Topic list 2 Flashcards
AP duration in myocytes
t= 200-400ms
AP conduction velocity in myocytes
v= 1m/s
What is the cardiac vector?
The vector sum of all cardiac electrical activity at any moment
Usual duration of PR/PQ interval
0.12-0.2 seconds
Usual duration of QRS interval
0.06-0.1 seconds
Usual amplitude of QRS interval
0.5-2mV
Usual duration of QT interval
0.36-0.4 seconds
What is the electrical axis of the heart?
It is the mean direction of the action potentials traveling through the ventricles during ventricular depolarization
How does unipolar recording work?
Two limbs are connected through electrical resistances to the negative terminal and the third limb is connected to the positive terminal
What is the isoelectric method for finding the electrical axis of the heart? (2)
- find the lead where QRS is isoelectric (usually III or aVL) and find the perpendicular to that : it’s the electrical axis
- In the perpendicular, look at R + or - to determine the direction of the axis
What is the EDV value?
About 130-140mL
What is the ESV value?
About 60mL
What is the ejection fraction?
SV/EDV
What is the usual range for the ejection fraction?
0.5
What is the usual max dp/dt?
1000-1200 mmHg/s
What are cardiac glycosides?
drugs that inhibit the Na+/K+ ATPase on the outer cell surface
What is the value of CO at resting conditions?
5600mL/min
What happens under steady-state conditions to CO?
It must then be equal to venous return
What is the CI?
it is a haemodynamic parameter that related the cardiac output from the left ventricle in one minute to the body surface area.
What is TPR?
total peripheral resistance : the ratio of the arteriovenous pressure difference to the flow through the entire systemic circulation (essentially CO)
What are the 3 ways of increasing preload?
- Increasing EDV
- Increasing filling time
- Frank Starling law
What are the 3 ways of increasing venous return?
- muscular milking
- by breathing (respiratory pump due to lower thoracic pressure than abdominal),
- sympathetic system stimulation : NE stimulates muscle constriction.
What is the Frank Starling law?
When you increase the stretch of the heart, it allows for more cross-bridges to be active. So greater stretch means greater force of contraction.
What is the afterload?
The amount of resistance to overcome for the left ventricle to eject blood into the aorta
What are 3 ways to increase the afterload?
- increasing peripheral resistance, which increases the pressure in the aorta
- if there’s sclerotic sections, blockage
- high blood pressure
What does the ESPVR describe?
The maximum pressure that can be developped by the left ventricle at any given volume
What are 4 things that affect contractility that get phosphorylated by PKA when NE/E binds to the B1 AR?
- L type VDCC
- Troponin I
- Phospholamban (PLB)
- Ryanodine receptor
What are the 3 techniques for determining CO?
- Fick’s principle
- Dilution technique
- Thermodilution technique
What are the 4 parts of microcirculation?
- Terminal arterioles
- Metarterioles
- Capillaries
- Venules
What are the 4 types of capillaries?
- Fenestrated
- Tight
- Continuous
- Sinusoidal
What keeps the RBCs from touching the endothelial wall at all times?
The glycocalyx inner covering of the capillary endothelium
What is the Bayliss effect?
The intrinsic capability of a body part to maintain a constant blood flow despite changes in perfusion pressure
What are the 3 types of mechanisms responsible for autoregulation?
- Metabolic
- Myogenic
- Endothelial
Which 6 metabolites can cause functional hyperemia?
- adenosine
- CO2
- K+
- H+
- Lactate
- Pi
What is nitric oxide synthesized from?
arginin and O2 by no synthase
What is the frequency for SA node?
100
What is the frequency for AV and bundle of His?
40-60
What is the frequency for bundle branches / purkinje?
20-40 (so low it can’t even pump properly)
What is the special property of the pacemaker cells?
Automaticity : they spontaneously depolarize and generate an AP
Which channel is involved for If current?
HCN4 (hyperpolarization activated cyclic nucleotide gated)
What activates this HCN4? (2)
- Hyperpolarization < -50 mV
- increase in cAMP
What activates T-VDCC channel?
Reaching the -55mV threshold
What drug can inhibit the If?
ivabradine
What can inhibit the T channels?
verapamil
What channel does IK1 use?
inwardly rectifying K channel (IRKC)
What is IKTO?
Transient outwards potassium current
What drug can inactivate the gNa?
lidocaine
Which drug can inactivate L-type VDCC?
dihydropopiridine
At what potential does early repolarization happen?
20mV
What are the 3 main causes of functional hyperemia in the heart?
- Adenosine
- O2
- K+
What are the causes for releasing adenosine in functional hyperemia? (2)
- insufficient coronary blood flow
- fall in myocardial pO2
What are the 4 ways of affecting short term local control of circulation?
- Myogenic mechanism (Bayliss)
- Metabolic mechanism (Bayliss)
- Shear stress effect
- Humoral regulation
What is the effect of decreased pO2 / increased pCO2 in the parenchyma? (3)
Decreased pH
Decreased adenosine
Increased lactate
What is the effect of decreased pO2 / increased pCO2 in the smooth muscle cell? (2)
Decreased ATP
Increased K+ (hyperpolarization)
What is the effect of decreased pH on the SMC?
Increased K+ (bc channels work well ig) int he cell, so decreased Em, so harder to make it contract
What is the effect of NO?
Activates soluble guanylyl cyclase in VSMCs to increase cGMP, which will cause vasodilation by decreasing myofilaments affinity to Ca2+
What are the end products of the cascade triggered by Renin? (3)
Angiotensin II, ADH, aldosterone
How much lymph is produced per hour?
120mL/hour
How much lymph is filtrated per day?
20L/day
How much lymph is reabsorbed per day?
16-18L /day
How much of the total blood volume do the veins contain?
About 65% of the total blood volume
What are the 3 main differences between the slow and fast response AP?
- value of RMP
- nodal tissue: resting pot keeps changing
- Myocardial AP is longer than nodal and both are longer than neuronal
What are the 5 ion currents involved in the generation of AP?
- Funny current (Na)
- Ica,t
- Ica,L
- Ik
- Ik, ach (inward rectifying)
Which channel is involved for If current?
HCN4 (hyper polarization activated cyclic nucleotide gated)
What activates HCN4? (2)
- Hyperpolarization under -50mV
- cAMP
What activates T-VDCC channel?
-50mV potential threshold
What drug can inhibit the If?
Ivabradine
What can inhibit the T channels?
verapramil
Which drug increases HR?
Atropine
What is inotropy?
Any effect that tries to increase contractility of the heart
What 4 things is contractility dependent on?
preload, nervous system, hormones, ions
What is the typical flow in a capillary when 1/4th are open?
About 8pL/s
What is compliance?
The ability to distand / increase in volume with an increase in transmural pressure
Which receptor does adenosine bind to in the heart?
gi coupled A1 receptor
What are the 3 major endothelial vasoactive substances?
endothelin, NO, prostacyclin
What are the 2 stages of formation of CSF?
ultrafiltration of plasma and secretion into the ventricles
What are the 4 types of capillaries?
- Continuous capillaries
- Fenestrated capillaries
- Sinusoidal capillaries
- Tight capillaries
What are the 3 types of forces that participate in venous return?
- Vis a tergo
- Vis a latere
- Vis a fronte
Which type of innervation is dominant in regulation of venal blood flow?
sympathetic innervation by releasing catecholamines
