Measurements of cardiac efficiency and internal work of the left ventricle via reconstructed impedance cardiography.

Objective. The aim of this study was to investigate methods for measuring the cardiac efficiency (CE) and internal work (IW) of the left ventricle via reconstructed impedance cardiography (RICG).Approach.On the basis of the physiological context and Bernoulli's equation in physics, methods of measuring the CE and IW were proposed. The CE, IW, internal work index (IWI), and other data from 180 healthy adults and 144 patients with cardiovascular disease were measured.Main results. The CE of 180 healthy adults was 22.5 ± 2.2%, and the IWI was 22.3 ± 5.2 J l-1m-2. CE decreased with age, and the CE of the younger group (23.5 ± 1.9%) was larger than that of the older group (21.5 ± 1.9%),P < 0.01. The IWI increased with age, and the IWI of the younger group (19.0 ± 3.8 J l-1m-2) was smaller than that of the older group (24.8 ± 4.3 J l-1m-2),P < 0.01. There were no significant difference in CE (22.4 ± 2.2% and 22.6 ± 2.2%) or in the IWI (21.9 ± 5.1 J l-1m-2and 22.6 ± 5.2 J l-1m-2) between the male and female groups. The CEs and IWIs of patients with hypertension, coronary heart disease, and heart failure were 17.4 ± 2.4% and 41.8 ± 15.6 J l-1m-2, 17.6 ± 3.0% and 35.1 ± 10.4 J l-1m-2, and 15.8 ± 3.5% and 42.1 ± 15.6 J l-1m-2, respectively. These CEs were all smaller than that (21.6 ± 2.0%) of the healthy contrast groupP < 0.01, while the IWIs were all larger than that (24.6 ± 4.8 J l-1m-2) of the healthy contrast group,P < 0.01.Significance.The CEs and IWIs measured in this study may reflect physiological changes in healthy humans and pathogenic conditions in patients with cardiovascular disease.

Waveform analysis of differential graphs of reconstructed impedance cardiography from healthy individuals.

PURPOSE: The aim is to measure and analyze the wave amplitudes and time intervals of differential graphs of reconstructed impedance cardiography (RICG). METHODS: 180 adults with normal cardiac function between the ages of 18-78 were included in the study. Six mingled impedance changes on chest surface were simultaneously detected for each subject. The differential graphs of five impedance change components of RICG were obtained through waveform separation and software differentiation. The amplitudes of C, X, O, b waves and time intervals of Q-b and Q-C were measured and statistically analyzed. RESULTS: The amplitudes of C and X waves in PL, PR, AO, and that of C, O, b waves in LV and RV, all decrease as age increases. Wave amplitudes of the female group were bigger than those of the male group (p < .01), while the Q-C intervals of the female group were shorter than that of the male group (p < .01). Among five impedance change components, the wave amplitude of AO was larger than those of PL and PR (p < .01), and wave amplitudes of PL and PR were bigger than those of LV and RV (p < .01). Q-C intervals of LV and RV were longer than those of AO, PL and PR (p < .01), while the Q-b intervals of LV and RV were shorter than the Q-C intervals of AO, PL, and PR. CONCLUSIONS: The differential graphs of RICG could reflect indirectly the physiological activities and pathological changes of the heart and of the large blood vessels in thorax.

Comparing square root method of measuring the cardiac output by means of aortic impedance change component to Kubicek's method.

PURPOSE: The aim of this study is to explore a calculated method used to measure the cardiac output using the aortic impedance change component of reconstructed impedance cardiography. METHODS: Routine impedance cardiography was measured using Kubicek's method with four ring electrodes. The thoracic mixed impedance changes were measured by six leads, which consisted of 15 electrodes. The aortic impedance change component was separated from six thoracic mixed impedance changes through waveform reconstruction. The square root formula used to calculate the cardiac output was deduced based on the thoracic impedance change equation and the aortic volume change hypothesis during the systole period. The cardiac outputs of 180 normal adults and 72 patients with cardiac insufficiency who could still walk freely were contrastively computed with both Kubicek's formula and the square root formula. RESULTS: For 180 normal adults, the cardiac index (CI) computed with the square root formula was 3.60 ± 0.45 L/min/m2 , with normal values ranging from 2.7 to 4.5 L/min/m2 . A total of 163 cases (90.6%) had a CI in the standard range (2.7-4.3 L/min/m2 ) adopted in clinical applications. The CI computed with Kubicek's formula was 3.61 ± 0.86 L/min/m2 , with normal values ranging from 1.9 to 5.3 L/min/m2 , and only 115 cases (63.9%) had a CI in the above standard range. Among the 72 patients with cardiac insufficiency, 20 (27.8%) patients had a CI < 2.0 L/min/m2 with Kubicek's formula. Of these 20 cases, 9 cases had a CI < 1.5 L/min/m2 , and 4 cases had a CI < 1.1 L/min/m2 . In contrast, none of the 72 patients had a CI < 2.0 L/min/m2 with the square root formula. In addition, the influence of the chest circumference on the CI was lower for the square root formula than for Kubicek's formula. CONCLUSIONS: The CI calculated with the square root formula had a better normal value range, was more accurate for the patients with cardiac insufficiency, and was less affected by the chest circumference than the CI calculated with Kubicek's formula.

