How to find stroke volume
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Methods to Determine Stroke Volume: A Comprehensive Overview
Introduction to Stroke Volume Measurement
Stroke volume (SV) is a critical parameter in assessing cardiac function, representing the volume of blood pumped by the left ventricle of the heart in one contraction. Accurate measurement of SV is essential for diagnosing and managing various cardiovascular conditions. Several methods have been developed to estimate SV, each with its advantages and limitations.
M-Mode and Two-Dimensional Echocardiography
Estimation Using M-Mode Echocardiography
M-mode echocardiography, combined with two-dimensional echocardiography, can be used to estimate SV by measuring the left ventricular (LV) dimensions. This method involves calculating the end-diastolic and end-systolic volumes using regression equations derived from LV dimensions and wall thickness. The study found that this method produced a mean relative error of 0.9% in diastole and 1.4% in systole, making it a reliable approach for clinical and epidemiological applications.
Doppler Echocardiography
Doppler echocardiography measures SV by calculating the time-velocity integral of blood flow at specific cardiac sites, such as the aortic annular plane. The combination of aortic annular cross-sectional area and the leading edge technique for measuring the time-velocity integral provided the most accurate SV measurements, closely correlating with the thermodilution method (r = 0.87).
Pulse-Contour Methods
Pulse-Contour Analysis
The pulse-contour method estimates SV by analyzing the contour of the arterial pressure waveform. This method is advantageous for continuous monitoring of cardiovascular status. However, the correlation coefficients ranged from 0.59 to 0.84, indicating variability in accuracy. Despite its simplicity and rapidity, the pulse-contour method may not accurately detect small changes in SV.
Central Aortic Pressure
Several pulse-contour methods have been evaluated for estimating SV from central aortic pressure. While good correlations were found in controlled conditions, the methods performed poorly under varying hemodynamic conditions, limiting their clinical usefulness.
Non-Invasive Methods
Inverse Problem-Solving Method
A novel non-invasive method involves using a mathematical inverse-problem solving approach to estimate SV from brachial blood pressure and carotid-femoral pulse wave velocity. This method showed a high agreement with MRI-derived SV measurements (r = 0.83), outperforming traditional regression models.
Oxygen Pulse During Exercise
Estimating SV from oxygen pulse (OP) during exercise involves calculating SV using the equation SV = OP/a-vO2D, where a-vO2D is the arterio-venous oxygen difference. This model showed reasonable agreement with impedance cardiography, making it a viable option for healthy populations during exercise.
Radionuclide Techniques
Radionuclide Angiocardiography
Radionuclide techniques, such as multigated equilibrium blood-pool scintigraphy, can determine SV by correcting for attenuation. This method showed a high correlation with thermodilution measurements (r = 0.96), providing a reliable non-invasive means of calculating SV without geometric assumptions.
Conclusion
Various methods are available for estimating stroke volume, each with specific applications and accuracy levels. M-mode and Doppler echocardiography are reliable for clinical use, while pulse-contour methods offer continuous monitoring but with variable accuracy. Non-invasive techniques, such as the inverse problem-solving method and radionuclide angiocardiography, provide promising alternatives for accurate SV measurement. Understanding the strengths and limitations of each method is crucial for selecting the appropriate technique in different clinical scenarios.
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