Electrical Impedance Of Blood Research Articles

Microfluidic device and system for point-of-care blood coagulation measurement based on electrical impedance sensing

Blood coagulation tests are an integral part of diagnosis and treatment of patients with cardiac disorders. The activated partial thromboplastin time test (aPTT or APTT) is performed on a large scale, in laboratories, to monitor the functioning of the intrinsic and common pathways of the blood coagulation cascade and the concentration of anticoagulants such as heparin among patients. A polydimethylsiloxane (PDMS) based microfluidic device has been fabricated and tested to perform APTT as a point-of-care device using whole blood samples by detecting the change in electrical impedance of blood during coagulation. A portable setup consisting of the device and a lock-in amplifier circuit was built and tested for repeatability and stand alone usage. A frequency sweep test was performed on the device and the optimal frequency of operation for maximum output sensitivity was determined. The devices were also tested for their sensitivity to different concentrations of heparin and found to exhibit an expected increase in coagulation time for increasing heparin concentration.

The Electrical Impedance of Pulsatile Blood Flowing Through Rigid Tubes: A Theoretical Investigation

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.

Quantitative correlations among fibrinogen concentration, sedimentation rate and electrical impedance of blood.

Blood cells from 8 normal subjects, anticoagulated with EDTA, were washed twice with saline solution (100 mmol/l) and resuspended into saline solutions of different concentrations of human plasma fibrinogen. The erythrocyte sedimentation rates (ESRs) of these suspensions were determined by the Westergren method, and their resistance Rp and capacitance Cm were determined by measuring the impedances at three frequencies 100 kHz, 800 kHz and 1.2 MHz. The results showed that the logarithm of the ESR was proportional to the concentration of fibrinogen, Fb (g/l), expressed as: ln(ESR) = 0.468Fb - 0.10, (r = 0.96); and the haematocrit-normalised resistance R'p and capacitance C'm were both directly proportional to the concentration of fibrinogen, R'p = 3.99Fb + 465.0, (r = 0.87), and C'm = 49.7Fb + 628.2, (r = 0.96). The influence of fibrinogen on the impedance might partly be the result of interfacial polarisation and/or of red cell rouleaux formation. The results are useful for understanding the mechanism of the association between the impedance and the ESR of blood, and for finding means of improving the accuracy when estimating the ESR by the electrical impedance method.

New applications of electrical impedance of human blood.

The electrical impedance parameters of human blood, that is, plasma resistance Rp, cell interior resistance Ri and cell membrane capacitance Cm, were determined by measuring impedance amplitudes at three different frequencies, 0.1, 0.8 and 1.2 MHz. Several new findings have been obtained. The fibrinogen in normal blood raised Rp and Cm by about 4% and 20%, respectively, and serum proteins contributed to the capacitance by about 14%. The results imply that the electrical impedance of blood may reflect certain diseases that involve abnormal compositions of certain plasma proteins. Measurement on 62 samples with various erythrocyte sedimentation rates (ESR) demonstrated that both Rp and Cm were proportional to ESR, implying that the impedance measurement might be an alternative method for quick estimation of ESR. During in vitro storage of blood at 4 degrees C, both Rp and Cm decreased with time, about -20% for Cm after four weeks of storage. The results imply that the impedance change might be a useful index for evaluating the quality of stored blood.

Electrical impedance alterations of red blood cells during storage.

The electrical impedance of blood is determined mainly by the resistance of the plasma (Rp), resistance of the red cell interior fluid (Ri), and capacitance of the cell membranes (Cm). These parameters were measured on 10 stored blood samples consecutively during 4 or 5 weeks of storage at 4 degrees C, once every week. Compared to the values of fresh samples, a statistically significant decrease in Rp was found mainly during the first week of storage, Ri did not decrease significantly until after 3 weeks, whereas Cm decreased progressively with time. These alterations can be explained by known red cell lesions during storage. The results indicate that electrical impedance measurements might be useful for monitoring red cell ageing and assessing the quality of stored red blood cells.

Electrical impedance and erythrocyte sedimentation rate (ESR) of blood

The electrical impedance of blood is primarily determined by plasma resistance R p, cell interior resistance R i, and cell membrane capacitance C m. These impedance parameters were measured for 62 samples with various erythrocytes sedimentation rates ( ESR = 1−150 mm/h). A formula for estimating ESR by R p and C m was obtained by linear regression as: ln (ESR) = 10.16 −0.016 · ƒ 0, (r = 0.974, P < 0.001) , where ƒ 0 = 10 9/(2π · R p100 · C m100 ) , defined as the effective characteristic frequency in kHz, R p100 = R p/ h in Ωcm, C m100 = C m/ h in pF/cm, h is the haematocrit in decimal. The 95% confidence intervals for the coefficients in the above equation were 9.73 to 10.59 and −0.017 to −0.015. The origin of the association was found reasonable since factors increasing the ESR, i.e., the concentration of some plasma proteins and the size of the blood cells, also elevate the capacitance. The results imply that the impedance measurement might be an alternative method for fast determination of the ESR.

Study of the electrical impedance of blood from house painters

Using a four-electrode technique the electrical impedance was measured at 150 kHz (100 microA) on whole blood samples from 13 male house painters (age 19-49 years; median 35 years) exposed occupationally to vapors from alkyd paints containing organic solvents and from a control group of 7 healthy unexposed men (age 27-53 years; median 37 years). The blood impedance of the two groups was monitored prior to and 9 days after an initial administration of acetylsalicylic (600 mg). The resistivity calculated from the impedance of whole blood from the painters remained significantly higher than the corresponding values for the controls. The hematological values for the two groups were within normal ranges, although the painters had significantly higher platelet counts than the controls. Effects of long-term exposure of the painters to volatile solvents are discussed.

The electrical impedance of plasma: A laboratory simulation of the effect of changes in chemistry

To evaluate the role of plasma chemistry in the genesis of electrical impedance of blood, a laboratory simulation was performed using solutions prepared so as to mimic plasma chemistry abnormalities that are seen in the critically ill. There was a 15% increase of impedance due to decrease in sodium chloride concentration from 140 mmol/L to 120 mmol/L, and a 12% decrease of impedance due to increase in sodium chloride to 160 mmol/L. Impedance changes secondary to other chemistry abnormalities were small and probably not significant, with the exception of a change of albumin concentration from 80 gm/L to 50 gm/L, which induced a 6% increase in impedance. Using this data, a model was constructed to predict changes in whole blood resistivity, and this was extrapolated in two simulations of plasma chemistry abnormalities to predict alterations of calculated impedance stroke volume in excess of 5%.

Changes in the Electrical Impedance of Blood during Coagulation

REPORTS on the impedance changes of blood during coagulation have been conflicting, and many have concluded that there is no significant impedance change which could be related to the coagulation process1–5. In 1948, however, Rosenthal and Tobias6, using improved techniques, demonstrated a significant increase in impedance following coagulation, but the technique never came into practical use. Moreover, though some workers confirmed the observations7, others claimed to obtain conficting results8.