Cardiovascular physiology Flashcards
What causes the first heart sound?
The closure of the atrioventricular valves - mitral and tricuspid.
This indicates the beginning of systole and the start of isovolumetric contraction.
What percentage of ventricular filling does atrial contraction contribute to?
25–30%.
What are normal values for end diastolic volume (EDV) and end systolic volume
(ESV)?
EDV- volume in the ventricle at the end of diastole = 130 mL.
ESV- volume remaining in the ventricle at the end of systole = 60 mL.
How is the stroke volume (SV) calculated?
SV is the amount of blood pumped out of the ventricle in one contraction. This is calculated by; SV = EDV – ESV. SV = 130 mL – 60 mL. The stroke volume is 70 mL.
How do you calculate the ejection fraction?
This is the percentage of blood that is ejected from the ventricle each cardiac cycle. This is calculated by; EF = SV/EDV. EF = 70 mL/130 mL It is normally ~60–65%.
Are the third and fourth heart sounds always pathological?
No, the third heart sound can be physiological in children, athletes and pregnant
women. However, the fourth heart sound is pathological.
During exercise, which part of the heart cycle reduces the most (systole or diastole)? What effect does this have on coronary artery filling?
Proportionally diastole decreases more.
This means that there is less time for left coronary artery filling as this occurs
most rapidly throughout diastole.
Which ventricle ejects blood first (the right or the left)
The right ventricle. This is because the pulmonary circulation is a lower pressure
system than the systemic circulation so the pulmonary valve opens before the
aortic valve.
what causes the ‘c’ wave on the JVP waveform?
ventricular contraction as the tricuspid valve bulges into the right atrium against a closed pulmonary valve.
when does the aortic valve open?
When the pressure inside the ventricle exceeds the aortic pressure, the aortic
valve opens.
what are the four componenets of ventricular diastole?
(1) Isovolumetric relaxation and
(2) Rapid inflow
(3) Diastasis
(4) Atrial
contraction;
what is the a wave of the VAP represent in the cardiac cycle?
the artial kick
what is the third heart sound?
Third HS: Oscillation of blood between the walls of the ventricles caused by the
inflow of blood from the atria. Heard at the beginning of the middle third of
diastole. Normal in youth, athletes and pregnant women. If heard in adults, it
may indicate heart failure
what does a 4th heart sound indicate?
Fourth HS: Contraction of the atria in late diastole pushing blood into a stiff or
hypertrophic ventricle. Always pathological.
what is the V wave in the JVP representative of in the cardiac cycle?
v’ wave is from ↑ in Rt atrial pressure just before AV valves open caused by
atrial filling
- List some features of cardiac muscle cells.
(a) Striated muscle
(b) Form a syncytium
(c) Connected by intercalated discs
(d) Gap junctions that allow the action potential to propagate from cell to cell
(e) T tubules
What fuel sources do the cardiac muscle cells use?
They predominately use fatty acids. At rest, 60% fatty acid, 35% carbohydrate
and 5% ketones and amino acids.
What is the resting membrane potential (RMP) of the cardiac muscle cell?
Sinoatrial (SA) node?
The cardiac muscle cells have a lower RMP than in the conducting system e.g.
SA node. The RMP in the cardiac muscle cells is −90 mV in comparison with
−60 mV in the SA node.
Describe the changes in the membrane permeability to ions during the different
phase of the cardiac action potential in cardiac muscle cells.
(a) Phase 0- Initial depolarisation due to rapid ↑ in Na+ permeability
(b) Phase 1- Initial repolarisation is due to inactivation of fast Na channels and
outward flow of K+ ions
(c) Phase 2- Inward current due to influx of Ca2+ → plateau phase
(d) Phase 3- Inactivation of slow Ca2+ channels hence there is unopposed
outward flow of K+ ions → repolarisation
(e) Phase 4- Restoration to the RMP. Cell membrane is most permeable to K+
Which part of the electrical conduction system of the heart transmits at the fastest speed?
The Purkinje fibres, 4 ms−1
.
How does the parasympathetic nervous system (PSNS) act to slow the heart rate?
It acts on the SA node. The acetylcholine (Ach) binds to muscarinic (M2)
receptors and via G-proteins opens K+ channels. This causes further movement
of K+ out of the cell and therefore hyperpolarizes it. This means it is harder for
the SA node to reach threshold potential and the heart rate is slowed.
How do you calculate the QTc and what part of the cardiac electrical cycle does
this represent?
The QT interval corresponds to electrical systole. The QT length is inversely
proportional to the HR
What ECG changes are seen in hypokalaemia and hyperkalaemia?
Hypokalemia causes prolongation of the PR interval, U waves, T wave
inversion/flattening and ST segment depression
• Due to prolonged ventricular repolarisation
• Later you may see prolonged segments
(b) Hyperkalemia may get peaked T waves, prolonged PR and QRS intervals
How does digoxin work? What are some ECG changes seen in digoxin toxicity?
Its primary mechanism is to inhibit the Na/K ATPase in the myocardium. In
toxicity ECG changes include T wave inversion or biphasic T waves.
how does the sympathetic nervous system act on the SA node to ↑ HR
and ↑ rate of conduction through AV node as well as ↑ force of contraction.
NA → B1 receptors → ↑ in cAMP → increased sarcolemma permeability to
Na+ and Ca2+ channels
Threshold is reached quicker
What three factors determine the stroke volume?
(a) Degree of filling of the ventricle, or “preload”
(b) Contractility of the myocardium
(c) Resistance against which the ventricle has to work, or “afterload”
Why does increasing the venous return, increase the cardiac output.
This is because of the Frank-Starling mechanism (Fig. 3.10). Increased venous return
increases the end diastolic volume (EDV) → This in turn increases the pre-contraction
length of the myocytes. This results in more optimal alignment of the actin and
myosin filaments and therefore a stronger contraction and greater stroke volume.
Name some negative inotropic agents.
A negative inotrope is any agent that decreases the contractility of the heart. The
most important physiological factor is the PSNS. Other pathological conditions
such as hypoxia, hypercapnia, acidosis have negative inotrophic effects on the
heart. Pharmaceutical agents such B-blockers, Ca2+ blockers, barbiturates and
many anaesthetics.
At rest, what percentage of oxygen is extracted from the coronary circulation?
~70%. This means that the increase oxygen needed during exercise is met with
increasing blood flow, controlled by local factors, namely hypoxia.
Name the four categories of shock.
(a) Hypovolemic
(b) Distributive
(c) Cardiogenic
(d) Obstructive
