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events occurring during the cardiac cycle
isovolumetric ventricular relaxation
atrial and ventricular diastole
atrial systole
isovolumetric ventricular contraction
ventricular systole
phases of blood pressure changes
systole (contraction/ejection)
diastole (relaxation/filling)
isovolumetric phases
change in blood pressure during systole
left ventricle contracts, causing pressure to rise rapidly until it exceeds aortic pressure, opening the aortic valve
during rapid ejection, aortic pressure reaches its peak (systolic pressure)
changes in blood pressure during diastole
following ventricular contraction, the aortic valve closes to prevent backflow
aortic pressure gradually decreases (diastolic pressure) as blood moves into peripheral vessels
changes in blood pressure during isovolumetric phases
before ejection, pressure builds rapidly within the ventricle while all valves are closed
during relaxation, pressure drops significantly before the mitral valve opens for refilling
left ventricle pressure during cardiac cycle
ventricular pressure is initially lower than aortic pressure
when ventricular pressure is greater than aortic pressure, aortic valve opens
aortic pressure then tracks ventricular pressure
when pressure in the ventricles drops below aortic pressure, aortic valve closes
aortic notch
dip in aortic pressure when the aortic valve closes
Windkessel effect
aortic and systemic pressure is kept above 0 due to the elasticity and compliance of arterial and aortic walls, resulting in continuous blood flow (rather than pulsatile)
importance of Windkessel effect
evens out pressure in the system
allows blood to continue flowing during diastole
blood flow via coronary circulation
isovolumetric ventricular contraction
heart contracts, resulting in closure of atrioventricular valves
pressure increases due to contraction, but both valves are closed so volume doesn’t change
ventricular systole
pressure increases until the pressure in the ventricles is greater than the pressure in the aorta and pulmonary trunk
pulmonary and aortic semilunar valves open
blood flows out of the ventricles
ventricle pressure peaks and starts to fall
isovolumetric ventricular relaxation
ventricular contraction stops, pressure drops
aortic and pulmonary semilunar valves close
pressure in aorta and pulmonary trunk remain high due to Windkessel effect
as soon as valves close, enter a phase of ventricular relaxation with no change in ventricular volume
pressure drops to almost 0
ventricular filling
pressure lower in ventricles than atria, AV valves open
sinus node fires, atria contract and push a little more blood into the ventricles (atrial kick)
aortic pressure
spikes due to ventricular contraction
falls slowly due to Windkessel effect
ventricles fill from the beginning of diastole
pressure in left ventricle is slightly lower than left atria, mitral valve is open
small difference in pressure is enough to mostly fill the ventricle passively
P wave
atrial depolarization and contraction
atrial kick
most filling occurs when there is no contraction of either the atria or ventricles
QRS
ventricle depolarization and contraction
pressure increases
pressure in the ventricle is higher than atria about 10 ms after contraction starts → mitral valve closes
pressure continues to increase
first heart sound
closing of the mitral valve
second heart sound
closing of the aortic semilunar valve
aneroid sphyngmomanometer
consists of a cuff with a bladder, an inflating bulb, a needle valve, and an aneroid gauge (measures pressure in the cuff)
mercury sphygmomanometer
consists of a cuff with a bladder, an inflating bulb, a needle valve, and a column of mercury (to measure pressure)
methods of indirect measurement of blood pressure
palpation
auscultation
oscillometric
palpation
fill cuff until no pulse is detected
release pressure (needle valve) slowly
point at which pulse is felt = systolic blood pressure
brief period when pulse pressure > cuff pressure and blood gets through, pressure is close to maximum
auscultation
fill cuff past systolic pressure
release pressure (needle valve) slowly
listen for turbulent flow, start of Korotkoff sounds = systolic pressure
no sound is heard when there is no flow or laminar flow
flow expansion results in turbulence, which can be heard
continue releasing pressure while listening
end of Korotkoff sounds = diastolic pressure
oscillometric
fill cuff to block blood flow
slowly release cuff pressure (allows small pressure oscillations in the artery from blood pulses)
pressure transducer measures oscillations
calculation of the point of maximum oscillation
corresponds to the mean arterial pressure (MAP)
MAP is then used to estimate systolic and diastolic pressures