Cardiovascular Physiology Rapid Review Flashcards
Systole
Heart contracts and blood is ejected
Blood pressure is greatest during systole.
In Ventricular systole, ventricles pump blood to the blood vessels. Atrial systole, atria pump blood into relaxed ventricles
Diastole
Heart relaxes and fills with blood. Blood pressure is lowest during diastole
Pulse Pressure
Difference between the systolic and diastolic pressures
Valves of the heart
Mitral valve - AV valve that prevents backflow from the left ventricle into the left atrium
Tricuspid valve - AV valve that prevents backflow from the right ventricle into the right atrium
Semilunar valves: aortic and pulmonic, prevent blood from flowing back into ventricles during ventricular diastole. Aortic separates left ventricle from aorta. Both valves have three cusps.
Heart sounds
S1 - closure of AV valves
S2 - closure of semilunar valves
S3 - ventricular gallop (early to middle diastole, during rapid ventricular filling)
S4 - Atrial gallop (late diastole, atrial contraction against a stiffened ventricle)
S3 sound
Ventricular gallop, may be caused by a sudden limitation of ventricular expansion. Normal in children and young adults, but may be caused by rapid ventricular expansion associated with regurgitation of blood across an incompetent valve, which increases the rate of ventricular filling during diastole (in adults; aortic regurgitation)
S4 sound
Heard in late diastole, caused by atrial contraction against a stiffened ventricle. Indicates cardiac disease. Indicated decreased ventricular compliance (the ventricle does not relax as easily) which is commonly associated with ventricular hypertrophy or scarring. An S4 is almost always present after an acute MI.
Describe ventricular pressure changes
Ventricular pressure gradually increases in volume during diastole, which causes the ventricular pressure to increase
Atrial contraction causes a slight “hump” before systole in the final phase of ventricular filling.
The AV valves close when systole begins and the ventricular pressure is greater than the atrial pressure.
Isovolumetric contraction - Pressure continually builds until the ventricular pressure exceeds that of the aorta or the pulmonary artery.
The semilunar valves open.
Blood is ejected into the circulation.
Semilunar valves close when the pressure inside the ventricles is less than that of the aorta and pulmonary artery.
Isovolumetric Relaxation - Pressure decreases (same volume of blood, muscle relaxes)
When interventricular pressure is less than atrial pressures, AV valves open again, and ventricular filling of diastole begins.
Cardiac Output
Volume of blood pumped out of the heart each minute.
Product of heart rate and stroke volume.
Used to assess cardiac performance
5 L/minute in healthy adult (70 Bpm * 70 mL/beat)
Can also be measured using whole body oxygen consumption
Fick Principle
Oxygen consumption by the body is a functino of the amount of blood delivered to the tissues (cardiac output, CO) and the amount of oxygen extracted by the tissues (arteriovenous oxygen difference):
CO = oxygen consumption / (oxygen concentration in arteries - oxygen concentration in veins)
Stroke Volume
Volume of blood ejected from the ventricle during ventricular systole
Determines Pulse Pressure
SV = EDV (End diastolic volume) - ESV (End systolic volume)
Ejection Fraction
Percentage of blood in the ventricle at the end of diastole that is pumped into the circulation with each heartbeat.
SV (stroke volume) / EDV (End diastolic volume)
Determinants of Stroke Volume
Preload, Contractility, and Afterload
Preload
Degree of tension (load) on the ventricular muscle when it begins to contract (Volume of blood within the ventricle at the end of diastole) (venous return)
Frank-Starling relationship
Length-tension relationship of the heart theory
Increased ventricular wall tension associated with increased EDV stretches ventricular myocytes and results in a greater overlap of actin and myosin filaments, which causes more forceful contractions
Second theory of why an increased EDV increases SV
The contractile apparatus of cardiac myocytes becomes more sensitive to cytoplasmic calcium as the myocytes are stretched under conditions associated with increased preload
Contractility
Measure of the forcefulness of contractions at any given preload (independent of myocardial wall tension at EDV)
Inotropic state of the heart
(Drugs, sympathetic excitation, and heart disease may affect contractility)
What affects contractility?
Drugs, sympathetic excitation, and heart disease
Afterload
The pressure or resistance against which the ventricles must pump blood (including systemic blood pressure) and any obstruction to outflow from the ventricle (such as stenotic aortic valve
If Afterload increases, SV ____.
decreases
Laplace equation
Rho = P x r / 2h, where rho = wall tension, P = intraluminal pressure, r = intraluminal radius, and h = wall thickness
Stroke work
Measure of the mechanical work performed by the ventricle with each contraction
Composed of Pressure-volume work and Kinetic energy work
Pressure-volume work
work used to push the SV into the high-pressure arterial system and is equal to the systemic arterial pressure multiplied by the SV
Kinetic energy work
Supplied by ventricular contraction that is used to move the ejected blood at a certain velocity