Lillian Chan’s research while affiliated with University of Alberta and other places

Objective Understanding of how oscillometric waveforms (OMW) vary between pregnant and nonpregnant individuals remains low. An exploratory analysis was completed to assess for quantitative and qualitative changes in OMW and oscillometric envelope features in pregnancy. Design and methods Eighteen pregnant individuals (over 20 weeks gestational age) and healthy, nonpregnant (HNP) women were recruited. Six HNP were matched to six healthy pregnant (HP) women, and six pregnant women with a hypertensive disorder of pregnancy (HDP) by age, arm circumference, and cuff size. Blood pressure measurements were completed per the International Organization for Standardization (ISO) protocol using a custom-built oscillometric device as the test device and two-observer mercury auscultation as the reference measurement. Auscultatory blood pressure and blood pressure derived from slope-based and fixed ratio algorithms were determined. OMW and envelope features were compared among groups. Results In HNP, HP, and HDP groups respectively: mean auscultatory blood pressure (systolic mean ± SD/diastolic mean ± SD) was 103.4 ± 12.2/67.1 ± 7.9; 109.5 ± 3.1/58.1 ± 6.4; 135.6 ± 18.9/85.1 ± 14.2 mmHg. HDP had significantly higher auscultatory systolic and diastolic blood pressure than the HP group ( P = 0.001). The pregnant groups had a lower average pulse width (mean ± SD: HNP = 0.8 ± 0 s, HP = 0.6 ± 0.1 s, HDP = 0.6 ± 0.1 s; HP vs. HNP mean difference [adjusted P value]: 0.2 [ P = 0.004], HDP vs. HNP 0.1 [ P = 0.018]) compared with the HNP group. The HDP group had a larger area under the OMW envelope than the HNP group (mean ± SD: HNP = 22.6 ± 3.4; HDP = 28.5 ± 4.2; HDP vs. HNP mean difference [adjusted P value]: 5.9 P = 0.05). Conclusion In this exploratory work, differences in the OMW morphology and parameters were found in pregnancy and in hypertensive disorders of pregnancy compared with healthy controls. Even small differences may have important implications in algorithm development; further work comparing OMW envelopes in pregnancy is needed to optimize the algorithms used to determine blood pressure in pregnancy.

Hypertensive disorders of pregnancy are leading causes of maternal and perinatal morbidity and mortality. Automated blood pressure (BP) measurements are being used in clinical practice; however, understanding of how oscillometric waveform vary between pregnant and non-pregnant individuals remains low. Pregnant individuals over 20 weeks gestational age and healthy, non-pregnant women were recruited. Healthy, non-pregnant women (HNP) were matched to healthy pregnant women (HP), and pregnant women with a hypertensive disorder of pregnancy (HDP) by age (± 10 years), arm circumference (± 6 cm), and BMI at the time of BP measurement (± 13 kg/m2). There were seven individuals in each group for a total of 21 participants. BP measurements were done per the International Organization for Standardization (ISO) protocol using a custom-built oscillometric device as the test device and 2-observer mercury auscultation as the reference measurement. Four pairs of auscultatory measurements and four oscillometric measurements were obtained for each participant. Baseline demographics, auscultatory BP and BP derived from slope-based and fixed ratio algorithms were determined. Oscillometric waveform and envelope features were compared among groups. In HNP, HP, and HDP groups respectively: mean age was 31.3 ± 4.8; 32.1 ± 3.6; 32.0 ± 4.4 years; arm circumference 31.9 ± 3.3; 32.3 ± 4.9; 34.0 ± 3.3 cm; BMI 26.8 ± 3.8; 32.0 ± 7.2; 32.4 ± 3.7 kg/m2; mean auscultatory BP (systolic/diastolic) 103.3 ± 11.1/66.5 ± 7.4; 110.6 ± 4.0/56.9 ± 6.5; 132.6 ± 19.0/83.9 ± 13.3 mmHg. HDP had significantly higher auscultatory systolic (P < 0.05) and diastolic (p < 0.01) BP than the other groups. The pregnant groups (HP, HDP) had significantly higher heart rate (p < 0.01); higher pulses (p < 0.05) in the oscillometric waveform (OMV); lower average width in the pulses (p < 0.01); higher pressure amplitude at which the OMW peaks (p < 0.05) with longer time to reach this maximum pressure amplitude (p < 0.05); greater area under the curve (p < 0.01). Compared to HNP, the HDP showed significantly skewed OMW to the right (p < 0.01); greater spread in the OMW envelope (p < 0.05) and lesser random variation in the OMW envelope (p < 0.01). A typical OMV with the 3 groups superimposed is demonstrated in Figure 1. Significant differences in the oscillometric waveform morphology and parameters were found in pregnancy and in hypertensive disorders of pregnancy compared to healthy controls. These results suggest that pregnancy-specific algorithms may be required to optimize accuracy for oscillometric BP measurement. Healthy non-pregnant, healthy pregnant, and pregnant with a hypertensive disorder of pregnancy oscillometric waveforms superimposed.