| Q: |
What is the difference between bioreactance and bioimpedance? |
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| A: |
Bioreactance and bioimpedance are non-invasive technologies which measure cardiac output, and other hemodynamic variables such as stroke volume, cardiac index, left ventricular ejection time and thoracic fluid content (TFC). Bioimpedance measurements detect electrical changes occurring with altering fluid levels in the thorax. Levels change as the left ventricular contracts and blood flows into the thoracic aorta. This causes a corresponding change in resistance within the thorax because the fluid level in the aorta increases. This change in impedance can be measured as a change in voltage passing between electrodes placed on a patient’s chest. Bioimpedance measures the amplitude of the voltage change across the thorax. |
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Bioreactance, by contrast, measures the phase or frequency shifts between an applied signal and the received signal across the thoracic wall. This differentiation is significant, and is the method by which bioreactance takes bioimpedance a step forward. The technological advancement is similar in concept to that of an AM vs. FM radio. Because FM radio detects radio signals based on frequency rather than amplitude difference in the wave form, greater fidelity is achieved. With bioreactance, phase shifts, not amplitude differences are measured also allowing for greater fidelity, leading to greater accuracy. Unlike bioimpedance, bioreactance technology—measuring phase shifts—enables usage in high ambient noise situations and during patient activity. |
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| Q: |
How does the device determine CO? |
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| A: |
It measures a frequency shift of a signal that is passed through the body. This frequency shift is correlated to the CO of the patient. |
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| Q: |
Why is CO an important parameter to monitor? |
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| A: |
It is a leading indicator of the health of the heart. |
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| Q: |
What does TFC means? How is it measured? |
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| A: |
Thoracic fluid content (TFC) refers to the fluid level within the entire thoracic cavity. TFC can be measured by reading the resistance to electrical conductivity through the chest wall. It is calculated as the inverse of the resistance or impedance (1/R) across the thorax. This qualitative measure may be used as a relative indicator of total thoracic fluid volume. Thoracic fluid volume is one tool by which doctors assess treatment options in hemodialysis where estimation of fluid balances are critical (Wynne et al, 2006). |
