Stroke volume and stroke volume index are important indicators of the heart's condition. Stroke volume measures the quantity of blood that leaves the heart when it beats. Medical professionals determine stroke volume index by factoring the patient's body size into his stroke volume. Stroke volume index is a more precise, individualised measurement. Doctors and nurses use stroke volume and stroke volume index to make assessments about the health of a patient's heart.
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Stroke volume and stroke volume index provide an early warning system for dangerous conditions in the body. The "Critical Care Nursing Textbook" states, "Stroke volume or index thus becomes the single most important piece of information regarding cardiac function..." The volume of blood the heart pumps out is essential to transport oxygen and nutrients throughout the body. In healthy adults, stroke volume changes according to activities, such as changing from a sitting or lying down position to standing upright. A heart rate increase will generally cause stroke volume to increase. For example, anxiety and excitement can increase the stroke volume by 50 to 100 per cent, while exercise might increase it fivefold. Measurement of stroke volume is an important way to evaluate how well the heart is delivering oxygen to the body's organs and tissues. Abnormalities in stroke volume can indicate inadequate circulation or heart failure.
A normal stroke volume is 60 to 100ml/beat. A normal stroke volume index is 33 to 47ml/beat/m2. A low stroke volume index indicates the blood supply to the body is inadequate. If untreated, a low stroke volume index will lead to life-threatening conditions. By combining the stroke volume measurement with oxygen consumption, doctors determine if a patient's stroke volume is adequate to sustain continued health.
Stroke Volume Changes
When stroke volume increases, it might be due to an increase in the force of the heart muscle or an increase in the volume of circulating blood. When stroke volume decreases, it might indicate heart valve dysfunction or impaired heart contractions, both of which could lead to heart failure. A stroke volume that falls below 50ml requires immediate medical intervention.
Stroke Volume Index Changes
When stroke volume index increases, it can be due to several factors. Certain medications, like dobutamine, digitalis or dopamine, can cause an increase in stroke volume index. An increase in stroke volume index could indicate a rise in blood volume, a sharp rise in internal body temperature or the early stage of septic shock. When stroke volume index decreases, it might be due to beta-blocker drugs, or it could indicate a heart attack, congestive heart failure or the late stage of septic shock. A stroke volume index below 25ml requires immediate medical intervention.
There are non-invasive and invasive methods for determining stroke volume. A doctor will use invasive methods in the case of sepsis, hypovolemic shock or to evaluate cardiac output in high-risk surgeries and complex medical situations. Non-invasive methods include electric impedance tomography and echocardiography systems. If your doctor determines that evaluating your stroke volume and stroke volume index is important, she will explain the procedure to you.
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- "Basic Cardiovascular Physiology", University of Virginia School of Medicine Basic Cardiovascular Physiology, University of Virginia School of Medicine
- "Critical Care Nursing Certification"; Thomas Ahrens, Donna Prentice, Ruth M. Kleinpell; 2007; pps 49, 50; Table 5-3: "Determinants of Stroke Volume", page 50