Determination of central blood pressure by a noninvasive method (brachial blood pressure and QKD interval): a noninvasive validation

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We validated against invasive measurements a measure of central SBP based on the QKD interval. The present objective is a comparison to the SphygmoCor device.

Materials and methods:

A first cohort was used to redefine an algorithm for estimating ascending aorta SBP (cSBP) with respect to SphygmoCor. This algorithm was then tested in a second cohort under static conditions and in a third cohort during a head-up tilt to study blood pressure variations.


The first cohort (36 patients, mean age: 46 ± 20 years, SBP: 114 ± 19 mmHg) defined the estimation algorithm as cSBP = 62.687 + 1.35 × meanBP-0.207 × heart rate−0.251 × height−0.1 × QKD (mean difference with SphygmoCor = 0 ± 7 mmHg).


In the second cohort (105 patients, mean age: 51 ± 19 years, SBP: 132 ± 22 mmHg), the average difference between the two techniques was 2 ± 6 mmHg (R2 = 0.93). The dynamic cohort included 31 patients (mean age: 49 ± 23 years, SBP: 110 ± 19 mmHg) with 224 pairs of measurement. We studied the changes in central blood pressures compared with the basal state of each of the two techniques during head-up tilt. With QKD, the average cSBP was 104 ± 19 mmHg, the average variation was −13.00 mmHg ± 15 (range 7–74 mmHg). With SphygmoCor, average cSBP was 101 mmHg ± 18, the average variation was −14 mmHg ± 16 (range 2–81 mmHg). The variations in blood pressure with the two techniques were well correlated (R2 = 0.93).


cSBP estimation based on the QKD interval is comparable in precision to the SphygmoCor. Its ability to measure cSBP variations suggests that it could be employed for ambulatory measurements over 24 h.

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