Lecture 10- Cardiac Phys II (Cardiac output) Flashcards
What is a cardiac cycle?
“A single cardiac cycle includes all of the events associated with one heartbeat.
Thus, a cardiac cycle consists of systole and diastole of the atria plus systole
and diastole of the ventricles”
Cardiac cycle refers to all events associated with blood flow
through the heart
What is the difference between systole and diastole?
– Systole (pronounced “sis-ter-lee”) – contraction of heart muscle
– Diastole (pronounced “dias-ter-lee”) – relaxation of heart
muscle
Go through the phases of the cardiac action potential and what does it tell you?
- rapid depolarization due to Na+ inflow when voltage-gated fast Na+ channels open
- plateau of membrane potential (a maintained depolarization) due to Ca2+ ions flowing in when voltage-gated slow Ca2+ channels open and K+ outflow when some K+ channels open
- repolarization due to the closure of Ca2+ channels and K+ outflow when additional-gated K+ channels open
The atrial systole has which 3 parts of the cardiac cycle?
- arteriol systole
- ventricular systole
- relaxation
Go through the process of the cardiac cycle and all its phases
- Depolarization of SA node
- atrial depolarization (pwave) - Ventricular filling – mid-tolate diastole
– Heart blood pressure is
low as blood enters atria
(passively) and flows into
ventricles
– AV valves are open, then
atrial systole occurs - At the end of atrial
systole, the ventricle contains
~130mL blood - QRS complex marks onset
of ventricular depolarization - Ventricular depolarization,
ventricle systole. Pressure ↑ in
ventricles putting pressure on AV
valves causing isovolumetric
contraction (ie all 4 valves closed,
ventricular volume same) - Ventricular contraction,
pressure
↑. When L ventricular pressure >
aortic pressure (~80mmHg) AND R
ventricular pressure > pulmonary
trunk pressure (20mmHg), aortic
valves open ventricular ejection - L ventricle ejects blood into aorta +
R ventricle ejects into pulmonary
trunk - T wave == onset of ventricular
repolarization - Ventricular repolarization
ventricular diastole. Ventricular
pressure ↓, blood in aorta and
pulmonary trunk flows back,
pressure equalizes, and all 4
valves close (isovolumetric
relaxation) - Ventricles relax, pressure ↓.
AV valves open, ventricles fill. P
waves appear, starting the next
cycle
What is the ventricle systole? What are the phases that make up the ventricle systole?
- Ventricular depolarization
ventricle systole. Pressure ↑ in
ventricles putting pressure on AV
valves causing isovolumetric
contraction (ie all 4 valves closed,
ventricular volume same) - Ventricular contraction pressure
↑. When L ventricular pressure >
aortic pressure (~80mmHg) AND R
ventricular pressure > pulmonary
trunk pressure (20mmHg), aortic
valves open ventricular ejection - L ventricle ejects blood into aorta +
R ventricle ejects into pulmonary
trunk - T wave == onset of ventricular
repolarization
What are the phases of the relaxation phase?
- Ventricular repolarization
ventricular diastole. Ventricular
pressure ↓, blood in aorta and
pulmonary trunk flows back,
pressure equalizes, and all 4
valves close (isovolumetric
relaxation) - Ventricles relax, pressure ↓.
AV valves open, ventricles fill. P
waves appear, starting the next
cycle
What is auscultation?
Auscultation (listening to the heart)
How are valves affected when blood is leaving and returning from the heart?
- when blood is returning to the heart and fills the atria it puts pressure against the arterioventricular valves
- as the ventricles fill, arterioventricular valve flaps hang limply into the ventricles
- when atria contracts blood is forced into the ventricles
- when ventricles contract, blood is forced against the arterioventricular valve cusps
- the arterioventricular valves close
- papillary muscles contract and chorsae tendineae tighten, this prevents valve flaps from everting into the atria
as ventricles contract and intraventricular pressure rises blood is pushed up against the semilunar valves and forces them to open
as ventricles relax and intraventricular pressure falls, blood flows back from arteries and fills the cusps of the semilunar valves and forces them to close
What are the first and second sounds associated with auscultation?
First sound (Lub) occurs
as AV valves close and
signifies beginning of
systole (contraction)
– Second sound (Dub)
occurs when SL valves
close at the beginning of
ventricular diastole
(relaxation)
Define cardiac output
Cardiac Output is the amount of blood pumped by each ventricle in one
minute
How is CO calculated?
CO is the product of stroke volume (SV) and heart rate (HR)
* HR is the number of heart beats per minute
* SV is the amount of blood pumped out by a ventricle with each beat
Cardiac reserve is the difference between resting and maximal CO
CO=SV x HR
What is SV? How is it calculated? What is SV affected by?
SV = end diastolic volume (EDV) minus end systolic volume (ESV)
– EDV = amount of blood collected in a ventricle during diastole
– ESV = amount of blood remaining in a ventricle after contraction
At rest, SV is 50–60% of the EDV because 40–50% of the blood remains in
the ventricles after each contraction (ESV)
SV is affected by three factors:
1. Preload – degree to which ventricles are stretched by the blood
2. Contractility – cardiac cell contractile force
3. Afterload – back pressure exerted by blood in the large arteries leaving the
heart
What are intrinsic and extrinsic mechanisms of cardiac output?
What does the Frank-Starling law tell us about the heart?
Preload (degree of stretch) of cardiac muscle cells before they contract is the
critical factor controlling SV
The volume of blood ejected by the ventricle depends on the volume
of blood present in the ventricle at the end of diastole
Slow heartbeat and exercise (more next time) increase venous return to the
heart (filling time is longer), increasing SV
Blood loss and extremely rapid heartbeat (eg >160bpm) decrease SV (short
filling time
