Date of Award

Spring 5-2024

Author's School

McKelvey School of Engineering

Author's Department

Biomedical Engineering

Degree Name

Master of Science (MS)

Degree Type




A Thesis on the Development of a Wearable Short-Wave Infrared Photoplethysmography Device for Detection and Monitoring of Hemodilution During Postpartum Hemorrhage


Hannah Gruensfelder

Master of Science in Biomedical Engineering

Washington University in St. Louis, 2024

Professor Christine O’Brien, Chair

Postpartum hemorrhage (PPH), the leading cause of maternal death and morbidity, affects nearly 14 million people worldwide each year, disproportionally impacting racial minorities and people in low resource settings. A timely diagnosis of PPH is key in providing optimal patient care, as an estimated 90% of deaths due to PPH are preventable with early diagnosis and treatment. Early diagnosis is especially critical where there is limited access to blood transfusion and surgical care. There are few tools for diagnosing and monitoring PPH, and it is currently diagnosed by visually estimating blood loss and monitoring vital signs. In many clinical settings, visual estimations significantly underestimate blood loss and often fail to detect internally retained blood. During early hemorrhage, patients experience sudden changes in vascular equilibrium, and the body compensates to keep the heart rate and blood pressure stable despite moderate to large blood loss volumes. In young, healthy patients, such as those of child-bearing age, vital signs may only begin to fluctuate with large levels of blood loss and can therefore reliably identify only late stages of PPH, by which time surgical intervention or blood transfusions are required. In addition to detecting and diagnosing PPH early, it is also extremely important to monitor patients after beginning treatment for PPH. Current treatment options include medications, blood transfusions, and surgical interventions such as laparotomy and hysterectomy, which all can present significant risks to the patient. It is imperative that patients be closely monitored after introduction of treatment, however, patient monitoring is currently limited to in-patient hospital care using serial blood draws and vital sign monitoring devices.

One compensatory mechanism during PPH is hemodilution, in which water from the extravascular space is drawn into circulation to increase blood volume, resulting in a reduced hemoglobin concentration. If hemodilution is severe, it can compromise the patient's ability to oxygenate their tissues and cause coagulopathies, creating a medical emergency. There is an urgent need for a tool that can detect PPH early and monitor its progression, along with the introduction of treatments.

Absorption spectroscopy, already used in many optical device designs, is a promising technique for identifying the best wavelengths for noninvasive monitoring. However, absorption spectroscopy has historically covered only the visible (VIS) to near-infrared (NIR) wavelength ranges. Thus, many optical devices use VIS and NIR components, which can cause inaccurate results in people with skin darkly pigmented by melanin. Melanin strongly absorbs light at shorter wavelengths but is a weaker absorber at short-wave infrared (SWIR) wavelengths, making the SWIR a better wavelength range for illuminating skin with high melanin content. However, because little is known about how biological tissue absorbs in the SWIR, characterizing common biological absorbers spanning the VIS to the SWIR wavelength ranges will provide the spectra necessary to create SWIR optical devices.

Here, we describe the design and development of a prototype wearable SWIR photoplethysmography (PPG) device to detect and monitor hemodilution during and after PPH. This low-cost wearable hemodilution sensor will provide continuous monitoring for early diagnosis of PPH and will prevent dangerous blood loss. Importantly, the use of SWIR LEDs and detectors will minimize the effects of melanin absorption, minimizing the racial disparities affecting other light-based diagnostics. This device has high potential to be successfully translated as an inexpensive, fully wireless, wearable watch, finger clip, or necklace that will be accessible to patients across the world, particularly where PPH mortality is the highest.


English (en)


Christine O'Brien

Committee Members

Christine O'Brien Leonid Shmuylovich Mikhail Berezin