What is the stroke volume of blood in a healthy individual's cardiac cycle?

Question

Accepted Answer

The correct option is 1:
The correct option is 1: 70 ml. This figure represents the typical average **Stroke Volume (SV)** for a healthy adult at rest. The stroke volume is fundamentally defined as the amount of blood ejected by each ventricle—the primary pumping chambers of the heart—in a single contraction, or during one cardiac cycle. In a resting individual, the end-diastolic volume (the volume of blood in the ventricle just before contraction) is typically around 120 ml, and the end-systolic volume (the volume remaining after contraction) is about 50 ml. Therefore, the difference, which is the ejected volume (SV), is approximately 120 ml - 50 ml = 70 ml. This volume is critical because when multiplied by the Heart Rate (HR), it determines the **Cardiac Output (CO)**, which is the total volume of blood pumped by the heart per minute to efficiently supply the body's tissues.

The incorrect option is 2:
The option 5000 ml is incorrect because it is approximately the value for the total **Cardiac Output (CO)** in a resting adult, not the stroke volume ejected in a single beat. Cardiac output is calculated as Stroke Volume multiplied by Heart Rate (CO = SV x HR). Using the correct stroke volume of 70 ml and an average resting heart rate of about 70-72 beats per minute, the product is approximately 4900 to 5040 ml per minute, which is equivalent to 5 liters or 5000 ml. This calculation clearly shows that 5000 ml represents the blood pumped per *minute* (CO), not the blood pumped per *beat* (SV), making it physiologically incorrect for the stroke volume.

The incorrect option is 3:
The value 4 lit (4 liters), which is equivalent to 4000 ml, is physiologically incorrect for the stroke volume under any normal conditions. This extremely large volume would be impossible for the heart to eject in a single contraction and would vastly exceed the capacity of a healthy ventricle, leading to immediate cardiac failure. Even the absolute maximum stroke volume achieved by a highly trained endurance athlete during peak exercise is generally less than 200 ml. Furthermore, 4 liters is a measure that is nearly the total blood volume of an entire human body, reinforcing that this value is far outside the practical range for stroke volume.

The incorrect option is 4:
The value 50 ml is a poor choice for the representative stroke volume, even though it falls within a physiological range. While 50 ml may be the stroke volume for a very small adult, or represent a low-normal output, the generally accepted, teaching standard for a healthy, average adult at rest is 70 ml. Moreover, 50 ml is a value that is actually closer to the **End-Systolic Volume (ESV)**, which is the amount of blood that is *left behind* in the ventricle after contraction, rather than the amount ejected. Therefore, 70 ml is the most accurate and widely used reference figure.