Car 3 - Cardiac Output Flashcards
What is Cardiac output (CO)? What is the equation?
Volume of blood pumped in 1 min. CO = Stroke volume (SV) x HR.
What is Stroke volume (SV)? What is the equation for it?
It is the amount of blood pumped in every heart beat. SV = (End-diastolic volume EDV) - (End-systolic volume ESV).
What is the Fick Principle?
CO = (Rate of O2 consumption)/(Arterial O2 content - Venous O2 content).
What are the two equations for Mean arterial pressure (P) AKA (MAP)?
P = Cardiac output (Q) x Peripheral resistance (R). MAP = (2/3) diastolic pressure + (1/3) systolic pressure. Or (2x diastolic + 1 systolic and divide it by 3).
What is the pulse pressure?
Systolic pressure - Diastolic pressure.
How does exercise affect CO?
Initially: ^ CO due to ^ SV. Sustained exercise: CO maintained due to ^ HR. However, CO goes down if HR is too high (the diastolic pressure becomes incomplete, so you can’t fill up your ventricles). That’s why A-fib and V-tach = \/ CO.
What is preload?
Pressure at EDV. It is end-diastolic pressure which is roughly equal to atrial pressure, which is roughly equal to central venous pressure.
What is afterload?
The mean arterial pressure (MAP), which is roughly equal to Total peripheral resistance (TPR).
What are things that increase preload?
Exercise. ^ blood volume (over-transfusion, over-hydration, pregnancy).
What are drugs that \/ preload?
Venodilators: Nitrates (nitroglycerin).
What are drugs that \/ afterload?
Vasodilators like hydralazine.
What affects stroke volume (SV)?
Contractility. ^ afterload (\/ SV). ^ preload (^ SV).
How do we increase contractility?
Catecholamines (Beta1 receptors on the heart: ^ activity in the Ca2+ pump in the sarcoplasmic reticulum).
How do we decrease contractility?
Beta1-blockers. HF. Acidosis. Hypoxia. Hypercapnia. Non-dihydropyrine CCBs.
