5 - SAM

What are the two sets of heart valves?

Atrioventricular (AV) valves and semilunar valves

What is the function of the heart valves?

Direct blood flow in one direction and prevent backflow

Which AV valve is on the right side of the heart?

Tricuspid valve

Which AV valve is on the left side of the heart?

Mitral (bicuspid) valve

Which semilunar valve is on the right side of the heart?

Pulmonary valve

Which semilunar valve is on the left side of the heart?

Aortic valve

What happens during atrial systole?

The atria contract and the AV valves are open so blood enters the ventricles

What happens during ventricular systole?

The ventricles contract, the AV valves close, and the semilunar valves open so blood leaves the heart

What is diastole?

Relaxation of both the atria and ventricles

What ensures one-way blood flow through the heart?

Pressure differences between chambers and normal functioning valves

What creates the normal heartbeat sounds?

Sequential closing of the two sets of heart valves

What is cardiac output (CO)?

The volume of blood pumped over a unit of time, measured in L/min

What is the equation for cardiac output?

CO = HR × SV

What is stroke volume (SV)?

The amount of blood ejected by the left ventricle with each heartbeat

What is the equation for stroke volume?

SV = EDV − ESV

What are the three determinants of stroke volume?

Preload, contractility, and afterload

What is preload?

The stretch of heart muscle fibers at the end of diastole, reflecting ventricular filling and venous return

What happens to stroke volume when preload increases within physiologic limits?

Stroke volume increases

What is contractility?

The intrinsic ability of the heart muscle to contract independent of preload

What happens to stroke volume when contractility increases?

Stroke volume increases

What is afterload?

The resistance the left ventricle must overcome to eject blood during systole

What happens to stroke volume when afterload increases?

Stroke volume decreases

What are major examples of increased afterload?

High blood pressure and aortic stenosis

What is the Frank-Starling law?

Within physiologic limits, greater ventricular filling/stretch produces a stronger contraction and greater stroke volume

What is mean arterial pressure (MAP) related to?

Cardiac output and systemic vascular resistance

What is the equation for MAP?

MAP = CO × SVR

What happens to MAP when cardiac output increases?

MAP increases

What happens to MAP when systemic vascular resistance increases?

MAP increases

What happens to MAP when systemic vascular resistance decreases?

MAP decreases

Why can septic shock cause low blood pressure despite high cardiac output?

Vasodilation decreases systemic vascular resistance, causing MAP to decrease

What is vascular compliance?

The volume of blood a vessel can hold at a given pressure

Where does most of the blood volume in the circulation reside?

The systemic veins

What vessels account for most systemic vascular resistance?

The microcirculation, especially the arterioles

Where is blood flow velocity highest and lowest?

Highest near the heart in the aorta/pulmonary artery and lowest in the capillaries

What are the major goals of circulation?

Perfusion/oxygen delivery, waste removal, and maintenance of blood pressure and blood volume

What is the general compensatory response to cardiac disease/injury?

Decreased cardiac output triggers compensatory mechanisms that increase preload/afterload and cardiac pressure/volume

Which major neurohumoral systems are activated during cardiac compensation?

SNS, RAAS, ADH, and endothelin

Why can cardiovascular compensation become harmful?

Chronic compensation can create a vicious cycle of increased pressure/volume, congestion, remodeling, and worsening cardiac function

Where is angiotensinogen produced and where is renin released?

Angiotensinogen is produced by the liver and renin is released by the kidney

What does renin do?

Converts angiotensinogen to angiotensin I

What converts angiotensin I to angiotensin II?

Angiotensin-converting enzyme (ACE)

What are the major effects of angiotensin II?

Vasoconstriction, increased aldosterone release, increased thirst, increased ADH release, and sympathetic stimulation

What are the important chronic effects of angiotensin II?

Myocardial fibrosis and cardiac remodeling

What are natriuretic peptides and what is their general effect?

ANP, BNP, and CNP

Where are ANP and BNP primarily produced?

ANP is produced in the atria

What stimulates ANP/BNP release?

Wall stress/distension

What are the major effects of ANP and BNP?

Vasodilation, natriuresis, and blunting of RAAS

What does the Wiggers diagram show?

The electrical, mechanical, pressure, volume, valve, and heart sound events of the cardiac cycle over time

What produces S1?

Closure of the mitral and tricuspid valves

What produces S2?

Closure of the aortic and pulmonary valves

What is S3?

A diastolic sound associated with ventricular filling

What is S4?

A diastolic sound caused by atrial contraction against a stiff/non-compliant ventricle

What is an important clinical association for S4?

Hypertrophic cardiomyopathy in cats

What is an important clinical association for S3?

Dilated cardiomyopathy in dogs

What is a systolic murmur?

A murmur occurring between S1 and S2

What is a diastolic murmur?

A murmur occurring between S2 and the next S1

What is a continuous murmur?

A murmur present throughout both systole and diastole without a break

What is the point of maximal intensity (PMI)?

The location where a murmur is loudest

What is the difference between an apical and basilar murmur location?

Apical murmurs are associated with the AV valve regions

How are heart murmurs graded?

From I/VI to VI/VI, with VI/VI being the loudest

What is a classic cause of a continuous murmur in a young dog?

Patent ductus arteriosus (PDA)

What are the three main things used to characterize a heart murmur?

Location, timing, and loudness