Integration of Cardiac Function Flashcards
2 mechanisms to control CO
intrinsic - local to heart
- mechanical/muscular (Starling’s law related to contractility)
- electrical/ionic (membrane potential; ionic concentrations)
extrinsic - extra-cardiac neuronal and hormonal signaling pathways
-baroreceptors and chemoreceptors related to sympathetic stimulation and parasympathetic inhibition
neurotransmitter, receptors, second messenger, and functional “results” for sympathetic stimulation of the heart
NE to beta1 (pacemakers and myocetes) that increase cAMP
-cause tachycardia and increased contractility
neurotransmitter, receptors, second messenger, and functional “results” for parasympathetic stimulation of the heart
ACh to M2 (pacemakers, minor myocete effect) that decrease cAMP
-cause bradycardia and decreased contractility
how does CO compare in the aorta and pulmonary artery?
CO is the same in both, b/c they are in series
-it is NOT the sum of flows into aorta and pulmonary arteries
how low does CO go to be defined as hypoxia?
falls below 1/3 normal
what is the relationship between CO, work, and O2 consumption during exercise?
positive linear relationship
how does mild inspiratory hypoxia change CO?
increases CO
-decreased O2 concentration in environment (like at high altitude)
how does chronic anemia change CO?
increases CO
-decreased O2 content in blood when RBC concentration is reduced
how does histotoxic hypoxia change CO?
increases CO
-tissue poisoning involves decreased ability of tissues to utilize O2 as occurs after cyanide ingestion
how does pulmonary disease change CO?
increases CO
-in general, resulting in hypoxemia (lowered O2 concentration in blood)
what are 4 compensatory diseases that increase CO?
- chronic anemia
- histotoxic hypoxia
- pulmonary disease with hypoxemia
- mild inspiratory hypoxia
how does hyperthyroidism change CO?
increases CO b/c increased metabolic rate
how does pregnancy change CO?
increases CO (by 8%) corresponding to increased metabolism
difference between mild anoxia and severe anoxia
mild anoxia: increases CO b/c decrease peripheral resistance
severe anoxia: decreases CO b/c O2 deprivation in heart
how does HTN change CO?
unaltered in most forms
what happens to CO during hemorrhage?
CO is less than 1/2 normal for a significant period of time
-can cause severe shock
what 3 heart diseases decrease CO?
acute myocardial infarction
rheumatic fever
congestive heart failure
effect of body size on CO
CO increases in proportion to size
-CO = k * W^(3/4)
cardiac index and equation
CI = CO/body surface area
-attempt to normalize CO to individuals of different sizes
how does CO change with age?
body metabolism slows with increasing age, as does CO, by about 30% between 20 to 45 years old
-drops from 6 to 5.25 L/min
effect of anxiety on CO
emotional factors increase CO
effect on posture on CO
if laying down to sitting up: CO decreases by 23%
if laying/sitting to standing up, CO increases b/c tensing muscles
effect of temperature on CO
during fever, CO rises due to effects of temperature on metabolic rates of tissue
4 phases of cardiac cycle
- filling phase
- isovolumetric contraction phase
- ejection phase
- isovolumetric relaxation phase
what does the P wave correspond to
atrial depolarization
-while the AV node, bundle of his, bundle branches, and Purkinje network are depolarized as well, they don’t generate voltages large enough to be measured
what does the QRS complex correspond to?
ventricular depolarization (upstrokes)
what does the T-wave correspond to?
ventricular repolarization
what does the ST segment correspond to?
plateau phase (phase 2)
what does the TP segment correspond to?
ventricular diastole
ventricular volume changes in cardiac cycle
- ejection: falls from 120 to 50 mL, corresponding to stroke volume of 70 mL, and EJ of 58%
- filling: occurs during early diastole as mitral and tricuspid valves open
- atrial systole occurs at the end of diastole, with only a small rise in pressure for both right and left hearts, so responsible for only a small increase in ventricular volume
atrial diastole
occurs during ventricular systole
-atrial pressure rises, then falls when mitral valve opens
when does diastole begin?
