Cardiac output calculation

Temporal analysis is used for bolus tracking (time-density quantification), functional maps of local perfusion parameters (of heart and brain), contrast-enhanced MRI of the breast, cardiac output calculations by measuring the volume of the left ventricle over time, multiple sclerosis lesion growth / shrinkage over time, regional cardiac wall thickness variations and local stress/strain calculations, and in fluoroscopy, e.g. the freezing of the stent in the video by cancellation of the motion of the coronary vessel. 

Pulmonary artery catheter An invasive device used to measure hemodynamic parameters directly, including cardiac output and pulmonary artery occlusion pressure calculated parameters include stroke volume and systemic vascular resistance. 

The size of the body is another factor that determines cardiac output. Healthy young men have a cardiac output of about 5.5 to 6.0 1/min the cardiac output in women averages 4.5 to 5.0 1/min. This difference does not involve gender per se, but rather the mass of body tissue that must be perfused with blood. Cardiac index normalizes cardiac output for body size and is calculated by the cardiac output per square meter of body surface... 

This observation is used to calculate cardiac output by using a suitable marker substance such as oxygen, heat or dye and the following equation ... 

A marker substance is injected into a central vein. A peripheral arterial line is used to measure the amount of the substance in the arterial system. A graph of concentration versus time is produced and patented algorithms based on the Stewart-Hamilton equation (below) are used to calculate the cardiac output. 

The semi-log transformation again makes the rise and fall of the graph linear. Note that this time there is no recirculation hump. As the fall on the initial plot was exponential, so the curve is transformed to a linear fall by plotting it as a semi-log. The AUC is still used in the calculations of cardiac output. 

Cardiac output can be measured using dye- or thermal-dilution techniques or by placement of an electromagnetic flow probe around the pulmonary artery. Insertion of a pressure transducer or fluid-filled catheter into the pulmonary artery and pulmonary vein allows for the calculation of pulmonary vascular resistance. The measurement of flow through the proximal aorta may also be useful but does not include coronary blood flow and as such is not equivalent to... 

This reference blood sample is used to calculate the cardiac output by the formula ... 

Circulatory parameters The determination of circulatory parameters allows a rough calculation of the amount of blood already lost as well as optimizing the subsequent diagnostic and therapeutic measures. Loss of more than 800-900 ml blood (or less in older patients and in cases of anaemia) causes circulatory symptoms tachycardia, fall in blood pressure, decrease in both cardiac output and venous return to the heart. A central venous pressure (CVP) of < 5 cm H2O suggests an unfavourable prognosis. The Allgoewer-Burri index has proved to be a useful, objective parameter ... 

Invasive hemodynamic monitoring usually is performed with a flow-directed pulmonary artery (PA) or Swan-Ganz catheter placed percutaneously through a central vein and advanced through the right side of the heart and into the PA. Inflation of a balloon proximal to the end port allows the catheter to wedge, yielding the PAOP, which estimates the pulmonary venous (left atrial) pressure and, in the absence of intracardiac shunt or mitral valve or pulmonary disease, left ventricular diastolic pressure. Additionally, cardiac output may be measured and systemic vascular resistance (SVR) calculated. Normal values for hemodynamic parameters are listed in Table 14—12. 

Qrms = root mean square systolic or diastolic flow rate, cm /s Ap = mean systolic or diastolic pressure drop, mmHg In vitro regurgitation volume (RV) data in the bio-medical engineering literature is generally poorly reported. Only RV data expressed in cm /stroke or data that could be calculated (from the information provided) into such a form were used. In many instances, RV would be expressed in the literature as a percentage, with no information on cardiac output and/or heart rate. The work of Dellsperger et al., (16) and in our laboratory tend to indicate that for a given valve, at a fixed heart rate the value of RV in cm /stroke does not vary (except within experimental error) with cardiac output. 

If the above measures are unsuccessful, insert a central venous pressure (CVP) monitor or pulmonary artery catheter to detenaine whether further fluids are needed and to measure the cardiac output (CO) and calculate the systemic vascular resistance (SVR) as follows ... 

To illustrate how a thermo dilution curve is processed, cardiac output is calculated below using the dilution curve shown in Figure 13.2. 

Stephen Hales, an English clergyman and physicist, carried out a classic experiment in 1732 to determine blood pressure. He connected a U tube to the carotid artery of a mare and observed the height that blood rose in the tube. Then, using fluid dynamic principles, he calculated the velocity of blood in the aorta, force of contraction, and stroke volume. This work has been the foundation of modem hemodynamics and was used by Bernoulli in his quite accurate calculation of cardiac output in 1737. 

Bazett, H.C., Cotton, F.S., Laplace, L.B. et al. (1935) The calculation of cardiac output and effective peripheral resistance from blood pressure measurements with an appendix on the size of the aorta in man. Am. J. Physiol, 113,312-334. 

The calculated dependence of the LV ejection parameters, and the oxygen consumption on the heart rate are presented in Table 1. As seen, the increase in heart rate is associated with an increase in the cardiac output, and the... 

Eq. (5) and (6) can be incorporated into the general model discussed here and solved for different values ofA. Table 5 lists the calculated mechanical parameters for different valvular stenosis. Interestingly, the ejection fraction and cardiac output does not change until a critical stenosis is reached. A decrease in the peak flow with increased stenosis is followed by a longer ejection time so as to maintain a constant ejection fraction. The ejection fraction sharply declines once... 

Upon stabilization, placement of a pulmonary artery (PA) catheter may be indicated based on the need for more extensive cardiovascular monitoring than is available from non-invasive measurements such as vital signs, cardiac rhythm, and urine output.9,10 Key measured parameters that can be obtained from a PA catheter are the pulmonary artery occlusion pressure, which is a measure of preload, and CO. From these values and simultaneous measurement of HR and blood pressure (BP), one can calculate the left ventricular SV and SVR.10 Placement of a PA catheter should be reserved for patients at high risk of death due to the severity of shock or preexisting medical conditions such as heart failure.11 Use of PA catheters in broad populations of critically ill patients is somewhat controversial because clinical trials have not shown consistent benefits with their use.12-14 However, critically ill patients with a high severity of illness may have improved outcomes from PA catheter placement. It is not clear why this was... 

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