Lecture 5: Cardio Flashcards
What does the right heart pump to?
Pumps blood through the lungs
What does the left heart pump to?
Pump blood through the body
What are some key characteristics of cardiac myocytes?
There are specialized excitatory and conductive fibers.
Conduction is extended in a cardiac myocytes.
What is the SA node’s intrinsic heart rate?
60-100 bpm, but generally higher without ANS modulation.
What are the key anatomical differences in cardiac myocytes vs skeletal muscle?
Latticework
Functional syncytium made from intercalated discs.
What is a syncytium?
A combined cytoplasm, usually made by intercalated discs.
Where are the two syncytia of the heart?
Atrial and ventricular.
Note:
They are separated by an insulated fibrous layer in their AV valves to the signal does not pass through them. Signal goes via interventricular septum.
What are the two action potential related differences between skeletal and cardiac muscle?
Cardiac has two channels, fast sodium + calcium-sodium.
Calcium-sodium is slower to open and remains open for much longer (several tenths of a second).
Calcium for the muscle AP comes from the sarcoplasmic reticulum AND the T tubules.
What does the strength of contraction of a cardiac muscle fiber depend on?
ECF concentration of calcium.
What does beta-adrenergic stimulation of the heart do?
Increase cardiac contractility and acceleration.
Note:
Think of dobutamine, the beta-1 agonist we learned in pharm.
What does DHP stand for?
Dihydropyridine.
What class antiarrhythmic is amiodarone?
Class III, because it works on phase 3 of the cardiac AP.
This is the part of the phase that is dependent on potassium, so amiodarone affects potassium channels.
What part of the cardiac action potential does a calcium channel blocker (CCB) affect?
It is class IV, a non-DHP CCB.
It affects phase 2 of the cardiac AP, which is the plateau phase of the cardiac action potential. It slows electrical conductivity, extending the phase.
What is the slow depolarization of the SA node action potential known as?
Pacemaker potential
Explain the process of the SA node’s AP.
At -60 mV, K+ channels close, slow Na+ channels open.
Slow increase to -40. -60 to -40 is the pacemaker potential.
-40 is when Ca channels open , which goes to +5.
At the peak, Ca channels close and K+ channels open, reducing the membrane potential. As it repolarizes, the Ca permeability decreases at -10 and the K+ permeability increases at -30.
Note:
Above -40 is the AP, below -40 is the pacemaker potential.
What 3 things does parasympathetic innervation do to the SA node’s AP?
Reduces rate of depolarization.
Increase in the time it takes to repolarize.
Upward shift in threshold potential.
What does S1 represent?
AV valve closure.
What does S2 represent?
Semilunar valve closure.
When does isovolumic contraction occur between?
AV valve closure and semilunar valve opening.
When does isovolumic relaxation occur between?
Semilunar valve closure and AV valve opening.
What are EDV and ESV?
End diastolic volume = the volume at the end of diastole
End systolic volume = the volume at the end of systole.
EDV - ESV = SV, or stroke volume.
Where does the cardiac cycle begin?
SA node, located in the superolateral wall of the R atrium near the opening of the SVC.
What is diastole?
A period of relaxation when the heart is filling with blood.
What is systole?
A period of contraction.
How does blood flow into the ventricles during diastole?
Mainly gravity, with a minor amount of atrial contraction contributing.
What are the AV valves specifically designed to prevent?
Backflow of the blood from the ventricles to the atria
Note:
Think of their shape.
What are the semilunar valves specifically designed to prevent?
Backflow of the blood from the aorta and pulmonary trunk to the ventricles
Note:
Think of their shape
What does contraction of the chordae tendineae do?
Prevents the valves from bulging. It is NOT to help the valves close.
What is the increase of LV volume also known as?
Period of rapid filling of the ventricles.
Why does isovolumic contraction occur?
The AV valves close and volume stays identical, hence isovolumic. However, it takes .02-.03 secs to build up pressure to open the semilunar valves.
What is the pressure of the LV during systole?
Slightly above 80mm Hg.
What are the two parts of ejection?
Period of rapid ejection and slow ejection.
Rapid = 70%, during the first 1/3 of ejection.
Slow = 30%, during the 2nd 2/3 of ejection.
Why does isovolumic relaxation occur?
The ventricle begins relaxing, reducing pressure and closing the valves. Even with the valves shut, the ventricles are still relaxing back to normal.
What is ejection fraction?
