How this instrument works
Pressure half-time is the time it takes the pressure gradient across the mitral valve, measured by continuous-wave Doppler, to fall to half its peak value early in diastole. A wide-open valve lets that pressure equalize almost instantly; a narrowed one holds the gradient up longer because blood keeps struggling through a small opening. Liv Hatle and colleagues in Oslo noticed in the late 1970s that this decay slows down in a remarkably predictable way as the valve narrows, and fit a simple constant, 220, that converts the half-time directly into a valve area in square centimetres: divide 220 by the half-time in milliseconds.
The appeal is speed and simplicity. This site's other valve-area instrument, the Gorlin equation, needs cardiac output, a flow period, heart rate, and a mean pressure gradient — a small panel of catheterization or echo measurements combined through two steps of arithmetic. Pressure half-time needs exactly one number, read straight off a Doppler trace, because the physics of how fast a pressure difference dissipates across a fixed orifice already encodes the orifice's size. Hatle, Angelsen and Tromsdal published the relationship in 1979, and it became one of the most widely used bedside measurements in echocardiography specifically because it asks so little of the person taking it.
The shortcut has real limits. It assumes the left atrium and left ventricle behave like two chambers connected only by the mitral valve, so conditions that add or remove volume from that closed system throw the timing off. Significant aortic regurgitation raises left ventricular diastolic pressure independently and shortens the apparent half-time, making a valve look tighter than it is. Right after balloon mitral valvuloplasty, chamber compliance is still settling and the relationship has not been shown to hold reliably for a period afterward. Outside those settings, in ordinary mitral stenosis, it tracks catheter-measured area closely enough that it largely replaced more elaborate calculations at the bedside.
- Enter Pressure half-time in milliseconds — the time from peak early-diastolic gradient to half that value, read off a continuous-wave Doppler trace across the mitral valve.
- Read Mitral valve area in square centimetres — the instrument divides the constant 220 by the half-time you entered; no other inputs are needed.
Worked example — 150 ms pressure half-time
A Doppler trace shows the mitral gradient falling to half its peak value in 150 ms. Divide the constant: 220 ÷ 150 = 1.47 cm² — a valve area in the moderate mitral stenosis range, obstructed enough to matter but well short of severe.
Two comparisons show how sensitive the ratio is to timing. A half-time of exactly 220 ms gives exactly 1.0 cm² — the constant itself is calibrated so 220 ms lines up with a 1.0 cm² valve, a useful anchor point to remember. Drop the half-time to 100 ms, meaning the pressure equalizes twice as fast, and the area comes out to 2.2 cm², outside the stenotic range entirely — a fast half-time means a wide-open valve.
Questions
Why does a longer half-time mean a smaller valve area?
Because the constant sits in the numerator. A long half-time means the pressure gradient across the valve is slow to equalize, which happens when the opening is small enough to keep restricting flow well into diastole. Divide 220 by a large number and the quotient — the calculated area — comes out small; the mathematics simply mirrors the physiology, where a stiffer bottleneck holds pressure up longer.
Where does the constant 220 come from?
Hatle, Angelsen and Tromsdal derived it in 1979 by comparing Doppler-measured half-times against catheter-measured mitral valve areas and fitting the ratio between them. It is an empirical calibration specific to the mitral valve's geometry and the hemodynamics of left atrial emptying, not a general physical constant — which is why this shortcut, unlike the Gorlin equation, is not used for other valves.
How does this compare to the Gorlin equation on this site?
The Gorlin equation needs cardiac output, a flow period, heart rate, and a mean gradient — a fuller hemodynamic picture, useful for any of the four heart valves. Pressure half-time needs one Doppler timing measurement and works only for the mitral valve, trading versatility for speed. In routine mitral stenosis without complicating lesions, the two methods generally agree well enough that half-time is the one used day to day.
When does pressure half-time give a misleading answer?
Two situations are well documented. Significant aortic regurgitation raises left ventricular pressure independently of the mitral valve and shortens the apparent half-time, understating how tight the valve actually is. Soon after balloon valvuloplasty, the left atrium and ventricle are still equilibrating to the newly opened valve, and the timing relationship has not settled into the pattern it was calibrated on — repeat measurements after some stabilization are more trustworthy than one taken immediately post-procedure.
Does this replace a full echocardiogram?
No — it is one number extracted from one part of the study. A complete echocardiographic assessment of mitral stenosis also looks at valve shape, planimetered area, left atrial size, and pulmonary pressures, because any single measurement, this one included, can be thrown off by the specific conditions described above. Pressure half-time is a fast, well-validated cross-check, not a replacement for the full picture.
References
- Hatle L, Angelsen B, Tromsdal A, 1979, Circulation — original derivation (PubMed)
- American Heart Association Journals — Circulation, full text of the 1979 paper
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.