Cardiac Output Flashcards
What is the definition of Cardiac Output?
What is the formula?
The quantity of blood pumped out of the heart each minute. (Refers to blood to tissue)
CO = HR x SV
Explain what drives Cardiac output.
If tissue demand increases, cardiac output increase.
Tissue energy demand drives cardiac output up to the heart’s maximum capacity. At max capacity, the heart takes over cardiac output.
When the body is at rest, what is Cardiac Output, Heart Rate, and Stroke Volume?
CO – 4 - 7 L/min (body size)
Heart Rate 60-80 beats/min (fitness level)
Stroke Volume 65-75 mL/beat (body size)
When the body is performing at its maximum, what is Cardiac output, Heart rate, and Stroke volume?
CO 12-35 L/min (body size)
Heart Rate 150-200 beats/min 220-age=max…regression.
Stroke Volume 100-220 mL/beat (fitness)
What two factors of the heart can be adjusted to alter cardiac output?
Define Chronotropic Effects
Define Inotropic Effects
And what autonomic nervous system regulates each.
CO can be altered by either altering HR or SV
Chrono…change in CO is accomplished by ALTERING HEART RATE (Sympathetic and Parasympathetic)
Ino…change in CO is accomplished by altering SV. (Sympathetic)
What 2 factors effect Chronotropic regulation?
Autonomic Nervous System—norepinephrine (sympathetic)
Adrenal Medullary Hormones–epinephrine, and nor-epinephrine.
How does sympathetic work to increase heart rate?
Increase rate.
The sympathetic nervous system enhances the rate of spontaneous depolarization through a cAMP-dependent mechanism that enhances movement of sodium and calcium into the pacemaker cell. More open Na+ and Ca++ channels increase the rate of polarization. This causes pacemaker potential threshold to be shorter.
How does parasympathetic work to decrease heart rate?
The parasympatheic nervous system decreases the rate of spontaneous depolarization through muscarinic receptors by decreasing the movement of calcium and sodium into the cell and increasing the movement of potassium out of the cell.
Inotropic Regulation
What are the 3 mechnisms?
Preload (EDV) on heart.
Myocardial contractility
Afterload (Total peripheral Resistance TPR)
Frank-Starling Law of the Heart (effect of preload)
What is it? What is it directly related to?
Force of myocardial contraction is related to muscle fiber length prior to contraction…Muscle fiber length is directly related to EDV.
or
The more you stretch muscle prior to contraction, the more force you get out of the contraction–snapping rubber bands. Applies to heart muscle. Returning blood during diastole stretches the heart. (EDV)
Myocardial Contractility
What is contractility?
What ion influences it?
How do nerves and hormones effect it?
Contractility refers to the contractile force of a muscle at a fixed length.
Myocardial contractility is influenced by the amount of Ca++ present in the cytoplasm when contraction begins at any given length. Sympathetic activity.
Sympathetic nerve activity and adrenal medullary activity increase myocardial contractility.
If Myocardial contractility is the measure of relative Force of contraction of the heart, what is its equation?
How are absolute force and relative force related in this instance.
Continuity=F/L = SV/EDV —– Ejection Fraction.
A change in ventricular contractility means a change in the force of ventricular contraction at any given EDV. Any factor that causes the ventricles to contract with more force will tend to make stroke volumes larger, which will in turn increase cardiac output.
(one can have greater contractility at the same EDV)
Total Peripheral Resistance (afterload)
What is it?
What determines it?
how is it related to SV?
RESISTANCE of the VASCULATURE to blood flow from the heart.
Determined primarily by the level of constriction or dilation of the arterioles.
Stroke volume is inversely related to afterload.
(Greater resistance, lower SV)
What is the driving force of blood flow and blood pressure?
Pressure Gradient.
Systemic and Pulmonary Circuit Pressure Gradients/
What are Systemic Circulation and Pulmonary Circulation? 2 things each.
Systemic Aortic pressure (mean arterial pressure or MAP) as it leave the heart. MAP= (SP + 2DP)/3 Large veins (central venous pressure or CVP)
Pulmonary Circulation
Pumonary arterial pressure
Pulmonary venous pressure.
