Pulse Pressure Calculator (PP = SBP − DBP)
Pulse pressure (PP) is simply systolic minus diastolic — a deceptively simple but powerful cardiovascular signal. The tool also returns the mean arterial pressure (MAP) and classifies the result as low / normal / elevated using the < 40, 40–60 and > 60 mmHg bands, the textbook reading of a routine BP report.
Enter valid systolic (SBP) and diastolic (DBP) blood pressure values within physiological range.
Pulse pressure (PP)
40 mmHg
Normal
Classification (resting adult)
< 40 Normal
40–60 Elevated
> 60
Mean arterial pressure (MAP)
93 mmHg
MAP = DBP + PP/3 (Wezler formula) — the pressure that actually perfuses end organs.
Blood pressure
120 / 80 mmHg
Systolic / diastolic, measured seated and at rest.
For reference only. A formal diagnosis requires repeated measurements interpreted by a clinician.
Formula
PP = SBP − DBP MAP ≈ DBP + (SBP − DBP) / 3 (Wezler formula — the standard clinical approximation at resting heart rates)
- · Normal range: 40–60 mmHg in resting adults. PP is narrower in neonates and small children (commonly < 30 mmHg).
- · PP > 60 mmHg typically reflects loss of large-artery elasticity and is the hallmark of isolated systolic hypertension; the Framingham Heart Study showed that, after age 50, PP independently predicts coronary heart-disease risk.
- · PP < 40 mmHg (narrow PP) may indicate low stroke volume, shock, heart failure, cardiac tamponade or aortic stenosis — clinically read together with weak pulse and low SBP.
- · MAP uses the Wezler formula MAP = DBP + (SBP − DBP)/3, the best approximation at resting heart rates (60–80 bpm); for exercise or tachycardia use the Moran correction or invasive measurement instead. The Surviving Sepsis Campaign (2021) treats MAP ≥ 65 mmHg as the minimum target for adequate organ perfusion.
- · References: Franklin et al., Circulation 100, 1999; Whelton et al., 2017 ACC/AHA Hypertension Guideline; DeMers & Wachs, "Physiology, Mean Arterial Pressure", StatPearls, NCBI Bookshelf, 2023.
Frequently asked
Why is pulse pressure a stronger CV-risk predictor than systolic alone?
Because SBP and DBP reflect different haemodynamic mechanisms — SBP depends on cardiac output and peripheral resistance, while DBP is driven mainly by peripheral resistance and heart rate. PP (= SBP − DBP) captures the elastic-buffering capacity of the large arteries: in young, healthy aortas the vessel expands in systole and recoils in diastole, smoothing pulsatile flow and keeping PP narrow. With age, increased collagen and reduced elastin stiffen the aorta, the buffering shrinks and PP widens. The Framingham study showed that, after age 60, every 10 mmHg of PP raises coronary-heart-disease risk by roughly 20 %, independent of SBP and DBP. So two patients both at SBP 150 are not equal — one at 80/150 (PP 70) carries higher risk than one at 100/150 (PP 50).
At what point is a narrow pulse pressure clinically dangerous?
A widely used clinical alarm is PP < 25 % of SBP (i.e. PP/SBP < 0.25). For example, 100/80 gives PP 20 and ratio 0.20 — already in the "narrow PP" zone. The three classic causes are: (1) cardiogenic shock — PP collapses when cardiac output drops below ~4 L/min; (2) cardiac tamponade — narrow PP is part of Beck's triad; (3) severe aortic stenosis — PP typically falls below 30 mmHg. A PP under 25 mmHg combined with a thready pulse, low SBP and cold, clammy skin is a pre-shock warning and warrants urgent assessment of stroke volume and cardiac output. Caveat: athletes and highly conditioned individuals have lower resting PP (30–35) with a normal PP-to-SBP ratio — that is physiological, not pathological.
Why is MAP = DBP + PP/3 rather than just the (SBP + DBP) / 2 average?
Because the cardiac cycle is not symmetric — at resting heart rates the diastolic phase (where pressure is near DBP) takes roughly two-thirds of the cycle and the systolic phase only one-third. A simple (SBP+DBP)/2 average would therefore overstate the true time-weighted mean. The Wezler formula MAP = DBP + PP/3 = DBP + (SBP − DBP)/3 implicitly weights SBP at 1/3 of the cycle and DBP at 2/3, and agrees with invasive arterial measurements to within ~5 mmHg at heart rates of 60–80 bpm. As heart rate rises (exercise or tachycardia) the systolic share grows and Wezler under-estimates MAP; the Moran correction MAP = DBP + PP × (0.33 + HR × 0.0012) is then preferred, or an arterial line for real-time integration. In ICU practice an invasive line samples the entire waveform and time-integrates it for the most accurate MAP.
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