Graduation Year


Document Type




Degree Granting Department

Electrical Engineering

Major Professor

Wilfrido Moreno, Ph.D.

Co-Major Professor

Jeffrey Harrow, Ph.D.

Committee Member

James T. Leffew, Ph.D.

Committee Member

Paris Wiley, Ph.D.

Committee Member

Horace Gordon, M.S.E.E.


Impedance plethysmography, Perfusion skin monitoring, Tissue impedance, Matlab, LabView


The pressure ulcer is a well-known clinical problem that has plagued many patients in acute-care hospitals and chronic-care facilities. The pressure ulcer has the potential to diminish the quality of a patient's life by hindering the person's physical and emotional well-being. In addition, pressure ulcers are a high-cost problem. Past studies have shown that costs related to the treatment of pressure ulcers have reached 1.335 billion dollars a year in the United States alone.

A pressure ulcer is defined as a lesion created by unrelieved pressure, which causes tissue ischemia and subsequently damages the underlying tissue. This sequence of events is mainly centered on ischemia. Ischemia is a condition created by an insufficient flow of blood to an organ or part of an organ such as the skin. The outcome of ischemia is cell death at the tissue level, which is commonly termed necrosis.

In the past, researchers employed several different non-invasive techniques in order to detect changes in the condition of human skin when blood flow was restricted. The two most commonly used practices were Laser Doppler Velocimetry and Continuous Wave Ultrasound. Laser Doppler Velocimeter is used to measure cutaneous blood flow in a study region. The moving red blood cells in blood vessels cause a Doppler shift of incident laser light, which correlates with the velocity of blood flow. Continuous Wave Ultrasound involves an ultrasound signal, which is transmitted into the skin. The change in frequency of the reflected signal with respect to the transmitted signal provides an indication of blow flow.

The objective of this research was to examine a method for the detection of arterial blood flow, which utilized the 4-electrode sensor for the measurement of Tissue Impedance or the Bio-impedance method. The system developed, for the synchronous detection method, consisted of both analog hardware and software tools. The analog hardware utilized synchronous detection. The software monitored and performed mathematical operations on the retrieved data. The system developed during this research demonstrated the ability to measure the pulsatile impedance of the skin and present the results in a fashion useful to healthcare providers.