Cardiology physiology Flashcards
What volume of blood is present in circulation in an average 70kg man?
5.5L
How can arteries dampen the pulsatile oscillations in pressure that result from intermittent outflow of blood from the left ventricle?
As they are elastic
Smaller arteries and arterioles are the primary vessels involved in what?
Regulation of arterial blood pressure and blood flow within organs
Smaller arteries and arterioles are innervated by what?
Autonomic nervous system
What are the primary exchange vessels in the body?
Capillaries
What are the main differences between arteries and veins?
Veins are larger in diameter
Veins provide less resistance
Vein walls are thin and distensible
What percentage of blood volume is contained within veins?
70%
Why are veins known as capacitance vessels?
Because veins act as a blood volume reservoir
What are the 3 layers of large and medium sized arteries?
Tunica intima
Tunica media
Tunica adventitia
What is the tunica intima composed of?
Thin layer of endothelial cells
Sub endothelium connective tissue
Elastic lamina
What is the tunica media composed of?
Fenestrated elastic membranes
Smooth muscle cells
Collagen
What is the thickest part of arterial walls?
Tunia media
What is the tunica adventitia composed of?
Thin layer of connective tissue
Lynphatics
Nerves
Vasa Vasorum (blood vessels that supply smooth muscle)
Arteries with a diameter less than what are classed as arterioles?
<0.1mm
What are the walls of capillaries made up on?
Single endothelial cells
What are the 3 main types of capillary?
Continunous
Fenestrated
Sinusoidal
Which vessels are the preferred site of white blood cell migration I inflammation and infection?
Veins
What do most vasoconstrictors bind to and cause?
Receptors that cause a G-protein mediated rise in intracellular calcium levels = contraction of vascular smooth muscle.
Where does intracellular calcium arise from?
Sarcoplasmic reticulum
Entry across sarcolemma through calcium channels
Name some vasoconstrictors.
Endothelin-I
Angiotensin-II
Noradrenaline
What do calcium channel blockers do?
Prevent or reduce opening of calcium channels = reduction in vasoconstriction.
How do most endogenous vasodilators cause vessel relaxation?
By increasing cGMP (E.G. NO) or cAMP (prostacyclin/ beta agonists)
Removal of which ions causes vasodilation?
Calcium ions
Which aspect of vessels plays an important role in regulation of vascular tone?
Vascular endothelium (as it is a source of important vasoactive mediators)
Nitrous oxide production is increased by what?
Factors that increase intracellular calcium levels (bradykinin, histamine, serotonin)
What is the normal value of cardiac output in an adult?
5-6L/minute at rest
More than 35 L/minute for elite athletes during exercise
How is cardiac output defined?
Stroke volume x heart rate
What is stroke volume?
The amount of blood expelled from the heat with each beat.
What is the normal value of stroke volume in an adult?
50-100ml
Define mean arterial pressure (MAP).
The average arterial pressure during a single cardiac cycle.
What is the normal range for MAP?
65-110 mmHgW=
What is the minimum that MAP must be in order for adequate oxygen perfusion to occur?
65mmHg
MAP is considered a better indicator of vital organ perfusion that what?
SBP
How is MAP calculated?
DBP + 1/3rd pulse pressure
OR
DBP + ((SBP-DBP)/3)
When calculating MAP, who does diastole count for more than systole?
Because 2/3rds of the cardiac output is spent I diastole.
What is pulse pressure?
The difference between SBP and DBP,
What does pulse pressure measure?
The force generated by the heart each time it contracts.
What is the usual resting pulse pressure in healthy adults?
30-40mmHg
Name the causes of a narrow pulse pressure.
Reduced CO (blood loss)
Aortic stenosis
Cardiac tamponade
CCF
Name the causes of a wide pulse pressure.
Atherosclerosis
Aortic regurgitation
AV malformation
Aortic root aneurysm
Aortic dissection
Hyperthyroidism
Where is central venous pressure recorded?
RA or SVC
When should CVP be measured?
With the patient lying flat at the end of expiration.
What is CVP a useful indicator of?
Right ventricular preload
Name factors that can increase central venous pressure.
Hypervolaemia
Forced exhalation
Tension pneumothorax
Heart failure
Pleural effusion
Decreased CO
Cardiac tamponade
Mechanical ventilation
Pulmonary hypertension
Pulmonary embolism
Name factors that can decrease central venous pressure
Hypovolaemia
Deep inhalation
Distributive shock
Negative pressure ventilation
What are the 5 components of the CVP waveform?
