Critically ill patients in a cardiovascular intensive care unit must be intensely monitored for any number of conditions. One of these conditions is hypoperfusion, which is an overall decrease in blood flow throughout the body. Low stroke volume is one indicator of hypoperfusion. The pressure-volume (PV) graph below shows three possible loops for the heart. The control loop shows a healthy heart while the other two loops show reduced or increased preload (assuming that afterload and contractility remain fixed). 200 LV Pressure (mmHg) 100- 0 Preload Control ↑ Preload 0 100 LV Volume (ml) (a) What is the stroke volume for the control patient? RK 15 200 (b) A healthy heart rate (HR) is measured as 82 beats per minute. What is the control patient's cardiac output CO? Control patient's CO: mL min (c) Using the control PV loop, estimate the work done by the heart (in J) for a healthy individual during a single heart beat. Select the answer that is closest to your estimate. Hint: What are the units of work? What are the units of the PV loop? Assume the PV loop as roughly a rectangle, with the height of the rectangle 75 mmHg, and the width of the rectangle 75 ml. (d) If a patient is suffering from hypoperfusion, which of the above graphs best represents their PV Loop?

Critically ill patients in a cardiovascular intensive care unit must be intensely monitored for any number of conditions. One of these conditions is hypoperfusion, which is an overall decrease in blood flow throughout the body. Low stroke volume is one indicator of hypoperfusion. The pressure-volume (PV) graph below shows three possible loops for the heart. The control loop shows a healthy heart while the other two loops show reduced or increased preload (assuming that afterload and contractility remain fixed). 200 LV Pressure (mmHg) 100- 0 Preload Control ↑ Preload 0 100 LV Volume (ml) (a) What is the stroke volume for the control patient? RK 15 200 (b) A healthy heart rate (HR) is measured as 82 beats per minute. What is the control patient's cardiac output CO? Control patient's CO: mL min (c) Using the control PV loop, estimate the work done by the heart (in J) for a healthy individual during a single heart beat. Select the answer that is closest to your estimate. Hint: What are the units of work? What are the units of the PV loop? Assume the PV loop as roughly a rectangle, with the height of the rectangle 75 mmHg, and the width of the rectangle 75 ml. (d) If a patient is suffering from hypoperfusion, which of the above graphs best represents their PV Loop?