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Impedance cardiography (ICG) which is also known as electrical impedance plethysmography (EIP) is a technique that incorporates the use of feelers in hemorheology to sense the blood properties that stream in an individual’s thorax. Leondes  describes the ICG technique to involve the placement of four dual disposable sensors on the neck and chest areas to transmit and detect any changes that might exist in the thorax. These changes and transmissions are usually in the form of electrical transmission and changes or impedance transmissions and changes.
According to Feldman , changes are then used to measure and calculate the hemodynamic parameters that will be used by physicians and clinicians in patient assessment, diagnosis and treatment decisions. The thorax in ICG is viewed as a cylindric volume conductor that undergoes alternating currents that are applied across the thorax. The changes that occur as a result of using ICG to measure hemodynamic parameters relate the changes to the thorax to dynamic events such as blood flow, stroke volume, blood pressure and ventilation.
ICG is used in various contexts one of which is in evaluating the exercise response of patients that have a left ventricular dysfunction as described by Hetherington et al . Another application for impedance cardiography is in predicting the mortality rates of emergency patients that have severe sepsis and septic shock as described by Napoli et al  in their study. It is also used in monitoring hemodynamic changes during laparoscopy procedures in children as explained by Kardos et al  and it is also used in the studying of patients that have suffered cardiac or heart failure as described by Hubbard et al  and in the study of postural stress. The use of impedance cardiography has grown into a tool that can be used in the assessment of stroke volumes to exercise. The continuous development of electrical impedance cardiography has made the method to be suitable in routine exercise testing.
The use of impedance cardiography in measuring standard clinical exercises is beneficial to fields of medicine such as cardiology and pulmonary medicine. The evaluation of hemodynamic responses in heart failure has proven to be a useful tool in clinical management activities as explained by Sodolski and Kutarski . Hemodynamic assessments reduce the maximal exercise capacities of patients that suffer from the chronic obstructive pulmonary disease (COPD) where these assessments are preferred to pulmonary function tests because pulmonary tests provide a poor prediction of oxygen consumption during peak exercise. The direct assessment of cardiac functions in patients that suffer from COPD provides clinicians or physicians with valuable information that can be used to evaluate patients and develop appropriate diagnosis and treatment decisions .
The use of electrical impedance cardiography has been identified as a suitable alternative to pulmonary testing as the method can be able to incorporate hemodynamic measurements during the standard testing exercise. A study conducted by Bogaard et al  of 22 male patients that suffered from COPD showed that a difference existed between patients and controls when it came to hemodynamic responses to exercise. The study showed that an increase in the stroke volume of the COPD patients during exercise was greatly diminished as hemodynamic assessments were performed. The study also showed that during peak exercise, there were no differences in the stroke volume as a result of a decrease at the end of the exercise.
The stroke volumes only increased during the initial stages of the exercise which was attributed to an increase in the end-systolic volumes which are also known as ESV. According to the study, stroke volumes and end-systolic volumes experienced changes that were caused by muscle masses, changing blood volumes, the heart size and the neuroendocrine functions of the individual. The results of the study showed that aberrant hemodynamic performances were able to be assessed through the use of an electrical impedance cardiograph. These aberrant responses were related to the severity of the chronic obstructive pulmonary disease in the patients which limited the exercise performance of severe airflow obstruction . The above sections which have focused on the field of impedance cardiography and the assessment of hemodynamics response to exercise have formed the proposal for the thesis under study.
Purpose and Rationale
The section will involve a discussion of the purpose and rationale of bioimpedance as well as the development of a thesis which is bioimpedance cardiography and an examination of the thesis statement which is “the use of bioimpedance cardiography to measure and evaluate hemodynamic parameters during stress conditions. According to Maisel , Bioimpedance cardiography is a method that is used in evaluating the cardiac output of patients that have suffered a cardiac failure or heart strokes during exercise assessments. Bioimpedance relies on the proportional changes that take place as a result of alternating currents that exist in the thoracic cavity. The main purpose of bioimpedance cardiography according to Rosenberg and Yancy  is to determine the stroke volumes, fluid content in the thorax and cardiac outputs.
Bioimpedance cardiography involves the use of impedance cardiography to monitor and detect changes in the thoracic cavity in response to an applied current to the neck and chest. This method is used to detect stroke volumes in heart failure patients and it is also useful in calculating and measuring the cardiac output of the patient’s heart rate. Bioimpedance cardiography have evolved over the recent years to reflect changes and innovations in computing power. Albert  argues that the use of these units in preclinical trials which have involved the experimentation of dogs and pigs under anesthesia have shown that a good correlation exists when other techniques and approaches are used in measuring cardiac outputs.
Methodology of Bioimpedance Cardiography
The methodology of bioimpedance cardiography has been used in the measurement of hemodynamic parameters. A study conducted by Santoro et al  on 52 uraemic patients that were undergoing a hemodialysis session involved the use of bioimpedance cardiography to record the beat-to-beat changes that took place within the hemodynamic parameters that included stroke volumes, cardiac outputs, heart rates, blood pressures and arterial pressure. The equipment that was used during the hemodialysis session included a personal computer, a pressure recorder and an electrical bioimpedance cardiography monitor. The results of the study showed that 46 of the 52 patients experienced dialysis-induced hypotension during the hemodialysis session.
Their arterial and blood pressures reduced considerably during acute hypotension episodes but they experienced an increase in cardiac outputs. Their heart rates and stroke volumes did however not experience any significant changes during the hemodialysis session . The results of the study showed that bioimpedance cardiography can be used to effectively measure and evaluate hemodynamic parameters in patients that have been subjected to stressful conditions such as the hemodialysis session. The method ensured that the stress levels during the dialysis session were minimized and reduced thereby altering the blood flow in the thoracic cavity. Albert et al  note the use of bioimpedance cardiography also provided an analysis of waveforms that would be used to estimate the intravascular volume status of the patients that were under the hemodialysis session.
- C.T. Leondes, Biomechanical systems technology, Hackensack, NJ: World Scientific Publishing Limited, 2007.
- A. Feldman, Heart failure: device management, West Sussex, UK: Blackwell Publishing Ltd, 2010.
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- S.A. Kamath, M.H. Drazner, G. Tasissa, J.G. Rogers, L.W. Stevenson and C.W. Yancy, “Correlation of impedance cardiography with invasive hemodynamic measurements in patients with advanced heart failure: the bioimpedance cardiography (BIG) substudy of the ESCAPE trial,” in American Heart Journal, Vol. 158, No.2, pp 217-223, 2009.
- N.M. Albert, M.D. Hail, J. Li and J.B. Young, “Equivalence of bioimpedance and thermodilution methods in measuring cardiac outputs in hospitalized patients with advanced chronic heart failure,” in American Journal of Critical Care, Vol. 13, No.6, pp 469-479, 2004.