40 year old man presents with resting heart rate of 180 beats/min. Pressure-volume diagram of left ventricle is shown below. What is the cardiac output?
## **Core Concept**
The question involves understanding the relationship between heart rate, stroke volume, and cardiac output. Cardiac output (CO) is calculated as the product of heart rate (HR) and stroke volume (SV): CO = HR × SV. The pressure-volume diagram of the left ventricle can provide insights into ventricular function and stroke volume.
## **Why the Correct Answer is Right**
Given the resting heart rate of 180 beats/min, which is significantly elevated (normal resting heart rate is approximately 60-100 beats/min), we can infer the patient is likely experiencing tachycardia. Without specific details on stroke volume from the pressure-volume diagram, we rely on understanding the principles. If we assume a normal stroke volume for simplicity (which can vary widely but is approximately 70 mL for a healthy adult), a heart rate of 180 beats/min would significantly increase cardiac output. However, the actual calculation of cardiac output from the provided information isn't straightforward without the stroke volume. Typically, at high heart rates, diastolic filling time decreases, which can decrease stroke volume due to reduced preload.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Without specific cardiac output values provided for each choice, we can't directly assess, but if it's lower than option , it might not adequately reflect the increased cardiac output expected with a heart rate of 180 beats/min.
- **Option B:** Similarly, this would be incorrect if it doesn't accurately reflect the expected cardiac output based on the elevated heart rate and any potential changes in stroke volume.
- **Option D:** This option would be incorrect if it suggests a cardiac output that doesn't correlate with the physiological changes associated with a significantly elevated heart rate.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that cardiac output can increase with heart rate up to a point, but beyond 160-180 beats/min, cardiac output may actually decrease due to decreased diastolic filling time and subsequently reduced stroke volume. This relationship is crucial in understanding tachycardia's effects on cardiac function.
## **Correct Answer:** .