A wave
C wave
V wave
X descent
Y descent
Which phase of the cardiac cycle is represented by the A wave?
End diastole
Which phase of the cardiac cycle is represented by the C wave?
Early systole
Which phase of the cardiac cycle is represented by the V wave?
Late systole
Which phase of the cardiac cycle is represented by the X descent?
Mid systole
Which phase of the cardiac cycle is represented by the Y descent?
Early diastole
What is the mechanical event represented by the A wave?
Atrial contraction
What is the mechanical event represented by the C wave?
Closing and bulging of tricuspid valve.
What is the mechanical event represented by the V wave?
Systolic filling of the atrium.
What is the mechanical event represented by the X descent?
Atrial relaxation.
What is the mechanical event represented by the Y descent?
Early ventricular filling.
What does Einthoven’s law state?
That the voltage in lead II on an ECG is the sum of the voltages in leads I and III.
What do the leads of an ECG detect?
Depolarisation as electrical current moves through the heart.
Which leads form Einthoven’s triangle?
Right arm
Left arm
Left leg
What prevents direct spread of depolarisation from the atria to the ventricles?
Annulus fibrosis
Repolarisation is achieved by influx of which ion?
K+
What is the Treppe effect?
When an increase in heart rate causes an increase in contractility.
Where are baroreceptors located?
Aortic arch and carotid sinus
What is the resting membrane potential of SAN cells?
-60 mV
Endothelin 1 is stimulated by which substances?
Noradrenaline
Angiotesin-II
ADH
Hypoxia
Nitrous oxide production is stimulated by which factors?
Shear stress (increased blood flow)
Bradykinin
Histamine
Serotonin
Substance P
What causes the plateau phase of the cardiac action potential cycle?
Opening of voltage gated slow L-type Ca2+ channels
Where are continuous capillaries found?
Skin
Fat
Muscle
Nervous tissue
The Frank-Starling curve shows the relationships between…
Stroke volume and end diastolic volume
Where are sinusoidal (discontinuous) capillaries found?
Bone marrow
Liver
Spleen
What are the 5 stages of the cardiac cycle?
Early diastole
Atrial systole
Isovolumetric ventricular contraction
Ventricular ejection
Isovolumetric ventricular relaxation
What happens during early diastole?
Whole heart relaxed
Ventricles filling passively
What happens during atrial systole?
Atria contract
Final phase of ventricular filling
EDV established
What happens during isovolumetric ventricular contraction?
Ventricular myocytes begin to contract
Ventricular pressure increases
Ventricular volume is constant
What happens during ventricular ejection?
Ventricles contract fully
Aortic pressure increases
Ventricular volume at minimum
What happens during isovolumetric ventricular relaxation?
Ventricles relax
Ventricular volume is constant
Atria expand and fill
During early diastole, what are the valves doing?
AV valves open
SL valves closed
During atrial systole, what are the valves doing?
AV valves open
SL valves closed
During isovolumetric ventricular contraction, what are the valves doing?
Both valve pairs closed
During ventricular ejection, what are the valves doing?
AV valves closed
SL valves open
During isovolumetric ventricular relaxation, what are the valves doing?
Both valve pairs closed
What creates S1?
Closure of mitral and tricuspid valves
What creates S2?
Closure of aortic and pulmonary valves
When can S3 occur?
Early diastole
What are the causes of an S3 being present?
Heart failure
**Can occur in children + young adults
When does S4 occur?
Late diastolic filling
What are the causes of S4?
Increased resistance to filling (stiff ventricular wall)
What conditions can an S4 heart sound be associated with?
Ventricular hypertrophy
Aortic stenosis
Post-MI ventricular fibrosis
Hypertrophic cardiomyopathy
Restrictive cardiomyopathy
On an ECG, what is early diastole represented by?
Iso-electric line
On an ECG, what is atrial systole represented by?
P wave + PR interval
On an ECG, what is isovolumetric ventricular contraction represented by?
QRS complex
On an ECG, what is ventricular ejection represented by?
ST segment
On an ECG, what is isovolumetric ventricular relaxation represented by?
Iso-electric line
S1 occurs during which stage of the cardiac cycle?
Isovolumetric ventricular contraction
S2 occurs during which stage of the cardiac systole?
