Definitions and Cardiac Output Basics Flashcards
What is “pressure”?
Force per unit area exerted by gas or fluid on its container - generally expressed as a pressure difference (difference between pressure inside vs. outside), etc.
What is flow rate?
“L/min”, ie Volume transferred from one location to another per unit time.
What is flow velocity?
Cm/sec. Speed with which volume is moving.
What is flow resistance?
Resistance to flow provided by a structure. For blood flow it is related to radius of vessels and viscosity of blood.
What are the units of flow resistance?
Wood units. (dynes/sec/cm^5). BP/flow rate. Whatever.
What is compliance?
The relationship between a substance distending a structure and its volume; Change in Volume/Change in Pressure. It is a physical property of the walls of the structure.
What is the rule of thumb for compliance? What changes this rule of thumb a bit?
Low compliance with stiff walls, higher compliance with stretchy walls. This changes with the LaPlace relationship, that basically states that with increase in size, greater pressure is required to maintain a certain tension.
What is cardiac output?
SV * HR
During early stages of exercise, what maintains CO?
Increased HR and Increased SV
During the late stages of exercise, what maintains CO?
Incr HR only. SV plateaus.
What happens to CO when HR is increased too much?
CO can drop because diastole is preferentially shortened with Incr HR, so there is less filling time, and thus less output.
What is the Fick principle? What’s an easier way of arranging it so it makes sense?
CO = (rate of oxygen consumption)/(arteriovenous oxygen difference).
Makes more sense like:
Rate of oxygen consumption = CO * AV Diff.
How does mean arterial pressure relate to CO?
MAP = CO * Total Peripheral Resistance
How can you calculate MAP?
MAP = 2/3 Diastolic + 1/3 Systolic
What is pulse pressure?
Pulse pressure = systolic pressure - diastolic pressure.
What causes a widened pulse pressure?
Increase in SV, or decrease in arterial compliance.
How does cardiogenic shock, heart failure, cardiac tamponade, and aortic stenosis change pulse pressure?
Decreases. All lower SV.
How do aortic regurgitation, aortic stiffening, exercise, and hyperthyroidism change pulse pressure?
Increase pulse pressure.
How does obstructive sleep apnea change pulse pressure and why?
Incr pulse pressure due to increased sympathetic tone.
What factors increase stroke volume?
Incr contractility, increased preload, decreased afterload
Why do catecholamines increase contractility?
Increased activity of Ca2+ pump in sarcoplasmic reticulum
What is the effect of increased intracellular calcium on contractility?
Increases contractility
Why does decreased extracellular Na+ increase contractility?
Decreases the activity of the Ca2+/Na+ exchanger, which normally removes Ca2+ from cell by taking in extracellular Na+
How does Digitalis increase contractility?
Blocks Na+/K+ pump. Increased intracellular Na+ . Less gradient for Na+ to come in, decreased removal of Ca2+ from cell by Na+/Ca2+ antiporter.
Why do beta blockers decrease contractility?
Decreases intracellular cAMP
What is the effect of acidosis on cardiac contractility?
Decrease
What is the effect of hypoxia/hypercapnia on Contractility?
Decrease
What is the effect of Non Dihydropyridine Ca2+ blockers on cardiac contractility?
Decrease
What factors increase myocardial demand?
Contractility, Afterload, Heart Rate, Diameter of Ventricle
What is the definition of “preload”?
Ventricular end-diastolic volume
What are the determinants of preload? What decreases preload?
Venous tone and circulating blood volume. Venodilaters decrease preload.
What is the definition of afterload?
Approximated by mean arterial pressure. Increased afterload –> increased pressure –> increased wall pressure.
LV compensates for afterload by thickening in order to decrease wall tension.
What is the effect of vasodilators on afterload?
Decrease afterload.
What is the effect of ACEis and ARBs on cardiac output variables?
Decrease both preload and afterload.