The amount of blood the left ventricle ejects per stroke relative to its end diastolic volume.
Essentially, its how much of the blood in the left ventricle during contraction gets ejected out.
EF is therefore (SV/EDV) x 100.
What does S1 sound like?
Low in pitch, relatively long-lasting.
What does S2 sound like?
Rapid snap, with vibration after.
What does aortic stenosis look like on a phonogram?
It appears between S1 and S2 as a big constant vibration. This is because the narrow valve means all the blood goes through it in intervals.
What does mitral regurgitation look like on a phonogram?
Small vibrations between S1 and S2. This is because blood flowing back will stop the valves from closing fully.
What does aortic regurgitation look like on a phonogram?
Small vibrations after S2 all the way to S1. This is because blood flowing back will stop the valves from closing fully in the aorta.
What does a patent ductus arteriosus sound like?
Constant vibrations the whole time, no distinct S1 and S2.
hole between ventricles mixing blood
When is LV pressure greatest?
During systole, aka when the ventricle is contracting and is therefore at its highest volume. It will peak a little before it ejects the last 1/3 of its SV.
When is LV pressure lowest?
During diastole, aka when the ventricles are filling and relaxed.
What is the usual ESV? EDV?
ESV:50 mL
EDV: 120 mL
Explain the volume pressure curve for the left ventricle, beginning at the start of diastole.
LV volume & pressure are at minimum. Volume will increase as the mitral valve stays open, so blood from the atrium pours into the ventricle.
Once the ventricle is filled, its volume is maxed and the mitral valve closes. It begins to contract, increasing pressure without a volume change (Isovolumic contraction).
Once pressure exceeds the threshold, the aortic valve opens, and volume will rapidly decrease as the ventricle squeezes it into the aorta.
Once the squeeze is done, pressure is reduced and the aortic valve closes. The ventricle begins relaxing but volume does not change (isovolumic relaxation)
The cycle begins anew.
What is rate pressure product? Why is it significant?
RPP is used as a measure of myocardial work.
Of note, the heart consumes 70% of the oxygen from coronary arteries, which is 3x more than skeletal muscle. It can also increase its coronary blood flow up to 4x.
Note:
RPP increased for patients being trained before angina petoris and ST depression occurred in pts with heart disease.
How do I calculate RPP? Typical values?
RPP = HR X SBP (systolic blood pressure)
A regular HR of around 50 bpm and SBP of 120mmHg means work is around 6000 at rest.
A HR of around 200 bpm and a SBP of 200 mm Hg means work is around 40,000 at maximum exercise for example.
How is the stroke volume adjusted in the heart?
Intrinsic regulation by venous return and ANS modulation.
Describe Frank Starling’s mechanism.
Venous return is directly proportional to SV.
The greater the heart muscle is stretched while filling (diastole), the greater the force of contraction (systole)
AKA the more blood our veins send to our RA, the more we can eject from our LV.
Describe why more stretch causes more contraction.
The greater the stretch, the better the orientation between actin and myosin, which causes greater crossbridge action = more force.
What is preload? What affects it?
Preload, aka end diastolic filling volume.
It is affected by muscle pump (aka muscle contraction increases venous return)
Respiratory pump (reduced intrathoracic pressure causes blood to rise up from the lower body)
Venoconstriction by the SNS
Dynamic work (aka a runner constantly moving)
What is afterload? What affects it?
Afterload is the amount of pressure needed to eject blood out of the ventricles.
SBP
Aortic stenosis
Arteriosclerosis
Static work (aka a weight lifter lifting a weight slowly)
What can SNS and PNS do to the volume of blood we pump?
Sympathetic can increase HR to 180-200 in a young adult.
Force of contraction increases by 2x.
Increased SV
Increased ejection pressure.
therfore SNS can increase max cardiac output 2-3x in addition to increased output by frank starling mech
Where are SNS and PNS nerve fibers found on the heart?
PNS:(vagi)
by AV and SA nodes
A few to the atria, very little to ventricles via vagus nerves.
SNS:
All parts of the heart, but mainly ventricles.
If I depress the SNS, what usually happens to the heart?
Heart rate (chronotropic) and strength of ventricular contraction (Inotropic) decrease by around 30%, since the SNS is always sending a slow, continuous signal.
If I increase the PNS, what can happen to the heart?
It can stop for a few seconds.
