The Cardiac Cycle

what does the cardiac cycle refer to?

the events that relate to the flow of blood through the heart during one complete heartbeat

what does the cardiac cycle include?

- pumping phases (pump cycle)

- valve opening and closing

- pressure changes in the atria, ventricles, and aorta

- volume changes in the ventricles

- heart sounds associated with valve opening and closing

what characterizes phase 1 of the cardiac cycle?

(end of 4)

early diastole - mid/late diastole

- relax to get filled with blood (ventricular filling)

- contraction begins in the atrium (atrial contraction)

what characterizes phase 2 of the cardiac cycle?

beginning of systole

- ventricles filling, creating pressure

what characterizes phase 3 of the cardiac cycle?

systole

- ventricular ejection (blood ejected into pulmonary and aorta arteries)

what characterizes phase 4 of the cardiac cycle?

isovolumetric relaxation - building up of pressure in the valves, no more blood is entering the ventricles (preparing to return to phase 1)

what characterizes systole?

contraction

what characterizes diastole?

relaxation

when are atrioventricular valves open?

during phase 1

when are aortic and pulmonary valves open?

phase 3

when are atrioventricular valves closed?

phase 3

when are aortic and pulmonary valves closed?

phase 1

what are the inbetween phases for opening on valves?

phases 2 and 4

what is the ventricular pressure needed for systolic contractions to occur?

120 mmHG

what happens to atrial pressure when ventricular pressure is high?

it is low

what is the value of aortic pressure during ventricular ejection?

120 mmHG

what is the dicrotic notch?

the aortic tissue recoiling after its expansion (following ventricular ejection)

- also known as "rebound"

- blood is spit into the arteries so it can be delivered to the body

- diastolic pressure is @ about 80 mmHG

what MAP?

mean arterial pressure during one cardiac cycle

- typically 70 - 100

are ventricles every fully emptied?

no

how is end-systolic volume (ESV) affected by ventricular contraction?

more contraction = less volume

how is end-diastolic volume (EDV) affected by ventricular contraction?

more relaxation = more volume (blood is not being pumped out)

how do you calculate stroke volume?

SV = EDV - ESV

ex.

130 mL - 60 mL

what is the physiology behind heart sounds?

the in between phases (2 and 4) - because the blood is moving through the valves

hwo do you calculate cardiac output?

CO = HR x SV

ex.

72 bpm x 0.07 L/beat = 5L/min

how do you calculate ejection fraction (EF)?

EF = SV/EDV

ex.

70 mL/135mL = 0.52

which is 52% = contractility efficiency

what is stroke volume?

how much blood was ejected

what is end diastolic volume?

how much blood COULD be ejected

when is ejection efficiency important to know?

when people have myocardial infarctions = heart attack (HA)

how can you test ejection efficiency?

echo cardiogram

what is the venous return?

flow of blood back to the right atrium

what is preload?

the amount of stretch of the ventricular wall myocardium; related to end-diastolic volume (EDV)

what is afterload?

the combined load of EDV and arterial resistance during ventricular contraction; increased afterload = decreased SV

what system innervates most of the areas of the heart?

autonomic nervous system (sympathetic and parasympathetic)

where do sympathetic fibers project to?

the SA node, AV node, and ventricular myocardium (makes sense b/c these stimulate contraction which increases during fight/flight)

- HR increases

increase forcefulness of contraction (contractility)

where do parasympathetic fibers project to?

the SA node and AV node resulting in decreased HR (resting)

epinephrine released from the adrenal medulla following sympathetic stimulation does what to HR?

increases it

- increases contractility

what will increased HR increase?

CO - cardiac output

why?

b/c CO = HR x SV

what does contractility do to ESV?

decreases, resulting in greater SV

how can SV be intrinsically regulated?

by venous return; venous return affects EDV and EDV affects SV

what is Starling's Law?

greater venous return = greater CO due to greater SV

what part of the parasympathetic nervous system inputs to the SA node?

medulla via the vagus nerve

what part of the sympathetic nervous system inputs to the AV node, SA node, adn ventricular myocardium?

cervical and thoracic (T1-T4)

why can the heart still contract as more pressure is created and actin and myosin filaments are farther apart?

the heart is elastic - it can bounce back together to eject blood (contraction)

an increase in EDV causes...

an increase in stroke volume (SV)

where is stroke volume centralized?

ventricular myocardium

where is the HR located?

the SA node

what is the driving force for venous return?

the pressure gradient between the peripheral veins and the right atrium

what affects venous return?

venous pressure

what can venous pressure/venous return be influenced by?

- skeletal muscle pump

- respiratory pump

- blood volume

- posture

- blood pooling or in muscles/skin post-exercise

PV=nRT

what do increased blood flow requirements by muscles result in?

increased cardiac output

what is increased cardiac output accomplished by?

increased heart rate and stroke volume

what causes increases in stroke volume?

increased EDV as CVP (central venous pressure) increased due to venoconstriction and muscle/respiratory pump actions

ex. working out

what causes a slight increase in MAP?

increased CO

when MAP increases as a result of increased CO, what decreases?

why?

- TPR (total peripheral resistance) by systemic blood vessels

- due to vasodilation in working muscles