Procedure
Phase 1
In order to evaluate the clinical performance of the CDXP we used an adjusted version of the ESH-IP 2010 that is suitable for non-pregnant validation studies to make it clinically more applicable for use in a pregnant population. First, all measurements were conducted by the same observer, as resembles the outpatient clinical situation. Second, a total of two measurements per tested device were performed for the same reason. Third, the blood pressure ranges from the ESH-IP 2010 were lowered to the physiological blood pressure ranges during pregnancy. Fourth, we used an aneroid blood pressure device as a gold standard as a mercury blood pressure device is not allowed in our hospital.
After their regular check-up in the outpatient clinic, women were asked for participation in this study. After informed consent, women were seated in a comfortable chair in a room with a comfortable temperature, refrained from talking and moving around for a period of 10 minutes. A total of six blood pressure measurements was conducted in two rounds on each participant. Each round consisted of two measurements with the CDXP, the Omron M6 Comfort (randomization was performed to determine the consecution) and the aneroid manometer. All measurements were performed on the non-dominant arm because participants will use their dominant hand to fasten the wrist cuff at home. Maternal age, height, weight, gestational age, circumference of upper arm and wrist of the non-dominant side and the use of antihypertensive medication were documented, as well as any peculiarities (arrhythmia, error of the measuring device, poor sound quality or others).
Phase 2
In the second phase we focused on the performance of the CDXP for HBPM. Measurements were performed under three conditions: standard office measurement, office self-measurement and home self-measurement. Prior to their appointment a doctor’s assistant carried out the standard office blood pressure measurement with the Welch Allyn 5300P. After their appointment, patients were asked to conduct two office-self-measurements using the CDXP, receiving elaborate instructions. After the office self-measurement the CDXP was given home along with written instructions and women were asked to measure their blood pressure at home after ten minutes of rest at four timepoints during the day: around 8:00 am, 12:00 pm, 18:00 pm and 22:00 pm. At each timepoint of measurements patients were asked to carry out two blood pressure measurements with a one-minute interval. The following patients’ characteristics were collected: BMI before and during pregnancy, age, amenorrhea duration, parity, the diagnosis of pre-existing or gestational hypertension, upper mid arm and wrist circumference.
After the blood pressure measurements patients’ experience was evaluated by questionnaire, containing fifteen questions (Table 3). Ten questions, regarded the user’s experience, were based on the system usability scaled (SUS)23. Five other general questions were included as well. All questions were scored using the five-point Likert-scale, ranging from ‘strongly disagree’ to ‘strongly agree’.