Pressure-Volume loop of cardiac cycle is shown below. What does point C represent?
**Core Concept**
The pressure-volume (PV) loop is a graphical representation of the cardiac cycle, illustrating the relationship between ventricular pressure and volume. It provides valuable information about cardiac function, including contractility, preload, and afterload.
**Why the Correct Answer is Right**
Point C in the PV loop represents the end of diastole and the beginning of isovolumetric contraction. At this point, the ventricular pressure has increased to the point where the mitral and tricuspid valves are closed, and the aortic and pulmonary valves are still closed. The ventricle is contracting, but the volume remains constant because the valves are closed. This is a critical point in the cardiac cycle, as it marks the transition from diastole to systole.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because point A represents the end of isovolumetric contraction and the beginning of ventricular ejection. The valves are still closed, but the ventricle is now ejecting blood into the aorta and pulmonary artery.
**Option B:** This option is incorrect because point B represents the end of ventricular ejection and the beginning of isovolumetric relaxation. The ventricle has ejected all its blood, and the valves are closed as the ventricle relaxes.
**Option D:** This option is incorrect because point D is not a valid point in the PV loop. The PV loop typically starts at the origin (0, 0) and moves counterclockwise, representing the cardiac cycle.
**Clinical Pearl / High-Yield Fact**
When interpreting the PV loop, it's essential to understand the relationship between contractility and the slope of the systolic phase. A steeper slope indicates increased contractility, while a flatter slope suggests decreased contractility.
**Correct Answer:** C.