Isovolumetric ventricular relaxation
S3 can occur during which phase of the cardiac cycle?
Early diastole
S4 can occur during which phase of the cardiac cycle?
Atrial systole
Define cardiac output.
The volume of blood pumped by the heart in 1 minute.
How is cardiac output calculated?
CO = SV x HR
Define stroke volume.
The amount of blood pumped from the left ventricle per beat.
How is stroke volume calculated?
Volume at end of diastole - volume at end of systole.
What is central venous pressure?
The blood pressure in the vena cava in close proximity to the right atrium.
What does Starling’s law represent?
The relationship between stroke volume and end diastolic volume.
What does Starling’s law state?
The stroke volume of the heart increases in response to an increase in end diastolic volume, before the contraction when all other factors remain constant.
The greater the end diastolic volume, the greater the strength of the muscle fibre (sarcomere) length, the grater the contractility.
What does a decrease in inotropy do to the starling curve?
Shifts it down and to the right = smaller SV.
What does an increase in inotropy do to the starling curve?
Shifts it up and to the left = larger SV.
What is the most important consequence of starling’s law?
That the stroke volumes of the right and left ventricles are matched.
According to starling’s law, if output from the RV was greater than output from the LV, what would happen?
Bloods would accumulate in the lungs = pulmonary blood pressure would rise = pulmonary oedema.
Which 3 factors influence stroke volume?
Preload
Contractility of the heart
Afterload
What is preload?
The amount of stretch of the myocardium at the end of diastole.
What is after load?
The pressure against which the heart has to pump.
How are inotropic effects normally achieved?
Through alteration of free calcium ion concentration.
Give an example of a negative inotrope.
Acidosis (raised H+ concentration competes with Ca2+ for intracellular binding sites).
Give 2 examples of positive inotropes.
Cardiac glycosides
Sympathetic stimulation
What is the effect of an increased after load on the starling curve?
Shifts it down and to the right.
What is the effect of a decreased after load on the starling curve?
Shifts it up and to the left.
Which receptors detect CVP upon standing?
Baroreceptors
What is the point of origin of electrical impulses in the heart?
SAN
Where is the SAN?
Right atrium at junction with SVC.
At what rate does the SAN generate electrical impulses under normal conditions?
60-100 times per minute.
Where is the AVN located?
Right atrium at posteroinferior area of intratrial septum.
What slows down the electrical impulse between the atria and the ventricles?
Annulus fibrosis
How often does the AVN generate impulses?
40-60 times per minute.
How often do the purkinje fibres generate impulses?
20-40 times per minute.
How many phases are there in the cardiac action potential?
5 (0-4)
What is phase 0 of the cardiac action potential?
Rapid depolarisation phase
What is phase 1 of the cardiac action potential?
Early depolarisation phase
What is phase 2 of the cardiac action potential?
Plateau phase
What is phase 3 of the cardiac action potential?
Rapid depolarisation phase
What is phase 4 of the cardiac action potential?
Resting phase
When is a cardiac action potential triggered?
When the membrane potential reaches -70mV
What is the main movement of ions responsible for the rapid depolarisation?
Rapid influx of Na+ through fast Na+ channels.
When do L-type Ca2+ channels open?
Phase 0 (rapid depolarisation phase)
When does phase 1 (early depolarisation phase) begin?
Once Na+ channels inactivate.
What is the mainstay of ion movement in phase 1 (early depolarisation phase).
Efflux of K+ and Cl- ions
What happens in phase 2 (plateau phase) of the cardiac action potential.
Slow influx of Ca2+ via L-type Ca2+ channels that opened in phase 0.
AND
Efflux of K+ ions via delayed rectifier channels.
How is the plateau in phase 2 of the cardiac action potential sustained?
A balance between movement of calcium ions in and potassium ions out of the myocytes.
When do L-type Ca2+ channels close?
Phase 3 (rapid depolarisation)
What happens during phase 3 (rapid depolarisation) of the cardiac action potential?
Further efflux of K+ via already open K+ channels.
What happens in phase 4 (resting phase) of the cardiac action potential?
Resting potential is restored by Na+/K+ ATPase and Na+/ Ca2+ exchanger
What is the resting potential of the cardiac membrane?
-90mV
About how long does the cardiac action potential last?
~200ms
What does an ECG ‘lead’ show?