Analyzing the formation of normal and abnormal O waves in thoracic impedance graph using the impedance change components for aorta, blood vessels in lung and ventricles.

BACKGROUND: Many measurements of thoracic impedance graph show that the small C wave and big O wave appear often for patients with cardiac insufficiency, and the O/C ratio is bigger. And for the normal body, especially a younger one, the bigger O wave may also appear. But since the amplitude of the C wave of a normal body is bigger, the O/C ratio is smaller. The aim of the present paper is to investigate the formation mechanism of the normal and abnormal O waves in thoracic impedance graph. METHODS AND RESULTS: The thoracic mixed impedance changes are measured with 6 leads consisting of 15 electrodes. The impedance change components for the aorta (AO), blood vessel in left lung (PL), blood vessel in right lung (PR), left ventricle (LV) and right ventricle (RV) are separated from thoracic mixed impedance changes by means of establishing and solving the thoracic impedance equations. The amplitudes of the O and C waves of various impedance change components are measured for 50 normal healthy adults and 34 patients with cardiac insufficiency. The formation mechanism of normal and abnormal O waves in thoracic impedance graph is analyzed using the superposition of the O waves of the above impedance change components. Detection subjects are 50 healthy adults and 34 hospital patients with cardiac insufficiency. (1) Thoracic impedance graph: The O/C ratios of the normal group are significantly smaller than that of the abnormal group, p < 0.001. The O wave of first lead (E1-E1') is significantly bigger than that of leads 4 and 5 (E4-E4' and E5-E5') in the normal group, p < 0.001. (2) The impedance change component: The O waves of the AO, PL, and PR are significantly smaller than that of the LV and RV in the normal group, p < 0.001. The O wave and O/C of the AO, PL and PR of normal group are significantly smaller than that of the abnormal group, p < 0.001. CONCLUSIONS: The O wave of the thoracic impedance graph is formed due to the superposition of the O waves of the impedance change components for the aorta, blood vessels in lung and ventricles.

Studies on separating the impedance change components of blood vessels and ventricles in thorax from mixed impedance signals on chest surface.

PURPOSE: The aim of the present study is to separate the impedance change components of the blood vessels and ventricles in thorax from the mixed impedance signals detected on the chest surface. METHODS: The mixed impedance signals on the chest surface are measured with a 15 electrode lead system. The thoracic impedance equations are established and solved iteratively with the algebraic reconstructed technique. Experiments were performed on 80 healthy, otherwise normal, adults. RESULTS: Five impedance change components for the aorta (AO), blood vessel in left lung (PL), blood vessel in right lung (PR), left ventricle (LV), and right ventricle (RV) are separated from the mixed impedance signals. The experiments show that the main waveform of the ventricular components LV and RV is contrary to that of the vascular components AO, PL, and PR, and the negative peak point of the waveform graphs of LV and RV are in phase with the second cardiac sound (S2). The waveform graphs of various components correspond with the physiological activities of the heart and blood vessels in a cardiac cycle. The statistical results for 80 normal adults show that the amplitude of AO is the largest and that of PL and PR is the next, while that of LV and RV is the smallest. There are significant differences between them (P < 0.01). CONCLUSIONS: The mathematical model and the measurement method for the separation in the present paper are feasible.

Mechanism of the formation for thoracic impedance change.

The purpose of this study is to investigate the mechanism of the formation for thoracic impedance change. On the basis of Ohm's law and the electrical field distribution in the cylindrical volume conductor, the formula about the thoracic impedance change are deduced, and they are demonstrated with the model experiment. The results indicate that the thoracic impedance change caused by single blood vessel is directly proportional to the ratio of the impedance change to the basal impedance of the blood vessel itself, to the length of the blood vessel appearing between the current electrodes, and to the basal impedance between two detective electrodes on the chest surface, while it is inversely proportional to the distance between the blood vessel and the line joining two detective electrodes. The thoracic impedance change caused by multiple blood vessels together is equal to the algebraic addition of all thoracic impedance changes resulting from the individual blood vessels. That is, the impedance changes obey the principle of adding scalars in the measurement of the electrical impedance graph. The present study can offer the theoretical basis for the waveform reconstruction of Impedance cardiography (ICG).