A comparison among oscillometric waveforms in healthy nonpregnant women, pregnancy and hypertensive disorders of pregnancy.

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.