at the dichrotic notch when aortic valve closes
what happens to ventricular pressure when mitral valve opens?
this is shortly after the beginning of diastole: left ventricular pressure is falling when ventricular volume is increasing
-forward momentum of blood entering ventricles expands them and drops pressure, even though ventricular blood volume is increasing
what happens to dynamic pressure during systole?
ventricular pressure is greater than aortic pressure during rapid ejection phase
- during slow ejection phase, pressure falls so rapidly in LV that LV pressure falls below aortic pressure
- blood continues to flow forward due to forward momentum, but decelerated by reversed pressure gradient
filling phase
- ventricular pressure?
- which valves are open
- how much do ventricles fill?
- how does the ECG count?
ventricles are at low pressure, and tricuspid and mitral valves are open
- ventricles fill from 50 mL to 120 mL blood
- P wave of ECG precedes atrial contraction, and corresponds to atrial depolarization
jugular pulse and it’s A, C, and V waves
follows right atrial pressure
- A = atrial contraction
- C = closure of tricuspid valve
- V = atrial filling and emptying
what do the first and second heart sounds correspond to?
1st: closure of AV valves
2nd: closure of aortic and pulmonic valves
isovolumetric contraction phase
- how does it relate to ECG?
- what happens to ventricular pressure?
- what happens to the valves?
- QRS complex occurs (ventricular depolarization)
- -ventricular muscles contract, so no immediate volume change
- ventricular pressure rapidly increases b/c AV valves rapidly close (first sound)
- pulmonary and aortic valves then open, even though destination pressures initially higher
ejection phase
- what is it the dominant event of?
- how does it correspond to ECG?
once the ventricular pressure exceeds “destination” vasculature
- blood ejected from ventricles in dominant event of systole
- T wave occurs during end half of outflow phase
- at end of outflow phase, ventricular pressure decreases
isovolumetric relaxation phase
- what happens to pressure?
- what sound does it make?
- when does a new cardiac cycle begin?
pressure rapidly drops in both ventricles (little blood flow in or out)
- pulmonic and aortic valves close (beginning of diastole)
- when ventricular pressure drops below atria, mitral and tricuspid valves open, and new cardiac cycle begins
how do increased contractility and pre-load effect stroke volume?
both increase SV
- increased contractility = decreased ESV
- increased pre-load = increased EDV
when and how would you want to increase contractility?
treat CHF or infarction via positive inotropic drugs
what can increased preload be an adaptive response to?
aortic stenosis, ventricular hypertrophy, anemias, hyperthyroidism
what does increased afterload do to SV?
increased afterload will decrease stroke volume b/c needs more pressure than normal to eject blood
-can be due to aortic valve defects or HTN
how does atrial filling pressure, ventricular filling time, and HR effect SV?
AFP: increasing will impede venous return, thus decreasing EDV to decrease SV
VFT: increased time causes increased EDV, so increased SV
HR: increased will decrease diastole time, which decreases EDV to decrease SV
how is rhythmicity provided?
provided by intrinsic mechanisms of SA node
which chambers of heart contract first, second, third, and fourth
- RA
- LA (both only contribute a little)
- LV (like squeezing toothpaste tube)
- RV (like a bellows, and both eject about same volume)
how do mitral/tricuspid valves open/close in succession?
mitral valve closes before tricuspid, but tricuspid opens before mitral
-this is because LV contraction is before RV contraction, but drop in pressure in LV is larger and takes longer than in right ventricle
how do aortic and pulmonary valves open/close in succession?
pulmonary valve opens before aortic valve, but aortic closes before pulmonary valve
-this is because pulmonary artery pressure is less than aortic pressure
what are the 4 heart sounds?
- closure of AV valves (lub)
- closure of aortic and pulmonary valves (dub)
- particularly evident in kids; diastolic filling “gallop” from recoil of ventricles that have limited distensibility/compliance
- atrial contraction “gallop” that is usually pathologic
