In one sentence
Three figures VT works out from your blood pressure, and from the age of 50 follows day by day: pulse pressure, the gap between systolic and diastolic; mean arterial pressure, the average pressure pushing blood through your arteries across a heartbeat; and fractional pulse pressure, how large each pulse is compared with that average, which over time reflects how flexible your arteries are.
Why it matters
Each heartbeat pushes a volume of blood into the aorta, and a supple aorta stretches to take it and recoils to keep blood moving between beats, so the pulse arrives at the arm smoothed; as the large arteries stiffen with age, less of each stroke is cushioned, systolic pressure rises, diastolic falls, and the gap between them widens. The Framingham Heart Study followed 6,539 adults aged 20 to 79 for 20 years and found a gradual shift in which pressure carried the information: under 50, diastolic pressure was the strongest of the three (hazard 1.34 per 10 mm Hg) and pulse pressure carried none; 50 to 59 was a transition in which all three were comparable; and from 60, pulse pressure was the strongest (hazard 1.24 per 10 mm Hg) and diastolic pressure ran the other way (Franklin 2001). An earlier Framingham analysis of 1,924 adults aged 50 to 79 found that at any systolic pressure of 120 mm Hg or more, coronary heart disease rose as diastolic pressure fell, and that neither systolic nor diastolic pressure outperformed the pulse pressure (Franklin 1999). The counterweight belongs beside it: across all ages 40 to 89 in the one-million-adult meta-analysis, pulse pressure was much less informative about vascular mortality than the level of pressure itself (Lewington 2002). Read together, the three papers say what VT does: pulse pressure is a weak number on its own and below 50, and a useful one as your own trend from 50.
What moves it
Everything that moves blood pressure, and three things of its own. Heart rate: a slower heart fills more between beats, so each stroke is larger and the pulse pressure wider, which is why a reading after a hard session or a short night is not comparable with a rested one. Hydration and posture, which change the stroke volume. And the stiffness of the large arteries, which changes over months with age, weight, blood pressure itself, smoking, and aerobic exercise. In younger people the pressure wave is amplified between the heart and the arm, so the arm's pulse pressure overstates the central one; this is the reason the indices start at 50.
How to measure it well
Exactly as blood pressure: the same cuff, arm, posture and routine, because a ratio of two readings inherits the noise of both. One value a day, from the day's average, is the least that makes the figures stable; a morning reading alone is better than a mixed bag.
How Vitality Tracker uses it
VT shows all three beside your readings at any age. From 50, with your date of birth in your profile, it also follows the fractional pulse pressure and the mean arterial pressure day by day, from your very first reading. Each day's figures are compared with the average of your previous seven readings, and a change of less than 2 percent counts as stable; the direction comes with a plain reading, for example "improved arterial buffering" when the fractional pulse pressure has fallen against them. The indices are shown on the arteries panel beside the pressure itself and the vascular age; they do not enter the Vitality Score, where the pressure and the vascular age already stand for the arteries. In the engine the fractional pulse pressure is called the pulsatile stress ratio.
How far to trust the number
Calculated, from a measured input. Pulse pressure and mean arterial pressure are exact arithmetic on the day's average; the mean arterial pressure formula is an approximation that assumes a resting heart rate, and at high rates the true mean sits nearer the midpoint. The fractional pulse pressure is a ratio of two noisy numbers, so a single day's value moves by several percent on measurement noise alone, which is why the comparison is with a week, not a day, and why 2 percent is called stable. The figure describes the pressure at the arm, not at the heart, and in the first years after 50 the two are still not the same.
Sources
- Franklin SS, et al. Does the relation of blood pressure to coronary heart disease risk change with aging? The Framingham Heart Study. Circulation 2001;103:1245–9. doi:10.1161/01.cir.103.9.1245
- Franklin SS, et al. Is pulse pressure useful in predicting risk for coronary heart disease? The Framingham Heart Study. Circulation 1999;100:354–60. doi:10.1161/01.cir.100.4.354
- Lewington S, et al. Lancet 2002;360:1903–13. doi:10.1016/S0140-6736(02)11911-811911-8>)
- Vitality Tracker, How it works (the blood-pressure measures); the engine catalogue of 15 October 2026 (the PPf and MAP engine).