A view of the heart’s electrical activity from a particular angle across the body.
Which ECG leads view the heart from a horizontal place?
Chest leads
Which ECG leads view the heart from a vertical plane?
Limb leads
Which ECG leads look at the right ventricle?
V1-V2
Which ECG leads look at the septum?
V3-V4
Which ECG leads look at the anterior and lateral walls of the left ventricle?
V5-V6
How much time is represented by 1 small square on an ECG?
0.04 seconds
How much time is represented by a large square on an ECG?
0.2 seconds (5 small squares)
What does the p wave on an ECG correspond to?
Atrial depolarisation
What does the QRS complex on an ECG correspond to?
Ventricular depolarisation
What does the T wave on an ECG correspond to?
Ventricular depolarisation
How long is the QRS complex under normal conditions?
0.12 seconds (3 small squares)
If the QRS complex is <0.12 seconds, where does the rhythm originate from?
Above the bifurcation of the BoH (the rhythm is supra ventricular and originates from the SAN, AVN or atria).
If the QRS complex is >0.12 in length then where does the rhythm originate from?
Ventricular myocardium or supraventricular with aberrant conduction
What is the normal QRS axis?
Between -30 and +90 degrees
What are the deflections of lead I and aVF in a normal axis?
Both positive
What are the deflections of lead I and aVF in a left axis deviation?
Lead I = positive
aVF = negative
What are the deflections of lead I and aVF in a right axis deviation?
Lead I = negative
aVF = positive
What are the deflections of lead I and aVF in extreme axis deviation?
Both negative
What are the causes of LAD?
Normal (physiological axis deviation)
LVH
LBBB
Inferior MI
WPW syndrome
What are the causes of RAD?
Right heart strain (PE)
RVH
RBBB
Lateral wall MI
WPW syndrome
What duration should a normal p wave last for?
<120ms (3 small squares)
In which leads is it normal for aa t wave to be inverted?
V1
aVR
Lead II
What does the PR interval represent?
Conduction from AVN to bundle branches and purkinje fibres
How long should the normal PR interval be?
0.12 - 0.2 seconds (3-5 small squares)
How long should a normal QT interval be?
<440ms
Name metabolic disorders that can cause a prolonged QT interval.
Hypothyroidism
Hypocalcaemia
Hypokalaemia
Hypomagnesaemia
Hypothermia
Name drugs which can cause a prolonged QT interval.
Erythromycin
Quinidine
Amiodarone
TCAs
Terfenadine
Sotalol
Methadone
Procainamide
Name structural heart problems that can cause a prolonged QT interval.
IHD
Mitral valve prolapse
Rheumatic carditis
Which systems exhibit good auto regulation?
Renal
Coronary
Cerebral
Which 2 mechanisms contribute to auto regulation?
Myogenic stretch response
Locally produced vasodilation factors
How does the myogenic stretch response work?
Increase blood flow or pressure = myocytes stretch = membrane depolarisation = L-type calcium channels activated = influx of calcium = vasoconstriction.
What are the most potent vasodilators in skeletal muscle?
K+
Adenosine
What are the most potent vasodilators in cerebral circulation?
CO2 and K+
Does hypoxia cause vasodilation or vasoconstriction?
Vasodilation
What is the earliest measurable sign of shock?
Tachycardia
Define the blood loss for the 4 categories of haemorrhage.
1 = Up to 750
2 = 750 - 1500
3 = 1500 - 2000
4 = >2000
Define the pulse rate for the 4 categories of haemorrhage.
1 = <100
2 = 100-120
3 = 120-240
4 = >140
Define the respiratory for the 4 categories of haemorrhage.
1 = 14-20
2 = 20-30
3 = 30-40
4 = >40
Define the SBP for the 4 categories of haemorrhage.
1 = normal
2 = normal
3 = decreased
4 = decreased
Which ion channels are not present in the SAN?
Fast Na+ channels
What causes depolarisation in the SAN?
Ca2+ influx via slow calcium channels
What permits the spread of depolarisation across the atria?
Gap junctions
What drives the self-generated automaticity of pacemaker cells?
The pacemaker potential
What determines the timing of the next action potential and the HR in cardiac myocytes?
The rate of decay of the pacemaker potential.
What does a u wave on an ECG represent?
Depolarisation of the inter ventricular septum.
Where does calcium originate from in myocytes?
Sarcoplasmic reticulum
