The electrical impedance of blood is used in biomedical applications such as impedance cardiography for monitoring blood flow. Impedance cardiography assumes a constant value for the conductivity of blood. However, this assumption has been shown to be invalid for the case of flowing blood since the conductivity is affected by flow induced changes in the orientation of red blood cells. A number of previous studies have modeled the conductivity of blood in constant flow. This study investigates the conductivity changes due to pulsatile flow as experienced during the cardiac cycle. This is achieved through the development of a theoretical model of the conductivity of pulsatile blood flowing through rigid tubes. Conductivity waveforms of pulsatile blood were generated by incorporating realistic physiological flow and cell orientation dynamics into previously reported steady flow conductivity models. Results show that conductivity correlates with the spatial average blood velocity and that features of the velocity waveform are reproduced in the conductivity signal. Conductivity was also shown to be dependent on the shape of the velocity profile. The modeled conductivity change is comparable with previously published experimental results for pulsatile blood flow, supporting the reliability of the model.

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Lymphedema is an accumulation of lymph fluid in the limb resulting from an insufficiency of the lymphatic system. It is commonly associated with surgical or radiotherapy treatment for breast cancer. As with many progressively debilitating disorders, the effectiveness of treatment is significantly improved by earlier intervention. Multiple frequency bioelectrical impedance analysis (MFBIA) previously was shown to provide accurate relative measures of lymphedema in the upper limb in patients after treatment for breast cancer. This presentation reports progress to date on a three‐year prospective study to evaluate the efficacy of MFBIA to predict the early onset of lymphedema in breast cancer patients following treatment. Bioelectrical impedance measurements of each upper limb were recorded in a group of healthy control subjects (n= 50) to determine the ratio of extracellular limb‐fluid volumes. From this population, the expected normal range of asymmetry (99.7% confidence) between the limbs was determined. Patients undergoing surgery to treat breast cancer were recruited into the study, and MFBIA measurements were recorded presurgery, at one month and three months after surgery, and then at two‐month intervals for up to 24 months postsurgery. When patients had an MFBIA measure outside the 99.7% range of the control group, they were referred to their physician for clinical assessment. Results to date: Over 100 patients were recruited into the study over the past two years; at present, 19 have developed lymphedema and, of these, 12 are receiving treatment. In each of these 19 cases, MFBIA predicted the onset of the condition up to four months before it could be clinically diagnosed. The false‐negative rate currently is zero. The study will continue to monitor patients over the remaining year to accurately ascertain estimates of specificity and sensitivity of the procedure.

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