Measuring Stroke Volume: Techniques And Understanding

how do you get stroke volume

Stroke volume is a metric used to assess cardiac function. It refers to the volume of blood pumped by the heart with each contraction. This metric is a key indicator of health and efficiency. To calculate stroke volume, you need to know the cardiac output and heart rate. The formula is: Stroke Volume = Cardiac Output / Heart Rate. The regular values of stroke volume are between 60 and 120 mL per beat.

Characteristics Values
Definition Volume of blood pumped by the heart with each contraction
Calculation End-Diastolic Volume (EDV) - End-Systolic Volume (ESV)
Average Value 70ml for a 70kg male
Normal Range 50-100ml
Regular Values 60-120ml per beat
Training 120ml
Athlete 200ml

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End-diastolic volume (EDV)

EDV is a crucial factor in determining stroke volume, which is the volume of blood pumped out of the heart's left ventricle during each systolic contraction. The average stroke volume of a 70 kg male is 70 mL, and this can be calculated by subtracting the end-systolic volume (ESV) from the EDV. ESV refers to the volume of blood remaining in the ventricle after contraction.

The calculation of stroke volume is essential in clinical settings for diagnosing and monitoring various cardiac conditions, such as organ failure, valvular diseases, and cardiomyopathies. It also plays a vital role in treatment evaluation and decision-making.

EDV can be measured using non-invasive procedures like echocardiography, which uses ultrasound technology to visualise the heart's structure and blood flow. Alternatively, more invasive methods such as cardiac catheterization can be employed, where a thin, flexible tube is inserted into the heart to directly measure pressures and volumes.

The normal range for EDV is approximately 130 mL, and it can vary depending on age, gender, and other individual factors. Understanding EDV is crucial in assessing cardiac function and guiding treatment strategies.

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End-systolic volume (ESV)

ESV can be determined using various techniques such as gated SPECT imaging and cardiac MRI, which employs a combination of semi-automated feature recognition and manual contour correction based on Simpson's method ("summation of disks"). The accuracy and reproducibility of ESV measurements are generally high, making it a valuable tool in assessing cardiac function.

The calculation of ESV involves measuring the ventricular cross-sectional areas determined by the endocardial contours at the end of the systolic ejection phase. This is done by selecting images with the smallest blood volume, accounting for slice thickness and gap. The end-systolic volume index (ESVI) is then calculated by correcting the ESV for the body surface area (BSA) using the formula: ESVI = ESV/BSA [mL/m2].

Normal values for ESV differ for the left and right ventricles depending on gender, age, and the imaging modality used. Values above the normal range may indicate systolic dysfunction. For example, in women aged 16-83 years, the normal range for ESVI is 10-38 mL/m2, while for women aged 20-83 years, the range is 13-48 mL/m2.

ESV plays a crucial role in understanding and managing various cardiovascular conditions. For instance, in acute mitral regurgitation, ESV may be normal or decreased, while in chronic mitral regurgitation, it is typically normal. Additionally, changes in ESV can provide insights into cardiac function during exercise. An increase in ESV after exercise has been found to independently predict mortality in patients with coronary heart disease.

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Cardiac output calculation

Stroke volume is a crucial indicator of health and efficiency, and its calculation is an essential metric in assessing cardiac function. Cardiac output is a related metric that refers to the volume of blood pumped by the heart through the systemic circulation over a given period, typically measured in litres per minute.

The calculation of cardiac output involves several variables and methods. One of the more conventional approaches to calculating cardiac output is by multiplying the heart rate by the stroke volume.

The Fick Principle, applied to cardiac output, utilises the understanding that the total uptake of oxygen by peripheral tissues is equal to the product of blood flow to those tissues and the arterial-venous oxygen concentration difference. Thus, the formula for calculating cardiac output using this method is:

> Cardiac output = Oxygen consumption / Arteriovenous oxygen gradient

The normal range for cardiac output is 4-8 L/min, and this value is influenced by cardiac output decreasing during events such as acute myocardial infarction.

Additionally, stroke volume may be calculated as the difference between the end-diastolic volume and the end-systolic volume. This value is then multiplied by the heart rate to determine cardiac output.

