Physiology (CVS) Flashcards
What are the factors affecting myocardial oxygen supply?
- Coronary blood flow
- Arterial oxygen content
What are the factors affecting coronary blood flow?
- Coronary perfusion pressure
- Coronary patency
- Coronary diameter
- Blood viscosity
- HR
Factors affecting coronary diameter?
- Autoregulation
- local metabolites & arterial gas tension
- Drugs
Factors affecting arterial oxygen content ?
- Hb concentration
- Arterial oxygen content
- Oxygen saturation
- Presence of abnormal Hb
Factors affecting myocardial oxygen demand ?
- Contractility
- Tissue mass (Increased with hypertrophy)
- Temperature
- Afterload
- HR
How can you measure coronary blood flow and cardiac output ? (Invasive)
- Fick’s principle
- Coronary angiography
- Thermodilution
- Transoesophageal echo
- Trans-thoracic echo
Describe the Fick’s principle?
- It can be used to measure flow in all organs
- It states that substance taken by an organ is equal to blood flow to that organ and the arterio-venous difference of the substance
- Argon & oxygen can be used
What is the equation for coronary blood flow?
Coronary blood flow = Uptake of substance arterial - venous difference
CO = VO2 / PaO2 - PvO2
What is the doppler effect?
Changed in the frequency of sound if their transmitter or receiver is moving.
It can be used to measure cardiac output by knowing the cross-sectional area of the aortic arch
What are the different types of action potentials ?
- Cardiac AP
- Pacemaker AP
- Peripheral nerves AP
Draw a diagram of the cardiac muscle AP?
See diagram
Describe the phases of cardiac muscle AP?
Phase (0)
- Rapid depolarization after TP reached
- Sodium influx
- Vertical gradient
Phase (1)
- Re-polarization
- Sodium channels closing
- Potassium channels opening
- Short phase
Phase (2)
- Plateau phase
- Opening of L-type Calcium channels
- Depolarization maintained
- No further depolarization if possible
- This is the absolute refractory period
- Repolarization is slowed but not stopped
Phase (3)
- L-type calcium channels close
- Potassium efflux & repolarization occurs
- Relative refractory period
Phase (4)
- Na/K pump restores ionic gradients
- 3Na out & 2K into the cell
Why is tetany not possible in myocardial muscles?
- Phase (2) of cardiac muscle AP
- Opening of L-type calcium channels
- Off-set of the effect of potassium
- No further depolarization is possible
When does the relative refractory period occur in cardiac muscles?
During phase 3 & 4
Phase of pacemaker AP?
Phase (0)
- TP achieved at -40mV
- Open L-type Ca channels + Depolarization
- Slow calcium influx
Phase (3)
- Repolarization + Closing of Ca channels
- Opening of Potassium channels + Efflux
Phase (4)
- Hyperpolarization
- Drift towards threshold potential (TP)
- Sodium leak
- Opening T-type Ca channels
- Activation of Na/Ca pumps
Factors affecting phase (4) of pacemaker AP?
- Sympathetic stimulation - Increased gradient
- Parasympathetic stimulus - Decreased gradient
Phases of nerve action potential ?
Phase (1)
- Crosses the y-axis at -70mV
- Reaches threshold potential at -55mV
Phase (2)
- Rapid rise of membrane potential to +30mV
- Opening of voltage-gated Na channels + influx of Na
Phase (3)
- Rapid repolarization + closure of Na channels
- Potassium channels open + efflux
Phase (4)
- Hyperpolarization
- Na/k pumps restore ionic balance
Review the diagram of all the combined action potentials
See image
Draw of graph of the cardiac cycle superimposed on the ECG
See attached image
What is the value of normal CVP?
5-10 mmHg
Components of CVP trace?
C-wave:
- Isovolumetric contraction
- Bulging of tricuspid valve to the RV
Y-wave:
- Occurs after isovolumetric relaxation
- Tricuspid valve opens
What is the explationation for dicrotic notch on ECG?
- IVR
- Closure of the aortic valve
- Back flow of blood just before aortic closure
- Bulging of the sinus of valsalva
What do the heart sounds signify?
HS1
- Closure of mitral & tricuspid valves
- Occurs at the beginning of systole
- Matches IVC
HS2
- Closure of aortic and pulmonary valves
- Occurs at the start of diastole
- Matches IVR
Cardiac cycle sequence?
