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’.