Heart Pump Flashcards
What is the equation for Cardiac Output?
CO = SV x HR
Proper filling of ventricles depends on three things:
- Filling pressure of blood returning to heart and atria
- Ability of AV valves to open fully (not stenotic)
- Ability of ventricular wall to expand passively with little resistance (high compliance) - healthy heart is very compliant - filling occurs with only small increases in ventricular pressure
What is diastolic pressure?
- The lowest pressure seen in the aorta
- Happens at the end of diastole (after filling)
Hematocrit
Fraction of blood volume occupied by cells
What is the initial stage of ventricular contraction called where the volume of the ventricle does not change?
Isovolumetric contractile phase of systole (both valves are closed)
Why does increasing circulating catecholamines cause an increase in stroke volume?
It increases contractility via SNS
Why does a decrease in arterial pressure cause an increase in stroke volume?
It decreases afterload
Why does an increase in filling pressure increase SV?
It increases preload
Isovolumetric Contraction
All valves are closed, no change in volume but heart is contracting
Isovolumetric Relaxation
All valves are closed but heart is relaxing
Arterial Pulse Pressure =
PP = Systolic - Diastolic
What is different between the right and left heart during the cardiac cycle?
Magnitude of peak systolic pressure is lower in RIGHT because less resistance to flow from lungs vs. systemic organs
Ps = 24 mmHg
Pd = 8 mmHg
What causes the Jugular Venous pulse?
- Pressure pulsations occurring in the right atrium
- Transmitted to large veins near the heart
- a wave: atrial contraction
- c wave: bulging of tricuspid valve into right atrium due to ventricular contraction
- v wave: RA and central veins re-filling behind closed tricuspid valve (blood returning from peripheral organs)
What is S1?
Closure of the AV valves
What is S2?
Closure of aortic and pulmonic valves
What happens during the physiological splitting of S2?
Pulmonic valve closes slightly after aortic valve
- Inspiration causes increase in this gap to 30-60 ms
- Inspriation-induced changes in intrathoracic pressure and pulmonary vascular resistance lead to prolonged right ventricular ejection
What is S3?
Not normally heard. Presence may indicate left ventricular failure (but can also sometimes be detected in normal children!)
What is S4?
Presence may indicate ventricular diastolic stiffness
Ejection Fraction (EF) =
SV/EDV
or
SV/Peak Volume
Preload:
End-diastolic pressure/vol. that stretches the ventricle to its greatest dimension under physiologic demand
- -The passive/resting tension placed on cardiac muscle cells before contraction
- -EDV or arterial pressure are used as surrogates
What is Starling’s Law of the Heart?
Stroke Volume increases as cardiac filling increases
What will an increased preload do?
- Increase initial muscle fiber length, thus increase the extent of shortening during contraction
- Increase end-diastolic volume and stroke volume
What is afterload?
Tension or stress that develops in cardiomyocytes of the left ventricle during ejection/contraction
- The active tension placed on cardiac muscle cells during contraction (A fan of R the left ventricle must overcome to circulate blood)
- As afterload increases, CO decreases
What is used as a surrogate for mean ventricular after load?
Mean Arterial Pressure
MAP = DP + 1/3 PP
What does increased after load do?
Decreases SV
Ex: hypertension, aortic valve obstruction
Increased contractility will ___ ESV.
Decrease, Thus it increases SV.
What is Ejection fraction used for?
Clinically useful variable to assess cardiac muscle contractility (EF = SV/EDV)
What 5 effects are initiated by NE interacting with Beta-1 Adrenergic receptors (sympathetic nervous system)?
- Inc. HR
- Inc. rate of AP conduction
- Inc. in cardiac contractility
- Inc. in rate of cardiac relaxation.
- Dec. in cardiac action potential duration.
What is the positive chronotropic effect?
Inc. in HR caused by NE.
Activates funny-current in SA node
What is the positive dromotropic effect?
Inc. in rate of AP conduction
-Alters conductivity of gap junctions
What is the positive iontropic effect?
Increases in cardiac contractility
- Inc. contractile ability of cardiac muscle at any given preload
- Activates the Ca2+ current and increases Ca2+ release from SR
What is the lusitropic effect?
Inc. in rate of cardiac relaxation.
- This minimizes the detrimental effects of high heart rates on diastolic filling time
- Inc. Ca2+ uptake by SR
What contributes to the lusitropic effect?
Dec. in cardiac AP duration, which promotes early relaxation and contributes to the positive lusitropic effect
-Early activation of delayed K+ current
What is the primary source of energy for the heart?
60-90% of fuel is ATP from oxidative phosphorylation
What is the primary source of cardiac energy for adults? Fetal and newborn? Severe heart failure?
Adult –> Fatty acids
Fetal & Newborn –> Glucose and Lactate
Severe heart failure –> Observable shift back to glucose metabolism
What does the heart have a lot of?
- Mitochondria
- Oxygen-binding protein myoglobin
What does the heart rely on for ATP?
Aerobic pathways
What percentage of myocardial O2 consumption/energy use is devoted to what things?
25% - basal metabolism
75% - muscle contraction
–Isovolumetric - 50%
–Isotonic contraction - 25%
How to reduce O2 consumption?
Reduce cardiac preload -T = P x r (laplace) At larger radius, more tension needed, thus more work and energy Reduce cardiac afterload Reduce cardiac contractility Reduce heart rate
What is the most important determinant of oxygen consumption?
Heart Rate
- More O2 needed to contract fast
- More efficient to achieve CO with low HR and high SV than vice versa
