Nordgren: Heart Pump Flashcards
What are the phases of the cardiac cycle?
- diastole
- Systole:
- Isovolumetric contraction
- Ejection phase
- Isovolumetric relaxation
What is the first step in diastole and what causes it?
- Opening of the AV valves- occurs when LV pressure falls below LA P. Ventricular filling begins.
What is the second step of diastole?
- Open AV
2. Blood from RA empties rapidly into LV
What is the third step of diastole?
- Open AV
- Blood empties from RA
- P in RA/AV rise as champers passively fill as blood returns through veins
What causes the P wave?
Depolarization of the RA causes RA P to rise forcing blood into the ventricle.
When is the P wave important?
KImportant when increased HR because passive fillig time is shortened
What maintains atrial pressure during diastole?
AP is maintained by elastic recoil of the walls of the aorta and other large arteries.
What is the lowest aortic pressure?
Aortic pressure gradually falls during diastole as the aortic blood supplies the vascular bed. The lowest aortic pressure is the DIASTOLIC pressure reached at the end of diastole.
What are the 3 things that proper filling of the ventricles depends on?
- Filling pressure of blood returning to heart and atria
- Ability of AV valves to open fully (not stenotic)
- Ability of ventricular wall to expand passively with little resistance (high compliance)
What is the QRS wave? Why is it important?
AP passes through the AV node to the ventricle. Causing contraction in the LV and intraventricular pressure to rise about that in the RA.
This is the first step of systole!
What closes the AV valve?
Increased pressure
What happens during the isovolumetric contraction phase and when is it?
The chamber is CLOSED and has a FIXED volume as the heart contracts.
(period when mitral valve and AV valve are closed)
When does ventricular ejection begin?
When LV P exceeds that in the aorta cause the AV to open.
What is the pressure difference between the LV and the aorta?
VERY small. The aortic valve orifice is large and presents very little resistance to flow.
What is the peak systolic pressure?
When left ventricular and aortic pressures reach a maximum
What does the T wave represent?
Ventricular relaxation and repolarization
Why does aortic pressure fall during the ejection phase?
Blood is leaving the aorta and large arteries faster than it’s entering from the left ventricle.
What causes the AV valve to close?
LV pressure falls below aortic pressure
What is the incisura in AP?
When a small amt of blood backflow to ventricle as aortic leaflets close> temporary rise in aortic P
What happens to the intraventricular pressure (following the T wave) as ventricular muscles relax?
IV P falls rapidly
What occurs during the isovolumetric relaxation phase?
Relaxation! A period between aortic valve closure and mitral valve opening, that causes the IV pressure to fall below AP.
What is the arterial pulse pressure?
PP= Diastolic - systolic
What is stroke volume?
The amt of blood ejected from the ventricle during a single beat.
SV= EDV-ESV
What is the main difference between the cardiac cycle for the right and left pump?
- Magnitude of the peak systolic pressure is LOWER in the RGIHT because less resistance to flow from lungs vs. systemic organs (sys=24, dia- 8)
What is the jugular venous pulse?
Pressure pulsations in the RA that are transmitted to large veins near the heart
What is the A wave?
atrial contraction
What is the C wave?
bulging of tricuspid valve into the RA d/t ventricular contraction
What is the v wave?
RA and central veins re-filling behind the tricuspid valve (blood returns from peripheral organs)
What is S1?
closure of AV valves
What is S2?
Closure of aortic and pulmonary valves
What is physiological splitting of s2?
When the pulmonic valve closes slightly after the aortic valave inspiration causing an increase in the gap to 30-60 ms.
What S sounds are not normally heard?
S3- presence can indicate LV failure
S4- presence may indicate ventricular diastolic stiffness
What is the ejection fraction equal to?
SV/Peak Volume
What is the underlying basis for ventricular function?
Cardiac muscle length tension behavior
What are the determinants of CO?
CO= HR x SV
How does HR influence CO?
Influences characteristics of diastolic depolarization of pacemaker cells
What do the sympathetic and parasympathetic nerves do to CO?
Immediately effect (w/in 1 bt), cause rapid adjustments to CO
What is preload?
The initial stretching/tension of the cardiomyocytes prior to contraction.
(the end-diastolic pressure/volume that stretches the ventricle to it’s greatest dimensions)
What is preload related to?
The sarcomere length at the end of diastole
What are used as surrogates for the end of preload?
EDV or atrial pressure
What is Starling’s law of the heart?
SV increases as cardiac filling increases
What does an increase in preload do?
- Increases the initial muscle fiber length, thus increasing the extent of shortening during contraction
- Increases the end-diastolic volume and stroke volume
What is afterload?
The pressure that the heart must generate in order to eject blood.
Tension or stress that develops in the cardiomyocytes of the left ventricle during ejection/contraction
What happens to CO as afterload increases?
CO decreases
What is the formula for MAP?
MAP= DP + 1/3PP
What does increased afterload do to cell shortening?
NEGATIVE effect
How does afterload normally effect SV?
Normally it is held CONSTANT and has a MINIMAL effect on SV
What happens to afterload and SV in a pt w/ hypertension or aortic valve obstruction?
Increased afterload
Decreased SV
How does cell shortening relate to contractility?
More shortening= increased contractility
What does the SNS do to contractility?
INCREASES contractility
- upward shift of length tension curve
What does increased contractility do to ESV?
DECREASES it leading to an INCREASE in SV.
What is the ejection fraction?
SV/EDV
What causes an increase in the ejection fraction?
An increase in contractility
What is the primary source of cardiac energy?
ATP form oxidative phosphorylation
What do fetal and newborns use for cardiac energy?
glucose and lactate
What happens to cardiac energetics during severe heart failure?
Observable shift back to glucose metabolism
What is the end product of metabolism by oxidative phosphorylation?
Acetyl CoA
What does Acetyl CoA do?
Enters Krebs cycle in mitochondria and via OXPHOS, ATP is generated
Are anaerobic E sources able to sustain the metabolic demands of the heart?
NO, not for more tha na few mins
What does the heart rely to sustain ATP production?
AEROBIC pathways
Lots of mitochondria
Lots of O binding protein myoglobin
Why is myocardial O2 consumption alpha energy use?
Because it’s almost all from aerobic metabolism
Muscle contraction uses what percent of generated ATP?
75%, 50% which is used for isometric contractoin
What does isometric contraction depend on?
The cardiac afterload
What is stroke work?
Exernal physical work done by LV in 1 beat
What causes an increase in stroke worko?
Increase in preload> SV
Increase in afterload> pressure/work
How do changes in contractility affect O2 requirements?
More O2 needed to contract rapidly than slowly
What is one of the most important determinants of myocardial O2 consumption?
Heart rate
$/min= $/beat x bpm
Waht are strategies to reduce O2 consumption?
Reduce HR (sympathetic drive)
