Stroke volume is the amount of blood ejected from the left ventricle of the heart during contraction. It usually measures between 60 and 130 mL/beat in healthy individuals. If stroke volume is excessively depressed, as in cases of massive bleeding, heart failure, or extensive burns, there is not enough blood being pumped into circulation to carry oxygen to the cells. Thus, cells die and organs fail. You can calculate stroke volume using one of two equations.
Use the following equation--Stroke Volume = (Cardiac Output) / (Heart Rate)--if the patient is in intensive care and has a catheter in his neck, chest, or arm that allows continuous hemodynamic monitoring.
Plug in the value for Cardiac Output from the thermodilution method. Cardiac output is the amount of blood pumped into circulation each minute. Thermodilution, a technique commonly done in intensive care, involves injecting a fixed amount of cool dye into the patient through a catheter and measuring the concentration of the dye at predetermined intervals.
Plug in the values to obtain Stroke Volume. A heart rate monitor is standard equipment for intensive care patients and can readily supply the Heart Rate value for the formula.
Use the following equation--Stroke Volume = (End-Diastolic Volume) – (End-Systolic Volume)--if the patient is undergoing a left-ventricular angiogram. Left-ventricular angiogram produces an image of the heart chamber through X-ray. A catheter is inserted into the patient’s blood vessel through his groin or arm, and a dye is injected to allow visualization of the heart chamber during the X-ray.
Obtain values for End-Diastolic Volume and End-Systolic Volume, which are provided by the physician after the angiogram is done. When the left ventricle of the heart fills with blood, it contracts, sending blood to other parts of the body. End-Diastolic Volume is the amount of blood in the left ventricle before contraction, and End-Systolic Volume is the residual amount in the chamber after contraction.
Plug in the values to obtain Stroke Volume.
Checking stroke volume requires invasive technique. It is indicated for people who are hemodynamically unstable--like those with massive blood loss or fluid shifts from bleeding or burns--whose status could drastically change from one moment to the next. Some exercise manuals offer equations for stroke volume. They are only estimates. The equations are not accurate and should not be used for patients in the clinical setting. It is unnecessary to derive the exact value for stroke volume for a healthy individual who wants to improve his physique.