Decreases heart contraction (inotropic) by up to 30%, but because the fibers don’t really go much to ventricles, HR is affected since its mainly atria affected, so the overall effect is HR reduction (chronotropic).
What is the Fick Equation? What is it used for?
VO2 = CO * a-VO2 diff, which is used to calculate CO from oxygen consumption
CO = HR * SV
What increases mainly in an athlete?
Stroke volume. HR also increases SLOWER but has the SAME MAX.
a-VO2 difference also increases much SLOWER in an athlete, as their max oxygen consumption is far greater.
What determines local blood flow control?
Tissues!
The amount of oxygen a tissue wants dictates how much blood flow it gets.
What 3 organs require most of our blood flow?
Liver: 27
Kidneys: 22
Brain: 14
How much can blood flow increase to muscles? How?
heavy exercise
metabolic activity increases 60 fold
20x increase in blood flow.
More capillaries
Bigger capillaries
(16,000 ml/min)
(80ml/min/100g muscle)
What is acute blood control achieved by?
rapid changes in vasoconstriction or dilation of Arteriole, metaarteriole, and pre-capillary sphincters.
Occurs within seconds to minutes.
What is long-term blood control achieved by?
Provide better control of flow in response to needs of tissues
Increases/decreases in capillaries.
Increases/decreases in capillary size.
Slow, controlled changes over days, weeks, months
What substances vasodilate?
Adenosine, CO2, Adenosine phosphate compounds, Histamine, Potassium ions, Hydrogen ions
What is the oxygen lack theory ?
Vessels need oxygen to make energy for vessels to constrict, so in the absence of oxygen, vessels will dilate.
What are the two structures in the kidney that affect acute blood flow?
Macula densa
Juxtaglomerular apparatus
What other molecules affect brain blood flow?
CO2 and H+, causing cerebral vessel dilation.
The brain’s level of excitability is highly dependent on CO2 and H+, so it needs to get rid of excess.
How is blood flow affected by the skin?
closely linked to regulation of body temperature
Cutaneous and subcutaneous blood flow regulates heat loss from body, since blood carries heat. It is controlled mainly by sympathetic nerves.
Where does Nitric Oxide come from? half life, wehre does it act
Endothelium, from the synthesis of arginine and oxygen by nitrix oxide synthase. It has a half-life of 6s and acts locally on tissue where it was released.
When is NO released and what is its effect?
When enodthelial cells experience shear stress, they get contorted and NO is released. This relaxes the blood vessel, dilating it.
It can also come from angiotensin II, which releases it to prevent excessive vasoconstriction, since angiotensin II is a vasoconstrictor.
What is the term we use for a tissue increasing its blood flow over time by getting bigger and more vessels?
Angiogenesis.
What does a hyper oxygenated environment cause?
For babies, it can stop vascular growth, specifically in the retina. Leaving the environment can cause explosive growth, leading to blindness since the tissue suddenly grows super fast.
Retrolental fibroplasia
What is BP a measure of?
BP = CO * TPR or SVR
TPR = total peripheral resistance
SVR = systemic vascular resistance
Both are interchangeable.
What is MAP?
Mean arterial pressure.
MAP = DBP + 1/3(SBP -DBP)
What is pressure a calculation of?
Pressure = flow * resistance.
Flow = CO
Resistance = TPR or SVR.
Pressure is therefore proportional to flow and resistance.
What is Ohm’s law?
It is the flow through a vessel.
Flow = Pressure difference divided by resistance.
Pressure difference is the change in pressure from one point in the vessel to another point. Resistance is the friction as the blood flows along the endothelium of a vessel.
What is laminar flow? Where does it occur?
It is smooth and steady flow, found at the center of a vessel.
What is turbulent flow? Where does it occur?
It is flow that mixes and flows in multiple directions, occurring when:
rate of blood flow is too great for vessel size
sharp turn
rough surface
vessel obstruction/occlusion
What is flow most affected by?
Vessel diameter.
What is pouiselle’s equation for?
F = (pipressure changeradius^4)/(8viscositylength)
AKA more viscous fluids flow slower (like honey/syrup)
Bigger vessels have higher flow
Longer vessels have slower flow
Which BP changes the most during exercise?
SBP. Diastolic decreases barely, but SBP sharply increases and then increases steadily.
What happens if I see a SBP drop during exercise?
Indicative of possible heart failure.
The heart has been stressed to the point where it cannot keep up with the work required by the exercise.
