Understanding Blood Volume and Ejection in the Healthy Heart

Understanding how the heart manages blood volume and ejection is crucial for comprehending heart function and health. The end-diastolic volume (EDV) is the amount of blood in the ventricles at the end of the diastolic phase (the filling phase of the cardiac cycle). This is typically about 70 mL per meter squared of body surface area in a normal ventricle. However, during the contraction phase, or ventricular systole, the ventricle releases a portion of this blood, which is known as the stroke volume (SV).

To determine the exact amount of blood released during each contraction, we can use the ejection fraction (EF). The ejection fraction is calculated as the SV divided by the EDV. A typical ejection fraction is around 70%, meaning that if the EDV is 120 mL, the ventricle releases approximately 84 mL during contraction (120 mL x 0.7 84 mL).

For a typical adult heart, the end-diastolic volume (EDV) is 130 mL just before contraction. In a resting state, the heart expels about 70 mL during systole, leaving around 60 mL as the end-systolic volume (ESV). This means that at rest, the heart's ejection fraction is about 54% (70 mL / 130 mL 0.54). However, during heavy exercise, the ejection fraction can rise to 90% or higher.

Pathologic States and Dilated Ventricles

In pathologic states, particularly with dilated ventricles, the EDV may increase, leading to a decreased ejection fraction if the ventricular muscle function is impaired. A reduced ejection fraction means that less blood is expelled with each heartbeat, which can lead to a reduction in cardiac output. Cardiac output is the amount of blood pumped by the heart in one minute, and it is essential for maintaining adequate blood flow to the body.

Implications for Health and Disease

The ejection fraction can be a critical indicator of heart function and disease. In healthy individuals, a ejection fraction above 50% is generally considered normal. Below this threshold, a heart is considered to be hypertrophic, and below 40%, it is classified as dilated cardiomyopathy. These conditions can significantly impair heart function, leading to symptoms such as shortness of breath, fatigue, and edema.

Role of Diastolic and Systolic Function

Both diastolic and systolic function contribute to overall heart health. Diastolic function refers to the heart's ability to fill with blood during its resting phase, while systolic function refers to the heart's ability to contract and pump blood. These processes are interdependent and contribute to the overall efficiency of the heart in managing blood volume and ejection.

Conclusion

Understanding the relationship between end-diastolic volume and ejection volume is fundamental to comprehending heart function. The heart's efficiency in managing blood volume and ejection is a critical indicator of overall cardiac health. Understanding these concepts can aid in the diagnosis and treatment of heart conditions, ensuring that individuals can lead healthy, active lives.