UBC Theses and Dissertations
Insights into the effect of blood pressure and pregnancy on the PPG signal Ramos Macias, Barbara Monserrat
Introduction: Hypertension in pregnancy, characterized by high blood pressure, is one of the three most common causes of maternal death. Photoplethysmography (PPG) is a portable, non-invasive and low-cost technique, which might have the potential to detect hypertension in pregnancy along with measuring three vital signs: oxygen saturation, heart rate, and respiratory rate. Currently, efforts have been made to estimate blood pressure and detect hypertension with the PPG signal. Objectives: The primary objective of this study is to describe the effect of pregnancy and blood pressure on the PPG signal. Methods: We calculated the average pulse per month of gestational age from 5,072 PPG signals of normotensive women to create a visual representation of a normal pregnancy effect on the PPG morphology. We fitted a linear model using the gestational age, blood pressure, and their interaction to predict PPG features. The PPG features were extracted from 11,412 PPG signals of pregnant women. The PPG features were calculated using four algorithms developed to locate the: dicrotic notch, diastolic peak, systolic peak, start of the pulse, and second derivative waves. Results: We observed PPG morphology changes based on the gestational age in normal pregnancy. The association with blood pressure described in the literature for non-pregnant subjects of some PPG features such as heart rate can change in pregnancy based on the gestational age. The obtained results of the four algorithms are: 1) pulse location algorithm with an accuracy of 97.67% and 98.1% for the start of the pulse and systolic peak location, respectively; 2) pulse verification algorithm improved pulse location positive predictivity; 3) equal accuracy between the ʻaʼ and ʻbʼ waves and the pulses location; and 4) reliable dicrotic notch, diastolic peak and ʻeʼ location based on the comparison with a high-performance dicrotic notch algorithm and visual inspection. Conclusion: The normal cardiovascular changes seen during pregnancy consistently affect the PPG signal and can be visually represented. The gestational age has a significant effect on the PPG detection of hypertension in pregnant women.
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