The term cardiac output refers to the amount of blood the heart pumps in one minute. If you suffer from diarrhea, kidney problems, vomiting or bleeding, your cardiac output should be determined. This information helps your doctor determine if you need fluids or are responding well to the rehydration therapy you are on. To calculate cardiac output, you need to know your heart rate and systolic output.
Steps
Part 1 of 3: Calculating the Heart Rate
Step 1. Get a stopwatch or watch
Before measuring your pulse, you must have an accurate instrument that measures the seconds.
- You can try to keep track of the beats and seconds in mind, but it will be a very inaccurate job.
- The ideal thing would be a timer, so you can forget about the time and just focus on counting the beats.
Step 2. Turn your hand palm up
Although there are several points where you can feel the heartbeat, the inside of the wrist is the easiest place to access.
- You can also try to feel the pulse on the jugular area.
- This is located on the side of the neck, near the throat.
Step 3. Find the pulse
Use the middle and index fingers of the other hand, place them on the inside of the wrist or under the jaw line.
- You have to move your fingers a little to find the heartbeat.
- You will also need to apply some pressure.
Step 4. Start counting the beats
When you've found your wrist, start the stopwatch or look at the second hand on your watch. Wait until the hand is at 12 o'clock and start counting the beats.
- Concentration is essential for this task. Count the beats for one minute (until the hand returns to 12 o'clock).
- This value represents the heart rate.
- If you have trouble counting beats for a full minute, count them for 30 seconds (until the hand reaches 6 o'clock) and then multiply the value by 2.
Part 2 of 3: Determine the Systolic Range
Step 1. Get an echocardiogram to determine the size of your heart
This is a specific test that determines the systolic volume.
An echocardiogram uses radio waves to recreate the image of the heart through a computer in order to measure the volume of blood that passes through it
Step 2. Determine the surface of your left ventricle
Without an echocardiogram you are not able to know this value.
This exam offers the possibility of having all the data necessary for subsequent calculations
Step 3. Calculate the area of the outflow tract of the left ventricle (also called LVOT)
This is the portion of the heart that blood passes through to get to the arteries. Use the following equation to determine the area:
- Multiply the square of the left ventricular outflow tract diameter by 3.14.
- Divide the result by 4.
- The result is the area of the outflow tract of the left ventricle.
- 3, 14 x diameter of the LVOT ^ 2.
Step 4. Determine the systolic range
It is calculated by subtracting from the amount of blood in a ventricle at the end of the beat (end-systolic volume, ESV) the amount of blood present in the ventricle before the beat (end-diastolic volume, EDV).
- Systolic range = ESV - EDV
- Although the systolic range refers to the left ventricle, it can also be applied to the right as the value is usually identical.
Step 5. Determine the speed / time integral
This data (VTI) determines the amount of blood flowing through a ventricle.
To determine the speed / time integral of the left ventricle, the doctor who performs the echocardiogram will trace the ventricle
Step 6. Calculate the systolic output index
To do this, take the speed / time integral, which is the amount of blood that is pumped with each beat, and divide it by the area of the left ventricle in square meters.
This formula allows direct analysis of the systolic output for any patient regardless of size
Step 7. Determine Cardiac Output
Finally, to calculate this, multiply the heart rate by the systolic stroke.
- Heart rate x Systolic output = Heart rate.
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For example, if you have a heart rate of 60 beats per minute and your systolic output is 70ml, then your cardiac output is:
60 bpm x 70 mL = 4200 mL / min or 4.2 liters per minute
- If your heart rate, systolic output (or both) increase, cardiac output also increases.
- The systolic range is not subject to large fluctuations except during physical activity and in any case for a minimum value.
- The heart rate increases considerably with physical activity and is the variable that generally causes cardiac output to change.
- The heart rate increases during training because the muscles under stress need more energy.
- The body increases the beat frequency to bring oxygen and nutrients to the body. In fact, the demand for these increases during physical activity.
Part 3 of 3: Understanding the Factors Affecting Cardiac Output
Step 1. Heart rate
It is simply the number of beats the heart makes in one minute. The higher this number, the more blood it pumps throughout the body.
- A normal heart rate usually ranges from 60 to 100 beats per minute.
- When the frequency is lower it is referred to as bradycardia, a condition that involves too little blood in circulation.
- If the heart is beating very fast this is referred to as tachycardia (a rate that is beyond normal limits) or, in severe cases, arrhythmia (problems with the speed or rhythm of the heartbeat).
Step 2. Although a higher rate may be thought to mean more blood circulating, the heart actually pumps less blood with each contraction
Step 3. Contractility
It is the ability of the heart muscle to contract. The heart is made up of a series of muscles whose rhythmic contraction allows blood to pump.
- The stronger the contractions, the more blood circulates.
- This ability is affected when a piece of muscle dies and the heart is able to pump less blood.
Step 4. Preload (venous return)
This term refers to the heart's ability to extend before a contraction.
- According to Starling's law, the strength of a contraction depends on how long the heart muscle has stretched.
- Therefore, the greater the preload, the greater the contraction force resulting in an increase in range.
Step 5. Cardiac afterload
It is simply the effort the heart has to go through to pump blood which depends on the tone of the blood vessels and blood pressure.
