseases such as diabetes.
Conditions that can lead to a high pulse pressure include aortic regurgitation, aortic sclerosis, severe iron-deficiency anemia (due to decreased blood viscosity), arteriosclerosis (due to loss of arterial compliance), and hyperthyroidism (due to increased systolic pressure). In aortic regurgitation, the aortic valve insufficiency results in the backward flow of blood (regurgitation) that is ejected during systole, and its return to the left ventricle of the aorta during diastole. This increases the systolic blood pressure, and decreases the diastolic blood pressure, leading to a widened pulse pressure.
If the usual resting pulse pressure is consistently greater than 100 mmHg, potential factors are stiffness of the major arteries, aortic regurgitation (a leak in the aortic valve), or arteriovenous malformation, among others.
While some drugs for hypertension have the side effect of increasing resting pulse pressure, other antihypertensive drugs, such as hydrochlorothiazide, have been shown to lower pulse pressure. A high pulse pressure combined with bradycardia and an irregular breathing pattern is associated with increased intracranial pressure, a condition called Cushing's triad seen in people after head trauma with increased intracranial pressure.
Common causes of widening pulse pressure include:
Anemia
Aortic dissection
Atherosclerosis
Arteriovenous fistula
Chronic aortic regurgitation
Aortic root aneurysm
Aortic root dilation
Beri beri
Distributive shock
Endocarditis
Fever
Heart block
Increased intracranial pressure
Patent ductus arteriosus
Pregnancy
Thyrotoxicosis
Clinical significance
A vast amount of diagnostic, prognostic, and prophylactic value can be derived from the proper monitoring and interpretation of pulse pressure. Pulse pressure has implications for both cardiovascular disease as well as many non-cardiovascular diseases.
Cardiovascular disease and pulse pressure
Awareness of the effects of pulse pressure on morbidity and mortality is lacking relative to the awareness of the effects of elevated systolic and diastolic blood pressure. However, pulse pressure has usually been found to be a stronger independent predictor of cardiovascular events, especially in older populations, than has systolic, diastolic, or mean arterial pressure.
A meta-analysis in 2000 showed that a 10 mmHg increase in pulse pressure was associated with a 20% increased risk of cardiovascular mortality, and a 13% increase in risk for all coronary end points. The study authors also noted that, while risks of cardiovascular end points do increase with higher systolic pressures, at any given systolic blood pressure the risk of major cardiovascular end points increases, rather than decreases, with lower diastolic levels. This suggests that interventions that lower diastolic pressure without also lowering systolic pressure (and thus lowering pulse pressure) could actually be counterproductive. Increased pulse pressure is also a risk factor for the development of atrial fibrillation.
Effects of medications on pulse pressure
A 2001 randomized, placebo-controlled trial of 1,292 male veterans, compared the effects of hydrochlorothiazide (a thiazide diuretic), atenolol (a beta-blocker), captopril (an ACE inhibitor), clonidine (a central α2-agonist), diltiazem (a calcium channel blocker), and prazosin (an α1-blocker) on pulse pressure and found that, after one year of treatment, hydrochlorothiazide was the most effective at lowering pulse pressure, with an average decrease of 8.6 mm Hg. Captopril and atenolol were equal as least effective, with an average decrease of 4.1 mm Hg. Clonidine (decrease of 6.3 mm Hg), diltiazem (decrease of 5.5 mm Hg), and prazosin (decrease of 5.0 mm Hg) were intermediate.
Pulse pressure and sepsis
Diastolic blood pressure falls during the early stages of sepsis, causing a widening of pulse pressure. If sepsis becomes severe and hemodynamic compromise advances, the systolic pressure also decreases, causing a narrowing of pulse pressure. A pulse pressure of over 70 mmHg in patients with sepsis is correlated with an increased chance of survival. A widened pulse pressure is also correlated with an increased chance that someone with sepsis will benefit from and respond to IV fluids.
See also
Mean arterial pressure
Cold pressor test
Hypertension
Prehypertension
Antihypertensive
Patent ductus arteriosus
References
Medical signs
Cardiovascular physiology