In conclusion, the calculation of cardiac output is a multifaceted process that involves a range of physiological parameters and medical imaging techniques.

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Medical imaging techniques

Medical imaging plays a vital role in the diagnosis and treatment of strokes. The type of stroke, whether it is ischemic or hemorrhagic, determines the course of treatment. Therefore, the first step in evaluating a stroke patient is to determine the type of stroke. This is done through medical imaging techniques such as:

  • Computed Tomography (CT): CT scanning combines special X-ray equipment with sophisticated computers to produce multiple images of the inside of the body. CT of the head can detect a stroke from a blood clot or bleeding within the brain. CT angiography (CTA) and CT perfusion (CTP) can also be performed to improve the detection and characterization of stroke. In CTA, a contrast material is injected intravenously, and images are obtained of the cerebral blood vessels. CTP involves rapidly injecting a contrast material and repeatedly imaging the brain to assess blood flow.
  • Magnetic Resonance Imaging (MRI): MRI uses a powerful magnetic field, radio frequency pulses, and a computer to produce detailed images of the brain. MR angiography (MRA) is a procedure that uses MRI to image the cerebral vessels. MR perfusion (MRP) produces images of blood flow.

These medical imaging techniques help physicians decide on the best therapy for a patient experiencing a stroke.

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Clinical diagnosis

Stroke volume is a crucial metric in clinical diagnosis, providing valuable insights into cardiac function and aiding in the assessment of cardiac output. It is defined as the volume of blood pumped out of the heart's left ventricle during each systolic cardiac contraction. The calculation of stroke volume involves subtracting the end-systolic volume (ESV) from the end-diastolic volume (EDV). This value is essential for understanding cardiac health and efficiency.

In a clinical setting, stroke volume can be determined through various methods, including:

  • Echocardiography: This technique utilizes ultrasound to visualize the heart's structure and measure blood flow. It allows for the assessment of EDV and ESV, from which stroke volume can be derived. Echocardiography is non-invasive and is often used to calculate stroke volume.
  • Cardiac Catheterization: This invasive procedure involves inserting a catheter into the heart chambers to directly measure pressures and volumes. It provides an accurate determination of EDV and ESV.
  • Thermodilution Technique: This method involves injecting a cold solution into a central vein and measuring the temperature changes as blood mixes in the pulmonary artery. It is commonly used in intensive care settings.
  • Doppler Techniques: Doppler ultrasound measures blood flow velocities and, in combination with vessel cross-sectional area, can assess stroke volume.
  • Impedance Cardiography: This technique measures changes in electrical impedance across the chest with each heartbeat, which correlates with changes in stroke volume.

The clinical diagnosis of stroke volume plays a vital role in several aspects:

  • Diagnosing Cardiac Conditions: By assessing stroke volume, healthcare professionals can identify cardiac conditions such as organ failure, valvular diseases, and cardiomyopathies.
  • Monitoring Patient Health: Stroke volume monitoring is crucial for critically ill hypovolemic patients. It helps assess cardiac pump function and organ perfusion.
  • Guiding Treatment Tactics: Understanding stroke volume is essential for optimizing treatment plans. For example, in patients with speech difficulties after a stroke, knowledge of stroke volume can guide medication regimens, surgical interventions, and lifestyle modifications.
  • Prognostic Value: Measurements of stroke volume provide valuable prognostic information, helping predict outcomes and guide therapeutic decisions.
  • Research and Development: Accurate stroke volume calculation is indispensable for research endeavours, facilitating a better understanding of disease mechanisms, evaluating new therapies, and developing innovative diagnostic and treatment approaches.

Frequently asked questions

Stroke volume is the amount of blood pumped by the heart in every beat. Each time the left ventricle contracts, it pushes blood from the heart to the aorta and toward the rest of the body.

Stroke volume is calculated by dividing cardiac output by heart rate.

A healthy adult will typically have a stroke volume between 50-100 mL.

Yes, stroke volume can be measured non-invasively using echocardiography, Doppler ultrasound, or impedance cardiography.

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