Start of IVC:
- Depolarization + Contraction
- LV pressure rises above CVP
- Mitral valve closes (S1)
End of IVC:
- LV pressure rises above aortic pressure
- :Aortic valve opens
Start of IVR:
- LV pressure falls below aortic pressure
- Aortic valve closes (S2)
End of IVR:
- LV pressure falls below CVP
- Mitral valve opens
- Ventricular filling occurs
LV pressure wave form and ECG?
Image attached
What are the typical values on an LA pressure wave form?
a-wave = 4-16 mmHg
v-wave = 6-21 mmHg
MAP = 2-12 mmHg
Define the pressure waves on LAP wave form?
A-wave
- Atrial systole
C-wave
- Coincides with ventricular contraction
- Caused by AV valve bulging into the atrium
V-wave
- Pressure build up due to venous return
- AV valve open
X-descent
- Decline in pressure between C & V waves
- Pulling down of the atrium + RV contraction
Y-wave
- Decline in atrial pressure as AV valve open
Causes of prominent C & V wave on LAP wave form?
- Incompetent AV valves
- X-wave is abolished
Draw the frank-sterling relationship?
The strength of cardiac muscle contraction is dependent on initial length
What is ANP?
- Brain natriuretic peptide
- Cytokines natriuretic peptide
Characteristic of ANP?
- Produced by cardiac myocytes atrial wall
- Triggered by increased volume & stretch
- Increases Sodium excretion
- Inhibits Na reabsorption from collecting duct
- Induced diuresis & decrease ECV
- Caused arterial vasodilation
What is BNP?
- Brain natriuretic peptide
- Located in the brain ventricle
- Secreted in response to increased ECF
- It is usually 20% of the value of ANP
- Elevated in CCF - > ANP
What is the formula for SVR ?
SVR = MAP - MRAP / CO x 80
MAP = Mean arterial pressure
MRAP = Mean right arterial pressure
CO = Cardiac output
What is the formula for PVR?
PVR = MPAP - PCWP / CO x 80
MPAP = Mean pulmonary arterial pressure
PCWP = Pulmonary capillary wedge pressure
CO = Cardiac output
What is the normal PVR & SVR value ?
PVR = 50-150 dyne/sec/cm-5
SVR = 700-1500 dyne/sec/cm-5
What is the normal value for EDV (End diastolic volume)?
120mls
What is the normal value for diastolic aortic pressure?
80 mmHg
What is the normal SV?
70 mls
Draw a cardiac pressure volume loop?
See attached image
both vertical lines represents IVC & IVR
Calculate work of ventricle?
work = pressure x volume
What is the formula for calculating ejection fraction ?
EF = EDV - ESV / EDV x 100
EDV - ESV = SV
Demonstrate the effect of increased pre-load by diagram?
- Increasing preload increases SV
Demonstrate the effect of increased after-load by diagram?
See image
Demonstrate CCF on a pressure volume loop?
See image attached
Factors affecting the pressure volume loop and thus diastolic function/
- Compliance
- Distensibility
- Relaxation
Describe the valsalva manoeuvre ?
Blowing against a closed glottis for 10s
Describe the phases of valsalva manoeuvre?
Phase (1)
Onset & short in duration
Increased thoracoabdominal pressure
Increased venous return
Increased BP & decreased HR
Phase (2)
Continues until the end of manoeuvre
Sustained rise in intrathoracic pressure
Reduced venous return
Fall in SBP + Cmpensatory tachycardia
Phase (3)
Begins as soon as manoeuvre is completed
Release of pressure
Large venous return vaccum
Fall in BP + Sustained tachycardia
Phase (4)
Continues until restoration normal values
Tarchycardia + Restoration of BP / VR
Reflex bradycardia occurs
What are the innervation of the receptors of the valsalva manoeuvre?
Aortic arch baroreceptor - Vagus nerves
Carotid baroreceptors - Glossopharyngeal
Response to sudden drop in BP?
- Baroreceptor reflex activation
- Redistribution of cardiac output
- Activation of renin-angiotensin aldosteron
- Increased ADH secretion
What are starling forces?
- Movement of fluid into the IV compartment
- Decreased hydrostatic pressure
- Increased oncotic pressures
What is the Bain Bridge reflex ?
Atrial baroreceptor activation in response to hypovolaemia
Sensitivity and specificity of the cardiac stress test ?
Specificity = 90%
Sensitivity = 65%
What are the factors associated with severe cardiac disease?
- Early ST-segment depression > 2mm
- ST-depression > 5mins
- Decreased BP > 10% of baseline
- Failure to increase HR > 70% of baseline
- Ventricular arrhythmias
