Which of the following statements is false?
A. Cardiac output is equal to total capillary flow
B. Increased HR increases SV and CO
C. Increased EDV increases SV
D. Increased preload increases SV
E. Decreased ESV increases SV
Answer (1)
Analyzes each statement related to cardiac physiology.
Identifies that increased HR does not always increase SV, especially at very high heart rates.
Concludes that the statement 'Increased HR increases SV and CO' is false.
Explains the relationship between HR, SV, and CO in the context of exercise physiology.
Explanation
Analyze Each Statement Let's analyze each statement to determine which one is false.
Statement 1: Cardiac output is equal to total capillary flow
Cardiac output (CO) is the amount of blood pumped by the heart per minute. Total capillary flow refers to the sum of blood flow through all capillaries in the body. While related, they are not necessarily equal. CO represents the initial output from the heart, which then distributes into the capillary beds. This statement is potentially false.
Statement 2: Increased HR increases SV and CO
Heart rate (HR) is the number of heartbeats per minute. Stroke volume (SV) is the amount of blood ejected by the heart with each beat. Cardiac output (CO) is the product of HR and SV (CO = HR x SV). While increasing HR can increase CO, it doesn't always increase SV. In fact, very high HR can decrease SV due to reduced filling time. This statement is potentially false.
Statement 3: Increased EDV increases SV
End-diastolic volume (EDV) is the volume of blood in the ventricles at the end of diastole (filling). According to the Frank-Starling mechanism, increased EDV (preload) leads to increased SV. This statement is generally true.
Statement 4: Increased preload increases SV
Preload is the volume of blood in the ventricles at the end of diastole, which is essentially the EDV. As stated in statement 3, increased preload increases SV due to the Frank-Starling mechanism. This statement is generally true.
Statement 5: Decreased ESV increases SV
End-systolic volume (ESV) is the volume of blood remaining in the ventricles at the end of systole (contraction). Stroke volume (SV) is the difference between EDV and ESV (SV = EDV - ESV). Therefore, if ESV decreases, SV increases, assuming EDV remains constant. This statement is generally true.
Based on this analysis, statements 1 and 2 are potentially false. However, statement 2 is more likely to be false because increased HR does not always increase SV, especially at very high heart rates. Statement 1 is generally considered true in a broad sense, assuming all blood pumped by the heart eventually flows through the capillaries. Therefore, statement 2 is the most likely false statement.
Identify the False Statement The most likely false statement is: Increased HR increases SV and CO. While increased HR can increase CO, it does not necessarily increase SV. At very high heart rates, the filling time is reduced, which can decrease SV. Therefore, the statement is not universally true.
Conclusion The false statement is that increased HR increases SV and CO.
Examples
Understanding the relationship between heart rate, stroke volume, and cardiac output is crucial in exercise physiology. For example, during intense exercise, heart rate increases to deliver more oxygen to the muscles. However, if the heart rate becomes too high, the stroke volume may decrease, limiting the increase in cardiac output and potentially affecting performance. This knowledge helps athletes and trainers optimize training regimens to maximize cardiovascular efficiency.
