Trial of validation of two devices for self-measurement of blood pressure according to the European Society of Hypertension International Protocol: the Citizen CH-432B and the Citizen CH-656C.

Objective: Two devices for self-measurement of blood pressure, one at the upper arm (Citizen CH-432B) and one at the wrist (Citizen CH-656C), were evaluated according to the International Protocol of the European Society of Hypertension.

Design: The International Protocol is divided into two phases: the first phase is performed on 15 selected participants with five participants in three different blood pressure ranges. If the devices passed this phase, 18 additional participants selected on the basis of the same criteria as in phase 1 were included.

Methods: Two skilled observers performed the following blood pressure measurements: five measurements were performed with the mercury standard alternating with four measurements with each of the test devices per participant. The first measurement result from each device instrument was not included in the analysis. The difference between the blood pressure value given by the devices and that obtained by the two observers (mean of the two observers) was calculated for each pair of measurements and classified into three categories (within 5, 10 and 15 mmHg). The results were compared to the pass criteria established by the European Society of Hypertension. Afterwards the number of measurement differences falling within 5 mmHg was determined for every person. At least 22 of the 33 participants should have two of their three comparisons within 5 mmHg and there should be a maximum of three participants without a measurement difference within the 5 mmHg range.

Results: Both tested devices passed the first phase of the validation process by exceeding the required number of comparisons falling within the 5, 10 and 15 mmHg error zones. Even the second phase confirmed the validation criteria with average differences between the device and the mercury sphygmomanometer of 0.7+/-4.4 and -3.6+/-4.0 mmHg for systolic blood pressure and diastolic blood pressure, respectively, for the Citizen CH-432B device and -0.7+/-6.0 and -1.2+/-4.5 mmHg for the Citizen CH-656C device. Phase 2 contains furthermore an individual analysis of the 33 participants, the requirements of which were also fulfilled by both devices.

Conclusion: The Citizen CH-432B and the Citizen CH-656C devices pass the validation recommendations of the International Protocol. They can be recommended for clinical use.